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Contents Wiring diagrams Section: Communication Devices All sections

Data Communication System Cadillac ATS I

Communication Devices 15 illustrations ~33531 words

Scheme 3

Scheme 3: Low Speed GMLAN
Scheme 3: Low Speed GMLAN

Scheme 4

Scheme 4: High Speed GMLAN (1 of 2)
Scheme 4: High Speed GMLAN (1 of 2)

Scheme 5

Scheme 5: High Speed GMLAN (2 of 2)
Scheme 5: High Speed GMLAN (2 of 2)

Scheme 6

Scheme 6: Chassis High Speed GMLAN
Scheme 6: Chassis High Speed GMLAN

Scheme 7

Scheme 7: MOST Bus and Communications Enable
Scheme 7: MOST Bus and Communications Enable

Scheme 8

Scheme 8: Object High Speed GMLAN (UGN or UVZ)
Scheme 8: Object High Speed GMLAN (UGN or UVZ)

Scheme 9

Scheme 9: Communications Enable - High Speed GMLAN
Scheme 9: Communications Enable - High Speed GMLAN

Scheme 10

Scheme 10: Communications Enable - Object High Speed GMLAN
Scheme 10: Communications Enable - Object High Speed GMLAN

Scheme 11

Scheme 11: Linear Interconnect Network (LIN) Bus 1, 2, 3 and 11
Scheme 11: Linear Interconnect Network (LIN) Bus 1, 2, 3 and 11

Scheme 12

Scheme 12: Linear Interconnect Network (LIN) Bus 8, 9, 10 and 12
Scheme 12: Linear Interconnect Network (LIN) Bus 8, 9, 10 and 12

Scheme 13

Scheme 13: Module Power and Ground
Scheme 13: Module Power and Ground

Scheme 14

Scheme 14: System Reference (1 of 3)
Scheme 14: System Reference (1 of 3)

Scheme 15

Scheme 15: System Reference (2 of 3)
Scheme 15: System Reference (2 of 3)

Scheme 16

Scheme 16: System Reference (3 of 3)
Scheme 16: System Reference (3 of 3)

Diagnostic Code Index

DTCDescription
DTC B1000DTC B1000 Electronic Control Unit
DTC B1001DTC B1001 Option Configuration
DTC B101DDTC B101D Electronic Control Unit Hardware
DTC B101EDTC B101E Electronic Control Unit Software
DTC C056DDTC C056D Electronic Control Unit Hardware
DTC C056EDTC C056E Electronic Control Unit Software
DTC P0601-P0606, P060A, P062F, or P262BDTC P0601 Control Module Read Only Memory Performance DTC P0602 Control Module Not Programmed DTC P0603 Control Module Long Term Memory Reset DTC P0604 Control Module Random Access Memory Performance DTC P0605 Control Module Programming Read Only Memory Performance DTC P0606 Control Module Processor Performance DTC P060A Control Module Monitoring Processor Performance DTC P062F Control Module Long Term Memory Performance DTC P262B Control Module Power Off Timer Performance
DTC U0001DTC U0001 00 High Speed CAN Communication Bus Malfunction
DTC U0020DTC U0020 Low Speed CAN Bus
DTC U0028DTC U0028 MOST Bus
DTC U0029DTC U0029 MOST Bus Performance
DTC U0073 or U2100DTC U0073 Control Module Communication Bus A Off DTC U2100 CAN Bus Communication
DTC U0074DTC U0074 Control Module Communication Bus B Off
DTC U0075DTC U0075 00 Control Module Communication Object Detection CAN Bus Off
DTC U0077DTC U0077 00 Control Module Communication Chassis Expansion CAN Bus Off
DTC U0078DTC U0078 Control Module Communication Low Speed CAN Bus Off
DTC U0100-U02FFModule Error. See Control Module U Code List
DTC U0300-U0336Module Error. See Control Module U Code List
DTC U0400-U05FFModule Error. See Control Module U Code List
DTC U1500-U15FFModule Error. See Control Module U Code List
DTC U1814DTC U1814 Powertrain Wake-Up Communication Circuit
DTC U1833DTC U1833 Lost Communication with Electronic Brake Control Module on Chassis Expansion CAN Bus
DTC U184ADTC U184A Lost Communication with Body Control Module on Low Speed CAN Bus
DTC U18B9-U18BFDTC U18B9 Primary High Speed CAN Bus Subnet Configuration List DTC U18BF Secondary High Speed CAN Bus Subnet Configuration List
DTC U2098DTC U2098 00 MOST Communication Enable Circuit Malfunction DTC U2098 02 MOST Communication Enable Circuit Short to Ground
DTC U2099DTC U2099 High Speed Communication Enable Circuit
DTC U209EDTC U209E Object Detection Control Module High Speed Communication Enable Circuit 1
DTC U209FDTC U209F Object Detection Control Module High Speed Communication Enable Circuit 2
DTC U2101DTC U2101 CAN Bus Maximum List of Control Modules

DIAGNOSTIC CODE INDEX

Control Module U Code List

This list includes all Data Communications related U-code DTCs in alphanumeric order with descriptors for all devices. Not all DTCs listed will be applicable to all vehicles.

For symptom byte information, refer to Symptom Byte List .

DTCDTC Descriptor
U0001High Speed CAN Bus Malfunction
U0002High Speed CAN Bus
U0009High Speed CAN Bus [-] Shorted to Bus [+]
U0020Low Speed CAN Bus
U0028MOST Bus
U0029MOST Bus Performance
U0073Control Module Communication Bus A Off
U0074Control Module Communication Bus B Off
U0075Control Module Communication Object Detection CAN Bus Off
U0077Control Module Communication Chassis Expansion CAN Bus Off
U0078Control Module Communication Low Speed CAN Bus Off
U007AControl Module Communication High Voltage Energy Management CAN Bus Off
U0100Lost Communication With Engine Control Module
U0101Lost Communication With Transmission Control Module
U0102Lost Communication with Transfer Case Control Module
U0103Lost Communication with Shift Lever Module
U0104Lost Communication With Cruise Control Module
U0105Lost Communication with Fuel Injector Control Module
U0106Lost Communication with Glow Plug Control Module
U0109Lost Communication with Fuel Pump Control Module (2013 and prior)
Lost Communication with Chassis Control Module (2014 and beyond)
U010ELost Communication with Reductant Sensor Module
U010FLost Communication with Air Conditioning Control Module
U0111Lost Communication with Battery Energy Control Module
U0112Lost Communication with Battery Energy Control Module
U0115Lost Communication with Engine Control Module B
U0117Lost Communication With Power Take-Off Control Module
U0121Lost Communication With Electronic Brake Control Module
U0122Lost Communication With Vehicle Stability Control Module
U0123Lost Communication with Yaw Rate Sensor Module
U0125Lost Communication With Multi-axis Acceleration Sensor Module
U0126Lost Communication With Steering Wheel Angle Sensor Module
U0128Lost Communication With Park Brake Control Module
U0129Lost Communication with Brake System Control Module
U012ALost Communication With Chassis Control Module
U0130Lost Communication With Electric Power Steering Control Module
U0131Lost Communication With Power Steering Control Module
U0132Lost Communication With Suspension Control Module
U0133Lost Communication With Air Suspension Control Module
U0136Lost Communication With Differential Control Module - Rear
U0137Lost Communication with Trailer Brake Control Module
U0139Lost Communication With Suspension Control Module
U0140Lost Communication With Body Control Module
U0146Lost Communication with Infotainment Gateway Module
U0151Lost Communication With Inflatable Restraint Sensing and Diagnostic Module
U0155Lost Communication With Instrument Cluster
U0158Lost Communication With Head-Up Display
U0159Lost Communication With Parking Assist Control Module
U0160Lost Communication With Chime Alarm Control Module
U0164Lost Communication with HVAC Control Module
U0166Lost Communication with Auxiliary Heater Control Module
U0167Lost Communication with Immobilizer Control Module
U0168Lost Communication With Keyless Entry Control Module
U016BLost Communication with Electric A/C Compressor Control Module
U0170Lost Communication with Passenger Presence Detection Sensor Module
U0181Lost Communication With Headlamp Leveling Control Module
U0182Lost Communication With Lighting Control Module - Front
U0184Lost Communication With Radio
U0186Lost Communication With Speaker Amplifier Module
U0196Lost Communication With Rear Audio Control Module
U0191Lost Communication With Television
U0193Lost Communication With Digital Radio Receiver Control Module
U0197Lost Communication With Telephone Control Module
U0198Lost Communication With Telematic Control Module
U0201Lost Communication With Transfer Case Control Module
U0203Lost Communication With Left Rear Door Switch Panel Control Module
U0204Lost Communication With Right Rear Door Switch Panel Control Module
U0207Lost Communication With Moveable Roof Control Module
U0208Lost Communication with Seat Memory Control Module
U0209Lost Communication With Front Seat Heating Control Module
U0210Lost Communication With Rear Seat Heating Control Module
U0230Lost Communication With Liftgate Control Module
U0232Lost Communication with Side Object Detection Control Module - Left
U0233Lost Communication with Side Object Detection Control Module - Right
U0236Lost Communication With Steering Column Lock Module
U0237Lost Communication With Multimedia Player Interface Module
U023ALost Communication With Vehicle Direction Camera Control Module (without UGN)
Lost Communication With Active Safety Control Module (with UGN)
U0248Lost Communication with Remote Accessory Module
U0249Lost Communication with Entertainment Control Module - Rear
U0250Lost Communication with Impact Classification System Module
U0252Lost Communication With Trailer Interface Control Module
U0254Lost Communication With Remote Start Module
U0255Lost Communication With Info Display Module
U0256Lost Communication With Infotainment Faceplate Control Module
U0257Lost Communication With Info Display Module/Infotainment Faceplate Control Module
U025BLost Communication with Special Purpose Vehicle Control Module "C"
U0264Lost Communication With Camera Module - Rear
U0265Lost Communication with Left Front Short Range Radar Sensor Module
U0268Lost Communication with Right Front Short Range Radar Sensor Module
U0269Lost Communication with Front Long Range Object Sensor
U026ALost Communication with Frontview Camera Module
U026BLost Communication with Rear Short Range Object Sensor
U0293Lost Communication with Hybrid/EV Powertrain Control Module
U029DLost Communication with NOx Sensor 1 Module
U029ELost Communication with NOx Sensor 2 Module
U02A3Lost Communication With Particulate Matter Sensor Module
U0301Software Incompatibility with Engine Control Module
U0302Software Incompatibility with Transmission Control Module
U0305Software Incompatibility With Cruise Control Module
U0315Software Incompatibility with Electronic Brake Control Module
U0401Invalid Data Received From Engine Control Module
U0402Invalid Data Received From Transmission Control Module
U0403Invalid Data Received From Transfer Case Control Module
U0405Invalid Data Received From Cruise Control Module
U0415Invalid Data Received From Electronic Brake Control Module
U0416Invalid Data Received From Vehicle Dynamics Control Module
U0417Invalid Data Received From Park Brake Control Module
U0418Invalid Data Received From Brake System Control Module
U0420Invalid Data Received From Power Steering Control Module
U0421Invalid Data Received From Suspension Control Module
U0422Invalid Data Received From Body Control Module
U0423Invalid Data Received From Instrument Cluster
U0424Invalid Data Received From HVAC Control Module
U0428Invalid Data Received From Steering Wheel Angle Sensor Module
U042BInvalid Data Received From Chassis Control Module
U0431Invalid Data Received From Body Control Module "A"
U0432Invalid Data Received From Multi-axis Acceleration Sensor Module
U0437Invalid Data Received From Differential Control Module - Rear
U0438Invalid Data Received From Trailer Brake Control Module
U0452Invalid Data Received From Inflatable Restraint Sensing and Diagnostic Module
U045AInvalid Data Received From Parking Assist Control Module "A"
U0465Invalid Data Received From Power Take-Off Control Module
U0499Invalid Data Received From Telematic Control Module
U0513Invalid Data Received From Yaw Rate Sensor Module
U053BInvalid Data Received From Active Safety Control Module
U056BInvalid Data Received From Camera Module - Front
U0594Invalid Data Received From Hybrid/EV Powertrain Control Module
U1501LIN Bus
U1502LIN Bus
U1505LIN Bus
U1509LIN Bus
A26 HVAC Controls / P17 Info Display Module Lost Communication with K33 HVAC Control Module on LIN Bus
U150ELIN Bus
A22 Radio Controls / P17 Info Display Module Lost Communication with A11 Radio on LIN Bus
U150FLIN Bus
A22 Radio Controls / P17 Info Display Module Lost Communication with K74 Human Machine Interface Control Module on LIN Bus
U1510K9 Body Control Module Lost Communication with B67 Ultrasonic Intrusion Sensor / B165 Content Theft Deterrent Sensor Module on LIN Bus
K33 HVAC Control Module Lost Communication with A26 HVAC Controls / A20 Radio/HVAC Controls / P17 Info Display Module on LIN Bus
A11 Radio Lost Communication with A20 Radio/HVAC Control / P17 Info Display Module on LIN Bus
K39 Liftgate Control Module Lost Communication with K171 Hands-Free Liftgate Sensor Control Module / S45A Liftgate Control Switch - Exterior on LIN Bus
P16 Instrument Cluster Lost Communication with S70R Steering Wheel Controls Switch - Right on LIN Bus
U1511K26 Headlamp Control Module / K28 Headlamp Leveling Control Module Lost Communication with E13L Headlamp - Left on LIN Bus
K40 Seat Memory Control Module Lost Communication with K99 Steering Column Position Control Module on LIN Bus
U1512K26 Headlamp Control Module / K28 Headlamp Leveling Control Module Lost Communication with E13R Headlamp - Right on LIN Bus
U1513K26 Headlamp Control Module / K28 Headlamp Leveling Control Module Lost Communication with E13L Headlamp - Left on LIN Bus
U1514K26 Headlamp Control Module / K28 Headlamp Leveling Control Module Lost Communication with E13R Headlamp - Right on LIN Bus
U1515K9 Body Control Module Lost Communication with M75 Windshield Wiper Motor / M75L Windshield Wiper Motor Module - Left on LIN Bus
U1516K9 Body Control Module Lost Communication with B110 Battery Sensor Module on LIN Bus
U1517K9 Body Control Module Lost Communication with K62 Sunroof Sunshade Motor Module on LIN Bus
U1518P16 Instrument Cluster Lost Communication with K78 Head-Up Display Module / P29 Head-Up Display on LIN Bus
U1519K40 Seat Memory Control Module Lost Communication with S52 Outside Rearview Mirror Switch on LIN Bus
K40 Seat Memory Control Module Lost Communication with K96 Mirror Control Module / K96D Mirror Control Module - Driver / K96L Mirror Control Module - Left on LIN Bus
U151AK9 Body Control Module Lost Communication with B117 Rain Sensor / B177 Rain/Ambient Light Sensor Module / B200 Rain Sensor Module on LIN Bus
U151BK9 Body Control Module Lost Communication with K61 Sunroof Control Module on LIN Bus
K40 Seat Memory Control Module Lost Communication with S79P Window Switch - Passenger on LIN Bus
U151CK33 HVAC Control Module Lost Communication with K33A HVAC Control Module - Auxiliary on LIN Bus
U1520K9 Body Control Module Lost Communication with P4 Security Siren / P25 Power Sounder Content Theft Deterrent Alarm Module on LIN Bus
U1521K9 Body Control Module Lost Communication with S48E Multifunction Switch - Center Console on LIN Bus
K26 Headlamp Control Module / K28 Headlamp Leveling Control Module Lost Communication with E13L Headlamp - Left on LIN Bus
U1522K9 Body Control Module Lost Communication with K65 Tire Pressure Indicator Module / B178 Tire Pressure Sensor Locator Module on LIN Bus
K26 Headlamp Control Module / K28 Headlamp Leveling Control Module Lost Communication with E13R Headlamp - Right on LIN Bus
U1523K26 Headlamp Control Module / K28 Headlamp Leveling Control Module Lost Communication with E13L Headlamp - Left on LIN Bus
U1524K9 Body Control Module Lost Communication with K29 Seat Heating Control Module / K29F Seat Heating Control Module - Front on LIN Bus
K26 Headlamp Control Module / K28 Headlamp Leveling Control Module Lost Communication with E13R Headlamp - Right on LIN Bus
U1526K9 Body Control Module Lost Communication with K29R Seat Heating Control Module - Rear on LIN Bus
U1528K40D Seat Memory Control Module - Driver Lost Communication with S64D Seat Adjuster Switch - Driver on LIN Bus
K40P Seat Memory Control Module - Passenger Lost Communication with S64P Seat Adjuster Switch - Passenger on LIN Bus
U152CK9 Body Control Module Lost Communication with K18 Compass Module on LIN Bus
U152DK9 Body Control Module Lost Communication with P2 Transmission Shift Lever Position Indicator on LIN Bus
U1530K9 Body Control Module Lost Communication with M35P Window Motor Module - Passenger / M74P Window Motor - Passenger on LIN Bus
U1531K26 Headlamp Control Module / K28 Headlamp Leveling Control Module Lost Communication with E13LA Headlamp Assembly - Left on LIN Bus
U1532K26 Headlamp Control Module / K28 Headlamp Leveling Control Module Lost Communication with E13RA Headlamp Assembly - Right on LIN Bus
U1534K9 Body Control Module Lost Communication with M74D Window Motor - Driver on LIN Bus
U1538K9 Body Control Module Lost Communication with S79D Window Switch - Driver on LIN Bus
U153AK9 Body Control Module Lost Communication with S79P Window Switch - Passenger on LIN Bus
U1540K9 Body Control Module Lost Communication with M74RR Window Motor - Right Rear on LIN Bus
U1544K9 Body Control Module Lost Communication with M74LR Window Motor - Left Rear on LIN Bus
U1548K9 Body Control Module Lost Communication with S79LR Window Switch - Left Rear on LIN Bus
U1549K9 Body Control Module Lost Communication with M45 Rear Wiper Motor on LIN Bus
U154AK9 Body Control Module Lost Communication with S79RR Window Switch - Right Rear on LIN Bus
U154BK9 Body Control Module Lost Communication with K49 Rear Seat Control Module on LIN Bus
U1550K9 Body Control Module Lost Communication with S31D Seat Heating and Cooling Switch - Driver on LIN Bus
U1556K38 Chassis Control Module Lost Communication with K133 Trailer Brake Power Control Module on LIN Bus
U1558K9 Body Control Module Lost Communication with S31P Seat Heating and Cooling Switch - Passenger on LIN Bus
U15E1A11 Radio Lost Communication with A26 HVAC Controls / P17 Info Display Module on LIN Bus
U15F0K74 Human Interface Control Module Lost Communication with P17 Info Display Module on LIN Bus
U179314V Power Module Lost Communication with Hybrid/EV Powertrain Control Module on Powertrain Expansion Communication Bus
U179514V Power Module Powertrain Expansion Communication Bus Off
U179ALost Communication with Hybrid/EV Powertrain Control Module 2
U1803Lost Communication with Hybrid/EV Powertrain Control Module 2
U1804Lost Communication with Inside Rearview Mirror Control Module
U1806Battery Energy Control Module High Voltage Energy Management CAN Bus Off
U1807Battery Charger Control Module High Voltage Energy Management CAN Bus Off
U180AElectric A/C Compressor Control Module High Speed CAN Bus Off
U180BBattery Energy Control Module High Speed CAN Bus Off
U180CBattery Charger Control Module High Speed CAN Bus Off
U180DElectronic Brake Control Module Chassis Expansion CAN Bus Off
U1811Battery Energy Control Module Powertrain Expansion CAN Bus Off
U1814Powertrain Wake-Up Communication Circuit
U1815Lost Communication with Drive Motor Control Module 1 on Bus B
U1816Lost Communication with Drive Motor Control Module B on Bus B
U1817Lost Communication with Hybrid/EV Powertrain Control Module on Powertrain Expansion CAN Bus
U1818Lost Communication with Engine Control Module on Powertrain Expansion Communication Bus
U1821Lost Communication with 14V Power Module on Powertrain Expansion Communication Bus
U1826Lost Communication with Multi-Axis Acceleration Sensor Module on Powertrain Expansion CAN Bus
U1827Lost Communication with Steering Angle Sensor Module on Powertrain Expansion CAN Bus
U182AHybrid/EV Powertrain Control Module Lost Communication with Battery Energy Control Module on Powertrain Expansion CAN Bus
U182DLost Communication with Hybrid/EV Powertrain Control Module 2 on Powertrain Expansion Communication Bus
U182EDrive Motor Control Module 1 Lost Communication with Hybrid/EV Powertrain Control Module 2 on Powertrain Expansion Communication Bus
U182FDrive Motor Control Module 2 Lost Communication with Hybrid/EV Powertrain Control Module 2 on Powertrain Expansion Communication Bus
U1831Drive Motor Control Module 1 Lost Communication with Hybrid/EV Powertrain Control Module on Powertrain Expansion CAN Bus
U1833Lost Communication with Electronic Brake Control Module on Chassis Expansion CAN Bus
U1838Lost Communication with Battery Charger Control Module on High Voltage Energy Management CAN Bus
U1839Auxiliary Transmission Fluid Pump Control Module Lost Communication with Engine Control Module
U183ALost Communication with Telematics Communication Interface Control Module on High Speed CAN Bus
U183BAuxiliary Transmission Fluid Pump Control Module Lost Communication with Transmission Control Module
U183CAuxiliary Transmission Fluid Pump Control Module Lost Communication with Hybrid/EV Powertrain Control Module 2 on Powertrain Expansion Communication Bus
U183ELost Communication with Telematics Communication Interface Control Module on Low Speed CAN Bus
U1844Battery Energy Control Module Lost Communication with Hybrid/EV Powertrain Control Module on Bus B
U1845Drive Motor Control Module 1 Lost Communication with Hybrid/EV Powertrain Control Module
U1846Drive Motor Control Module 2 Lost Communication with Hybrid/EV Powertrain Control Module
U1847Drive Motor Control Module 1 Lost Communication with Battery Energy Control Module on Powertrain Expansion CAN Bus
U1849Drive Motor Control Module 1 Lost Communication with Transmission Control Module
U184ALost Communication with Body Control Module on Low Speed CAN Bus
U184BLost Communication with Remote Heater and Air Conditioning Control Module on Low Speed CAN Bus
U184CLost Communication with Instrument Cluster on Low Speed CAN Bus
U184DLost Communication with Radio on Low Speed CAN Bus
U184ELost Communication with Inflatable Restraint Sensing and Diagnostic Module on Low Speed CAN Bus
U184FElectric A/C Compressor Control Module Lost Communication with Engine Control Module
U1850Drive Motor Control Module 2 Lost Communication with Transmission Control Module
U1858Electronic Brake Control Module Lost Communication with Hybrid/EV Powertrain Control Module on Chassis Expansion CAN Bus
U185ALost Communication with Battery Energy Control Module on High Voltage Energy Management CAN Bus
U185BBattery Energy Control Module Lost Communication with Hybrid/EV Powertrain Control Module 2 on High Voltage Energy Management CAN Bus
U185CBattery Charger Control Module Lost Communication with Hybrid/EV Powertrain Control Module 2 on High Voltage Energy Management CAN Bus
U185DFuel Injector Control Module Lost Communication with Engine Control Module
U185EFuel Injector Control Module Lost Communication with Body Control Module
U1860Electric A/C Compressor Control Module Lost Communication with Hybrid/EV Powertrain Control Module 2
U1861Battery Charger Control Module Lost Communication with Engine Control Module
U186AElectronic Brake Control Module Lost Communication with Engine Control Module
U186BElectronic Brake Control Module Lost Communication with Transmission Control Module
U1875Drive Motor Control Module 1 Lost Communication with Battery Energy Control Module
U1876Drive Motor Control Module 1 Lost Communication with Engine Control Module
U1879Drive Motor Control Module 2 Lost Communication with Engine Control Module
U1885Battery Energy Control Module Lost Communication with Hybrid/EV Powertrain Control Module
U1886Battery Energy Control Module Lost Communication with Engine Control Module
U1888Hybrid/EV Powertrain Control Module Lost Communication with Battery Energy Control Module
U18A1Lost Communication with Coolant Temperature Control Module on High Voltage Energy Management CAN Bus
U18A2Lost Communication with Fuel Pump Driver Control Module
U18A3Lost Communication with Human Machine Interface Control Module
U18A4Lost Communication with Hybrid/EV Battery DC Charging Communications Gateway Module on High Voltage Energy Management CAN Bus
U18A5Lost Communication with Fuel Injector Control Module on Powertrain Expansion CAN Bus
U18A6Lost Communication with Right Object Detection Control Module on Dedicated Bus 1
U18B9Primary High Speed CAN Bus Subnet Configuration List
U18BFSecondary High Speed CAN Bus Subnet Configuration List
U1900Lost Communication With Speech to Text Interface Module
U1901Lost Communication with Infotainment Multifunction Switch Module
U2098MOST Communication Enable Circuit
U2099High Speed Communication Enable Circuit
U209EObject Detection Control Module High Speed Communication Enable Circuit 1
U209FObject Detection Control Module High Speed Communication Enable Circuit 2
U2100CAN Bus Communication
U2101CAN Bus Maximum List of Control Modules
U2103Fewer Controllers On Bus Than Programmed
U2105Lost Communication with Engine Control Module
U2106Lost Communication with Transmission Control Module
U2107Lost Communication with Body Control Module
U2108Lost Communication with Electronic Brake Control Module
U2125Lost Communication with Telematic Unit
U2127Lost Communication with Front HVAC Control Module
U2139Lost Communication with Column Integration Module
U2144Lost Communication with Distance Sensing Cruise Control Module
U216ALost Communication with Front Object Detection Control Module
U216BLost Communication with Rear Object Detection Control Module
U2176Lost Communication with Power Take-Off Control Module
U2178Lost Communication With Trailer Interface Control Module
U2400Fuel Injector Control Module High Speed CAN Bus Off
U2401Battery Energy Control Module Dedicated Bus 1 Off
U2501Invalid Data Received From Hybrid/EV Powertrain Control Module 2
U2502Invalid Data Received From Electronic Brake Control Module on Chassis Expansion CAN Bus
U2503Invalid Data Received From Object Detection Control Module
U2504Invalid Data Received From Trailer Brake Driver Control Module
U2505Invalid Data Received from Human Machine Interface Control Module on MOST Bus
U2506Invalid Data Received From Dual Battery Control Module
U2507Invalid Data Received from Instrument Cluster on MOST Bus
U2508Invalid Data Received from Audio Amplifier on MOST Bus
U2602Battery Energy Control Module Lost Communication with Hybrid/EV Powertrain Control Module 2
U2603Battery Energy Control Module Lost Communication with Hybrid/EV Battery Interface Control Module 1
U2604Battery Energy Control Module Lost Communication with Hybrid/EV Battery Interface Control Module 2
U2605Battery Energy Control Module Lost Communication with Hybrid/EV Battery Interface Control Module 3
U2606Battery Energy Control Module Lost Communication with Hybrid/EV Battery Interface Control Module 4
U2608Electric A/C Compressor Control Module Lost Communication with Hybrid/EV Powertrain Control Module
U2609Battery Charger Control Module Lost Communication with Hybrid/EV Powertrain Control Module
U2611Auxiliary Transmission Fluid Pump Control Module Lost Communication with Hybrid/EV Powertrain Control Module
U2612Battery Charger Control Module Lost Communication with Hybrid/EV Powertrain Control Module 2
U2613Drive Motor 1 Control Module Lost Communication with Hybrid/EV Powertrain Control Module 2
U2614Drive Motor 2 Control Module Lost Communication with Hybrid/EV Powertrain Control Module 2
U2615Auxiliary Transmission Fluid Pump Control Module Lost Communication with Hybrid/EV Powertrain Control Module 2
U2616Fuel Pump Driver Control Module Lost Communication with ECM
U2617Battery Energy Control Module Lost Communication with Hybrid/EV Battery Interface Control Module 5
U2618Battery Energy Control Module Lost Communication with Hybrid/EV Battery Interface Control Module 6
U2619Battery Energy Control Module Lost Communication with Hybrid/EV Battery Interface Control Module 7
U2620Battery Energy Control Module Lost Communication with Hybrid/EV Battery Interface Control Module 8
U2621Battery Energy Control Module Lost Communication with Hybrid/EV Battery Interface Control Module 9
U2622Battery Energy Control Module Lost Communication with Hybrid/EV Battery Interface Control Module 10

Control Module U Code List

Diagnostic Instructions

  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

DTC Descriptor

For symptom byte information, refer to Symptom Byte List .

Circuit/System Description

The internal fault detection is handled inside the device. The symptom byte information is for engineering reference only. No external circuit diagnosis is involved.

Conditions for Running the DTC

The device runs the program to detect an internal fault when power up is commanded. The only requirements are voltage and ground. This program runs even if the voltage is out of the valid operating range.

Conditions for Setting the DTC

The device has detected an internal malfunction.

Action Taken When the DTC Sets

The device refuses all additional inputs.

Conditions for Clearing the DTC

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

  1. This DTC may be stored as a history DTC without affecting the operation of the device.
  2. If stored only as a history DTC and not retrieved as a current DTC, do not replace the device.
  3. If this DTC is retrieved as both a current and history DTC, replace the device that set the DTC.

Reference Information

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

  1. Ignition ON.
  2. Verify DTC B1000 is not set. If DTC B1000 is set Replace the device that set the DTC. If DTC B1000 is not set
  3. All OK

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup

  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

Some devices must be configured with serial numbers, vehicle options, or other information. If a device was not properly configured after installation that device may set DTC B1001. The symptom byte information is for engineering reference only. No external circuit diagnosis is involved.

Battery voltage is between 9-16 V and data link communications operate normally.

The device is not configured properly.

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify DTC B1001 is not set. If DTC B1001 is set Program the device that set the DTC. Verify the DTC does not set. If the DTC sets, replace the device that set the DTC. If the DTC does not set All OK. If DTC B1001 is not set
  3. All OK

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup

  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

The internal fault detection is handled inside the device. The symptom byte information is for engineering reference only. No external circuit diagnosis is involved.

  1. The device runs the program to detect an internal fault when power up is commanded. The only requirements are voltage and ground. This program runs even if the voltage is out of the valid operating range.
  2. The keyless entry control module will set this DTC with symptom byte 39 when the keyless entry control module antenna is activated.

The device has detected an internal malfunction.

The device refuses all additional inputs.

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.
  1. This DTC may be stored as a history DTC without affecting the operation of the device.
  2. Do not replace a device based only on DTC B101D being set in history with the exception of the following devices: K36 Inflatable Restraint Sensing and Diagnostic Module (SDM) K85 Passenger Presence Module
  3. If DTC B101D is set as current, replace the appropriate device.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify DTC B101D is not set. If DTC B101D is set Replace the device that set the DTC. If DTC B101D is not set
  3. All OK

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup

  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

Some devices must be configured with specific software, serial numbers, vehicle options, or other information. If a device was not properly configured after installation that module may set DTC B101E. The symptom byte information is for engineering reference only. No external circuit diagnosis is involved.

Battery voltage is between 9-16 V and data link communications operate normally.

The device is not configured properly.

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify that DTC U0028 or U0029 is not set. If any of the DTCs are set Refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) . If none of the DTCs are set
  3. Verify DTC B101E is not set. If DTC B101E is set Program the device that set the DTC. Verify the DTC does not set. If the DTC sets, replace the device that set the DTC. If the DTC does not set All OK. If DTC B101E is not set
  4. All OK

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup

  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

The internal fault detection is handled inside the device. The symptom byte information is for engineering reference only. No external circuit diagnosis is involved.

The device runs the program to detect an internal fault when power up is commanded. The only requirements are voltage and ground. This program runs even if the voltage is out of the valid operating range.

The device has detected an internal malfunction.

The device refuses all additional inputs.

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.
  1. This DTC may be stored as a history DTC without affecting the operation of the device.
  2. If stored only as a history DTC and not retrieved as a current DTC, do not replace the device.
  3. If this DTC is retrieved as both a current and history DTC, replace the device that set the DTC.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify DTC C056D is not set. If DTC C056D is set in a device that can be programmed Program the device that set the DTC. Verify the DTC does not set. If the DTC sets, replace the device that set the DTC. If the DTC does not set All OK. If DTC C056D is set in a device that cannot be programmed Replace the device that set the DTC. If DTC C056D is not set
  3. All OK

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup

  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

Some devices must be configured with specific software, serial numbers, vehicle options, or other information. If a device was not properly configured after installation that module may set DTC C056E. The symptom byte information is for engineering reference only. No external circuit diagnosis is involved.

Battery voltage is between 9-16 V and data link communications operate normally.

The device is not configured properly.

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool References

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify DTC C056E is not set. If DTC C056E is set Program the device that set the DTC. Verify the DTC does not set. If the DTC sets, replace the device that set the DTC. If the DTC does not set All OK. If DTC C056E is not set
  3. All OK

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup

  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

This diagnostic applies to internal microprocessor integrity conditions within the device. This diagnostic also addresses if the device is not programmed. The device monitors its ability to read and write to the memory. It also monitors a timing function. No external circuits are involved.

  1. The ignition is ON.
  2. The system voltage is greater than 9.5 V.

The device detects an internal malfunction or incomplete programming.

DTCs P0601-P0606, P060A, P062F, and P262B are Type A DTCs.

DTCs P0601-P0606, P060A, P062F, and P262B are Type A DTCs.

If stored only as a history DTC and not retrieved as a current DTC, do not replace the device.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

DTC Type Reference

Scan Tool References

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify that DTC P0602 is not set. If DTC P0602 is set Program the device that set the DTC. Verify that the DTC does not set. If the DTC sets, replace the device that set the DTC. If the DTC does not set All OK. If DTC P0602 is not set
  3. Verify that DTC P0601, P0603, P0604, P0605, P0606, P060A, P062F, or P262B is not set. If any of the DTCs are set Replace the device that set the DTC. If none of the DTCs are set
  4. All OK

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup

  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Circuit Description

Devices connected to the GMLAN serial data circuits monitor for serial data communications on the GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the devices. Each device on GMLAN network maintains a transmit error counter and a receive error counter. The counter values increase with detected errors and will decrease with error-free messages. If the transmit error counter value exceeds 255 the device removes itself from the network and a DTC U0001 will be set.

  1. System voltage is in the normal operating voltage range.
  2. The vehicle power mode requires serial data communication to occur.

A certain number of no valid transmitted messages on the GMLAN serial data circuits are detected by the device.

  1. The device suspends all message transmission.
  2. The device uses default values for all parameters received on the GMLAN serial data circuits.
  3. The device inhibits the setting of all other GMLAN communication DTCs.
  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

This DTC may not be retrieved with a current status. Diagnosis is accomplished via the symptom, Scan Tool Does Not Communicate with High Speed GMLAN Device. Refer to Scan Tool Does Not Communicate with High Speed GMLAN Device in order to isolate an intermittent condition caused by a short on the GMLAN serial data circuits.

  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

DTC Descriptors

For symptom byte information, refer to Symptom Byte List .

Devices connected to the GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have programmed information about what messages are needed to be exchanged on the serial data circuits. The messages are also supervised and some periodic messages are used by the receiver device as an availability indication of the transmitter device.

Conditions for Running the DTCs

  1. Supply voltage to the devices is in the normal operating range.
  2. The vehicle power mode requires serial data communication to occur.
  3. The DTC U2100 does not have a current status.

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTCs Sets

The device uses a default value for the missing parameter.

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Diagnosis of this DTC is accomplished via the symptom or an additional DTC. Refer to Scan Tool Does Not Communicate with Low Speed GMLAN Device , or Diagnostic Trouble Code (DTC) List - Vehicle .

  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
B+U0100-U02FF, U0028 00U0100-U02FF, U0028 00
IgnitionU0100-U02FF, U1814 02, U2099 02, U0028 00U0100-U02FF, U0028 00
MOST ControlU2098 00, U2098 02, U0029 02U0028 00U2098 00, U2098 02
MOST Bus Serial Data (+)U0028 00U0028 00U0028 00
MOST Bus Serial Data (-)U0028 00U0028 00U0028 00
GroundU0100-U02FF, U0028 00

The Media Oriented Systems Transport (MOST) Infotainment network is a dedicated high speed multimedia streaming data bus independent from GMLAN. The MOST bus will be configured in a physical hardwired loop with each device within the bus sends and receives data on an assigned MOST addresses in a set order. Each device on the MOST bus will be required to have twisted pair copper wires (2 transmit TX, 2 receive RX, and 1 electronic control line which is a 12 V wake up signal line). The A11 Radio is the MOST Master and will monitor the bus for vehicle configuration, Infotainment data messages and errors on the bus. The MOST initialization consists of a short 100 ms low voltage pulse on the electronic control line connected to all devices contained on the MOST ring. When the MOST devices receive this wakeup message, they will respond with a generic device response. Once these initial responses on the MOST bus are reported successfully without error to the A11 Radio, the next responses will report the MOST device addresses, their functionality requirements and capabilities within. The A11 Radio will learn this information and also record the address node sequence on the MOST bus at this point. This node address list will now be stored within the A11 Radio as the MOST bus configuration (called "Last Working MOST ID of Node 1-9" on scan tool data display).

When MOST receive, transmit, or control line faults are detected, transmit/receive messages will not be received as expected from the wakeup request. The A11 Radio and the K74 Human Machine Interface Control Module will then perform diagnostics to isolate these MOST faults. If the MOST control line is shorted low to 0 V for excess amount of time, the A11 Radio will set a U2098 DTC and K74 Human Machine Interface Control Module will set a U0029 02 DTC. At this point the MOST bus will be unable to communicate until the shorted MOST control line is repaired.

Once the shorted MOST control line diagnostics pass, the A11 Radio will attempt to resend the initial short pulse attempts up to 3 times on the MOST control line. If the expected responses are not received, the A11 Radio continues into a failure mode setting a U0028 DTC and will continue on to send 300 ms long pulses while DTC U0028 is current, which will enable the furthest upstream transmitting device to become the surrogate MOST Master in this MOST fault/diagnostic mode. When the A11 Radio receives this new MOST Master identity, the surrogate MOST master device can be identified based on scan tool data parameter "Surrogate MOST Master Node Upstream Position". The scan tool and schematics will be used to determine the MOST bus configuration and direction by utilizing the "Last Working MOST ID of Node 1 - 9" parameters from the A11 Radio data display. When a fault is present, it will indicate the newly enabled "Surrogate MOST Master Node Upstream Position" to the A11 Radio. This will assist in determining the location of the MOST device/bus/control fault. The MOST device and circuits upstream from the surrogate MOST master device, transmit, receive, or control lines will be the suspect areas for diagnostics at this point. These faults can be associated with any of the MOST transmit, receive, or control line twisted copper wires or possibly an internal device fault.

  1. The system voltage is between 9-16 V.
  2. The ignition is ON.
  3. The Radio is ON.

A fault occurs on the transmit, receive, electronic control lines, or internal device.

Some or all of the infotainment system audio and displays may be inoperative.

The MOST initialization is successful without errors and the MOST bus is locked.

  1. Use A11 Radio's scan tool data display to determine the MOST device location IDs and the MOST bus configuration from "Last Working MOST ID of Node 1-9" parameters.
  2. The Last Working MOST ID of Node 1-9 may be lost and reset to None after an ignition cycle when there is a fault on the MOST bus. In this case, use the MOST bus configuration from the schematics and eliminate optional devices that are not available for a particular vehicle from that configuration. Each vehicle may have a different MOST bus configuration depending on the optional contents.
  3. Use A11 Radio's scan tool data display to determine the surrogate MOST Master device and where the MOST ring break occurs by interpreting the "Surrogate MOST Master Node Upstream Position" parameter. When there is no MOST bus fault, this value is None.
  4. Always determine the correct MOST bus configuration prior to diagnosing the MOST bus fault. Below is an example of using the "Surrogate MOST Master Node Upstream Position" parameter to find the fault location. Keep in mind that each vehicle may have a different MOST bus configuration and may not be the same as the following configuration. This example is used to help understand the diagnostic strategy of the MOST bus: For example, if the MOST bus configuration is A11 Radio > T3 Audio Amplifier > P16 Instrument Cluster > A33 Media Disc Player > K74 Human Machine Interface Control Module and back to A11 Radio, the A11 Radio's scan tool data display will be shown as followed: Last Working MOST ID of Node 1: Radio Last Working MOST ID of Node 2: Audio Amplifier Last Working MOST ID of Node 3: Instrument Cluster Last Working MOST ID of Node 4: Media Disc Player Last Working MOST ID of Node 5: Human Machine Interface Control Module After a ring break diagnostic session, the A11 Radio, which is the MOST bus master, indicates a ring break was detected and sets DTC U0028. The "Surrogate MOST Master Node Upstream Position" parameter will now be available in the A11 Radio's scan tool data display. It will take approximately 10 s for the A11 Radio to assign the Surrogate MOST Master Node Upstream Position value. Starting from the bottom of the MOST device list, count upward to determine the surrogate MOST Master device. The MOST ring break will be found upstream from the surrogate MOST Master since this will be the node which timed out and initiated the MOST node assignments during the MOST ring break. If the Surrogate MOST Master Node Upstream Position value is 0, the Surrogate MOST Master is also the A11 Radio. The MOST ring break is either at the K74 Human Machine Interface Control Module or between the A11 Radio and the K74 Human Machine Interface Control Module. If the Surrogate MOST Master Node Upstream Position value is 1, the Surrogate MOST Master is the K74 Human Machine Interface Control Module which is 1 node upstream from the A11 Radio. The MOST ring break is either at the A33 Media Disc Player or between the K74 Human Machine Interface Control Module and the A33 Media Disc Player. If the Surrogate MOST Master Node Upstream Position value is 2, the Surrogate MOST Master is the A33 Media Disc Player which is 2 nodes upstream from the A11 Radio. The MOST ring break is either at the P16 Instrument Cluster or between the A33 Media Disc Player and the P16 Instrument Cluster. If the Surrogate MOST Master Node Upstream Position value is 3, the Surrogate MOST Master is the P16 Instrument Cluster which is 3 nodes upstream from the A11 Radio. The MOST ring break is either at the T3 Audio Amplifier or between the P16 Instrument Cluster and the T3 Audio Amplifier. If the Surrogate MOST Master Node Upstream Position value is 4, the Surrogate MOST Master is the T3 Audio Amplifier which is 4 nodes upstream from the A11 Radio. The MOST ring break is between the T3 Audio Amplifier and the A11 Radio.
  5. With the latest software, the A11 Radio will report the Surrogate MOST Master Node Upstream Position value when DTC U0028 is stored in history. The U0028 DTC state and the Number of MOST Communication Breaks parameter must be used with the Surrogate MOST Master Node Upstream Position parameter for a successful diagnosis. This is used to help capture surrogate information on intermittent fault conditions. The Number of MOST Communication Breaks counter will increase each time the MOST bus state transitions from Normal Operation (Lock status) to Off State (Unlock status) and will accumulate from 0-65535. After the Number of MOST Communication Breaks counter increases 10 times, DTC U0028 will be set.
  6. It is important to clear DTC U0028 and reset the Surrogate MOST Master Node Upstream Position value to None after a successful repair. The Surrogate MOST Master Node Upstream Position value can be reset to None by disconnecting the A11 Radio power, disconnecting the battery cables, or after 50 ignition power down cycles. This will also reset the Number of MOST Communication Breaks counter to 0.
  7. An open in the MOST control line or a fault in the MOST transmit/receive lines will cause DTC U0028 to be set.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON. Radio ON.
  2. Verify DTC U0100-U02FF is set. If the DTC is set Refer to «DTC U0100-U02FF»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) . If the DTC is not set
  3. Verify DTC U2098 or DTC U0029 02 is set. If any of the DTCs are set Refer to «DTC U2098»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) . If none of the DTCs are set
  4. Verify DTC U0028 is set. If the DTC is set as a current DTC Access the A11 Radio's Last Working MOST ID of Node 1-9 parameters with a scan tool to view MOST device location IDs and MOST bus configuration. Access the A11 Radio's Surrogate MOST Master Node Upstream Position parameter with a scan tool to determine the surrogate MOST Master device and where the MOST ring break occurs. For more information, refer to Diagnostic Aids section. Refer to Circuit/System Testing. If the DTC U0028 is set as a history DTC along with other DTCs set Diagnose all other DTCs first. Refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) . If the DTC U0028 is set as a history DTC with audio or display malfunction and without other DTCs set Access the A11 Radio scan tool data display to record the value of the Surrogate MOST Master Node Upstream Position and the Number of MOST Communication Breaks parameters. Refer to Diagnostic Aids section to help determine the MOST bus configuration, the surrogate MOST Master device and where the MOST ring break occurs to assist in the isolation of intermittent condition. Refer to Circuit/System Testing. If the DTC U0028 is not set
  5. Refer to Repair Verification.

Circuit/System Testing

Note. The MOST devices on both sides of the MOST ring break point will need to be disconnected to isolate a circuit fault. Use the schematic to identify the following: The MOST bus configuration and MOST device locations on the MOST serial data circuits Each MOST device's electronic control line and serial data circuit terminals

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down. Disconnect the harness connectors at the MOST device upstream from the surrogate MOST Master device where the MOST ring break occurs.
  2. Test for less than 10 ohms between each ground circuit terminal and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  3. Ignition ON.
  4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the disconnected device. If the test lamp illuminates
  5. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is OK and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the disconnected device. If the test lamp illuminates
  6. Test for 9-13 V between the MOST control circuit at the MOST device connectors that was just disconnected and ground. If less than 9 V Ignition OFF, disconnect the harness connectors at the A11 Radio. Test for less than 2 ohms in the MOST control circuit end to end between the MOST device that was just disconnected and the A11 Radio. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the A11 Radio. If greater than 13 V Ignition OFF, disconnect the harness connectors at the A11 Radio. Test for less than 1 V between the MOST control circuit and ground. If 1 V or greater, repair the short to voltage in the circuit. If less than 1 V, replace the A11 Radio. If between 9-13 V
  7. Ignition OFF, disconnect the harness connectors at the surrogate MOST Master device, ignition ON. The following tests will be performed on the MOST serial data circuits between the two MOST devices that were just disconnected.
  8. Test for less than 1 V between each MOST serial data circuit and ground. If any serial data circuit are 1 V or greater Repair the short to voltage in the circuit. If each serial data circuit are less than 1 V
  9. Ignition OFF, test for infinite resistance between each MOST serial data circuit and ground. If any serial data circuit are less than infinite resistance Repair the short to ground in the circuit. If each serial data circuit are infinite resistance
  10. Test for infinite resistance between each pair of the MOST serial data circuits. If any pair of serial data circuits are less than infinite resistance Repair a short together in the circuit. If each pair of serial data circuits are infinite resistance
  11. Test for less than 2 ohms in each MOST serial data circuit end to end. If any serial data circuit are 2 ohms or greater Repair the open/high resistance in the circuit between the two MOST devices. If each serial data circuit are less than 2 ohms
  12. Replace the MOST device upstream from the surrogate MOST Master device where the MOST ring break occurs.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup

Repair Verification

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down.
  2. Ignition ON.
  3. Access the A11 Radio scan tool data display and verify that the Surrogate MOST Master Node Upstream Position parameter value is None. If the value is not None Disconnect the A11 Radio power or the battery cables to reset this value to None. If the value is None
  4. All OK.
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

The Media Oriented Systems Transport (MOST) bus master device shall set DTC U0029 when the MOST bus interruptions lasts long enough to interrupt MOST communication and functions, but not long enough to break the MOST bus ring.

  1. The system voltage is between 9-16 V.
  2. The ignition is ON.
  3. The Radio is ON.

A current DTC sets when MOST bus communication has been interrupted more than 10 times during the monitoring cycle period.

Some or all of the infotainment system may be inoperative for brief periods of time.

A current DTC is cleared when MOST bus communication interruptions are no longer detected and the Number of MOST Communication Breaks counter remains at 0.

This is an intermittent connection detection DTC. All MOST device connectors should be checked for poor connections on both MOST bus circuits.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON. Radio ON.
  2. Verify DTC U0028 is set. If the DTC is set Refer to «DTC U0028»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) . If the DTC is not set
  3. Verify DTC U0029 is not set with symptom byte 02. If DTC U0029 is set with symptom byte 02 Refer to «DTC U2098»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) . If DTC U0029 is set with other symptom bytes except 02
  4. Refer to «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor) to test for an intermittent condition.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

The serial data circuits are used to communicate information between the devices. The serial data circuits also connect directly to the data link connector (DLC).

  1. Supply voltage to the devices is in the normal operating range.
  2. The vehicle power mode requires serial data communications.

The device setting the DTC has attempted to establish communications on the serial data circuits more than 3 times in 5 s.

  1. The device suspends all message transmission.
  2. The device uses default values for all parameters received on the serial data circuits.
  3. In the transmission control module, DTC U0073 will cause the transmission to go into default gears.
  4. In the engine control module and transmission control module, DTC U0073 will cause the malfunction indicator lamp (MIL) to illuminate.
  5. If equipped with eAssist, DTC U0073 in the hybrid powertrain control module is a type B DTC and will cause the malfunction indicator lamp to illuminate and result in the engine operating in conventional engine mode and will maintain 14 V module operation.
  6. The device inhibits the setting of all other communication DTCs.
  1. The engine control module or transmission control module turns OFF the MIL after 4 consecutive ignition cycles that the diagnostic runs and does not fail.
  2. If equipped with eAssist, the hybrid powertrain control module turns off the MIL after the diagnostic runs and does not fail during subsequent ignition cycles. Normal operation will resume 5 s after subsequent ignition cycle.
  3. A current DTC clears when the malfunction is no longer present.
  4. A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.
  1. Refer to «Data Link References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__data-link-references) to determine which serial data communication system is used for a specific device.
  2. This DTC may not be retrieved with a current status. Diagnosis is accomplished using the symptom. Refer to «Symptoms - Data Communications»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__symptoms-data-communications) .
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Chassis High Speed GMLAN Serial Data (+)U0074U0074, U0100-U02FF*U0074
Chassis High Speed GMLAN Serial Data (-)U0074U0074, U0100-U02FF*U0074
Ground (DLC, terminal 5)1
* An open between the data link connector (DLC) and the first splice/device will only affect the communication with the scan tool. The devices will still communicate. An open in only one chassis high speed GMLAN serial data circuit may allow degraded communication between the devices. 1. No communication with any chassis high speed GMLAN device.

The devices connected to the chassis high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices when the ignition switch is in any position other than OFF. The chassis high speed GMLAN serial data bus uses terminating resistors that are in parallel with the chassis high speed GMLAN (+) and (-) circuits.

The system voltage is between 9-16 V.

A supervised periodic message that includes the transmitter device availability has not been received.

Specific subsystems will not function.

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.
  1. Use the «Data Link References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__data-link-references) to identify the chassis high speed GMLAN devices.
  2. Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of-communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios: A device on the data communication circuit was disconnected while the communication circuit is awake. Power to one or more devices was interrupted during diagnosis. A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold. Battery power was restored to the vehicle and devices on the communication circuit did not all re-initialize at the same time. If a loss-of-communication U code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
  3. Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.
  4. Communication may be available between some devices and the scan tool with the chassis high speed GMLAN serial data system inoperative. This condition is due to those devices using multiple serial data communication systems.
  5. An open in the DLC ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle.
  6. Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC).
  7. Some devices may not have internal protection for specific voltage outputs and may open a battery positive voltage or ignition voltage source fuse. If a voltage input fuse is open and no short is found in that circuit, ensure that no device output voltage circuit is shorted to ground before replacing the device.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify two or more devices are not communicating on the chassis high speed GMLAN serial data circuit. Refer to «Data Link References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__data-link-references) to determine how many devices should be communicating on the bus. If only one device is not communicating Refer to Circuit/System Testing - Testing the Device Circuits. If two or more devices are not communicating
  3. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the scan tool from the X84 Data Link Connector. The following tests will be done at the X84 Data Link Connector. It may take up to 2 minutes for all vehicle systems to power down.
  4. Test for less than 10 ohms between the ground circuit terminal 5 and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  5. Ignition ON.
  6. Test for less than 4.5 V between the serial data circuits listed below and ground: Chassis high speed GMLAN serial data terminal 12 Chassis high speed GMLAN serial data terminal 13 If 4.5 V or greater Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Voltage. If less than 4.5 V
  7. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  8. Test for greater than 100 ohms between the serial data circuits listed below and ground: Chassis high speed GMLAN serial data terminal 12 Chassis high speed GMLAN serial data terminal 13 If 100 ohms or less Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Ground. If greater than 100 ohms
  9. Test for 50-70 ohms between the serial data circuit terminals 12 and 13: If less than 35 ohms Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short between the Circuits. If between 35-50 ohms There may be a third terminating resistor between the serial data circuits. This can happen if the incorrect device is installed. Some devices are available with and without the terminating resistors installed to reduce the need of terminating resistors in the wiring harness. Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short between the Circuits. If greater than 70 ohms but less than infinite Refer to Circuit/System Testing - Testing the Serial Data Circuits for an Open/High Resistance. If infinite resistance Repair the open/high resistance in the circuit between the X84 Data Link Connector and the first splice/device in the serial data circuit. If between 50-70 ohms
  10. Refer to Circuit/System Testing - Testing the Device Circuits.

Note. Each device may need to be disconnected to isolate a circuit fault. Use the schematic to identify the following: Chassis high speed GMLAN devices the vehicle is equipped with Chassis high speed GMLAN serial data circuit terminating resistors Device locations on the chassis high speed GMLAN serial data circuits Each device's ground, B+, ignition, and chassis high speed GMLAN serial data circuit terminals Some devices with an internal terminating resistor have a loop in the harness that connects the internal terminating resistor to the serial data circuit. When wired this way, test these loop circuits for the appropriate failure mode short to voltage, short to ground, or open/high resistance prior to replacing the device for each of the following tests.

Testing the Serial Data Circuits for a Short to Voltage

  1. Ignition OFF, disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at an easily accessible device, ignition ON.
  2. Test for greater than 4.5 V between each serial data circuit at the device connector that was just disconnected and ground. If each serial data circuit is 4.5 V or less Ignition OFF. Test for less than 10 ohms between each of the device's ground circuit terminals and ground. If 10 ohms or greater, repair the open/high resistance in the circuit. If less than 10 ohms, replace the device that was disconnected. If any serial data circuit is greater than 4.5 V
  3. Ignition OFF, disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted to voltage, ignition ON.
  4. Test for greater than 4.5 V between each serial data circuit at the device connector that was just disconnected and ground. If each serial data circuit is 4.5 V or less Ignition OFF. Test for less than 10 ohms between each of the device's ground circuit terminals and ground. If 10 ohms or greater, repair the open/high resistance in the circuit. If less than 10 ohms, replace the device that was disconnected. If any serial data circuit is greater than 4.5 V
  5. Repeat step 3 until one of the following conditions are isolated: A short to voltage on the serial data circuit between two devices or splice packs, if equipped. A short to voltage on the serial data circuit between a device and a terminating resistor.

Testing the Serial Data Circuits for a Short to Ground

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at an easily accessible device.
  3. Test for greater than 100 ohms between each serial data circuit at the device connector that was just disconnected and ground. If each serial data circuit is 100 ohms or greater Replace the device that was disconnected. If any serial data circuit is less than 100 ohms
  4. Disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted to ground.
  5. Test for greater than 100 ohms between each serial data circuit at the device connector that was just disconnected and ground. If both serial data circuits are 100 ohms or greater Replace the device that was disconnected. If any serial data circuit is less than 100 ohms
  6. Repeat step 4 until one of the following conditions are isolated: A short to ground on the serial data circuit between two devices or splice packs, if equipped. A short to ground on the serial data circuit between a device and a terminating resistor. A short to ground on the serial data circuit between the X84 Data Link Connector and the first device or splice pack.

Testing the Serial Data Circuits for a Short between the Circuits

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at an easily accessible device that is not communicating.
  3. Test for greater than 110 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 110 ohms or greater Replace the device that was disconnected. If any pair of serial data circuits is less than 110 ohms
  4. Connect the harness connectors at the device that was disconnected.
  5. Disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted together.
  6. Test for greater than 110 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 110 ohms or greater Replace the device that was disconnected. If any pair of serial data circuits is less than 110 ohms
  7. Repeat step 4 until one of the following conditions are isolated: Serial data circuits shorted together between two devices or splice packs, if equipped. Serial data circuits shorted together between a device and a terminating resistor. Serial data circuits shorted together between the X84 Data Link Connector and the first device or splice pack. A shorted terminating resistor.

Testing the Serial Data Circuits for an Open/High Resistance

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at an easily accessible device that is not communicating.
  3. Test for less than 130 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 130 ohms or less Replace the device that was disconnected. If any pair of serial data circuits is greater than 130 ohms
  4. Connect the harness connectors at the device that was disconnected.
  5. Disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at another device, in the direction of the circuit with the open/high resistance.
  6. Test for less than 130 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 130 ohms or less Replace the device that was disconnected. If any pair of serial data circuits is greater than 130 ohms
  7. Repeat step 4 until one of the following conditions are isolated: An open/high resistance on the serial data circuit between two devices or splice packs, if equipped. An open/high resistance on the serial data circuit between a device and a terminating resistor. An open/high resistance terminating resistor.

Testing the Device Circuits

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors at an easily accessible device that is not communicating.
  3. Test for less than 10 ohms between each ground circuit terminal and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the disconnected device. If the test lamp illuminates
  5. Ignition ON.
  6. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which has a fuse in the circuit, and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is OK and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the disconnected device. If the test lamp illuminates
  7. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which is controlled by a control module, and ground. If the test lamp does not illuminate Ignition OFF, disconnect the harness connectors at the control module that controls the ignition circuit. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the control module that controls the ignition circuit. If the test lamp illuminates
  8. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  9. Test for less than 130 ohms between each pair of chassis high speed GMLAN serial data circuits at the device connector that was just disconnected. If any pair of serial data circuits is greater than 130 ohms Repair the open/high resistance in the serial data circuits between the disconnected device and the circuit splice in the serial data circuits. If each pair of serial data circuits is 130 ohms or less
  10. Replace the device that was disconnected.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Object Detection High Speed GMLAN Serial Data (+)U0075U0075, U0100-U02FF*U0075
Object Detection High Speed GMLAN Serial Data (-)U0075U0075, U0100-U02FF*U0075
Ground (DLC, terminal 5)1
* An open between the data link connector (DLC) and the first splice/device will only affect the communication with the scan tool. The devices will still communicate. An open in only one object detection high speed GMLAN serial data circuit may allow degraded communication between the devices. 1. No communication with any object detection high speed GMLAN device.

The devices connected to the object detection high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices when the ignition switch is in any position other than OFF. The object detection high speed GMLAN serial data bus uses terminating resistors that are in parallel with the object detection high speed GMLAN (+) and (-) circuits.

The system voltage is between 9-16 V.

A supervised periodic message that includes the transmitter device availability has not been received.

Specific subsystems will not function.

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.
  1. Use the «Data Link References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__data-link-references) to identify the object detection high speed GMLAN devices.
  2. Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of-communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios: A device on the data communication circuit was disconnected while the communication circuit is awake. Power to one or more devices was interrupted during diagnosis. A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold. Battery power was restored to the vehicle and devices on the communication circuit did not all re-initialize at the same time. If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
  3. Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.
  4. Communication may be available between some devices and the scan tool with the object detection high speed GMLAN serial data system inoperative. This condition is due to those devices using multiple serial data communication systems.
  5. An open in the DLC ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle.
  6. Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC).
  7. Some devices may not have internal protection for specific voltage outputs and may open a battery positive voltage or ignition voltage source fuse. If a voltage input fuse is open and no short is found in that circuit, ensure that no device output voltage circuit is shorted to ground before replacing the device.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify two or more devices are not communicating on the object detection high speed GMLAN serial data circuit. Refer to «Data Link References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__data-link-references) to determine how many devices should be communicating on the bus. If only one device is not communicating Refer to Circuit/System Testing - Testing the Device Circuits. If two or more devices are not communicating
  3. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the scan tool from the X84 data link connector. The following tests will be done at the X84 data link connector. It may take up to 2 minutes for all vehicle systems to power down.
  4. Test for less than 10 ohms between the ground circuit terminal 5 and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  5. Ignition ON.
  6. Test for less than 4.5 V between the serial data circuits listed below and ground: Object detection high speed GMLAN serial data terminal 3 Object detection high speed GMLAN serial data terminal 11 If 4.5 V or greater Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Voltage. If less than 4.5 V
  7. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  8. Test for greater than 100 ohms between the serial data circuits listed below and ground: Object detection high speed GMLAN serial data terminal 3 Object detection high speed GMLAN serial data terminal 11 If 100 ohms or less Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Ground. If greater than 100 ohms
  9. Test for 50-70 ohms between the serial data circuit terminals 3 and 11: If less than 35 ohms Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short between the Circuits. If between 35-50 ohms There may be a third terminating resistor between the serial data circuits. This can happen if the incorrect device is installed. Some devices are available with and without the terminating resistors installed to reduce the need of terminating resistors in the wiring harness. Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short between the Circuits. If greater than 70 ohms but less than infinite Refer to Circuit/System Testing - Testing the Serial Data Circuits for an Open/High Resistance. If infinite resistance Repair the open/high resistance in the circuit between the X84 data link connector and the first splice/device in the serial data circuit. If between 50-70 ohms
  10. Refer to Circuit/System Testing - Testing the Device Circuits.

Note. Each device may need to be disconnected to isolate a circuit fault. Use the schematic to identify the following: Object detection high speed GMLAN devices the vehicle is equipped with Object detection high speed GMLAN serial data circuit terminating resistors Device locations on the object detection high speed GMLAN serial data circuits Each device's ground, B+, ignition, and object detection high speed GMLAN serial data circuit terminals Some devices with an internal terminating resistor have a loop in the harness that connects the internal terminating resistor to the serial data circuit. When wired this way, test these loop circuits for the appropriate failure mode short to voltage, short to ground, or open/high resistance prior to replacing the device for each of the following tests.

Testing the Serial Data Circuits for a Short to Voltage

  1. Ignition OFF, disconnect the harness connectors with the object detection high speed GMLAN serial data circuits at an easily accessible device, ignition ON.
  2. Test for greater than 4.5 V between each serial data circuit at the device connector that was just disconnected and ground. If each serial data circuit is 4.5 V or less Ignition OFF. Test for less than 10 ohms between each of the device's ground circuit terminals and ground. If 10 ohms or greater, repair the open/high resistance in the circuit. If less than 10 ohms, replace the device that was disconnected. If any serial data circuit is greater than 4.5 V
  3. Ignition OFF, disconnect the harness connectors with the object detection high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted to voltage, ignition ON.
  4. Test for greater than 4.5 V between each serial data circuit at the device connector that was just disconnected and ground. If each serial data circuit is 4.5 V or less Ignition OFF. Test for less than 10 ohms between each of the device's ground circuit terminals and ground. If 10 ohms or greater, repair the open/high resistance in the circuit. If less than 10 ohms, replace the device that was disconnected. If any serial data circuit is greater than 4.5 V
  5. Repeat step 3 until one of the following conditions are isolated: A short to voltage on the serial data circuit between two devices or splice packs, if equipped. A short to voltage on the serial data circuit between a device and a terminating resistor.

Testing the Serial Data Circuits for a Short to Ground

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors with the object detection high speed GMLAN serial data circuits at an easily accessible device.
  3. Test for greater than 100 ohms between each serial data circuit at the device connector that was just disconnected and ground. If each serial data circuit is 100 ohms or greater Replace the device that was disconnected. If any serial data circuit is less than 100 ohms
  4. Disconnect the harness connectors with the object detection high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted to ground.
  5. Test for greater than 100 ohms between each serial data circuit at the device connector that was just disconnected and ground. If both serial data circuits are 100 ohms or greater Replace the device that was disconnected. If any serial data circuit is less than 100 ohms
  6. Repeat step 4 until one of the following conditions are isolated: A short to ground on the serial data circuit between two devices or splice packs, if equipped. A short to ground on the serial data circuit between a device and a terminating resistor. A short to ground on the serial data circuit between the X84 DLC and the first device or splice pack.

Testing the Serial Data Circuits for a Short between the Circuits

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors with the object detection high speed GMLAN serial data circuits at an easily accessible device that is not communicating.
  3. Test for greater than 110 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 110 ohms or greater Replace the device that was disconnected. If any pair of serial data circuits is less than 110 ohms
  4. Connect the harness connectors at the device that was disconnected.
  5. Disconnect the harness connectors with the object detection high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted together.
  6. Test for greater than 110 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 110 ohms or greater Replace the device that was disconnected. If any pair of serial data circuits is less than 110 ohms
  7. Repeat step 4 until one of the following conditions are isolated: Serial data circuits shorted together between two devices or splice packs, if equipped. Serial data circuits shorted together between a device and a terminating resistor. Serial data circuits shorted together between the X84 data link connector and the first device or splice pack. A shorted terminating resistor.

Testing the Serial Data Circuits for an Open/High Resistance

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors with the object detection high speed GMLAN serial data circuits at an easily accessible device that is not communicating.
  3. Test for less than 130 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 130 ohms or less Replace the device that was disconnected. If any pair of serial data circuits is greater than 130 ohms
  4. Connect the harness connectors at the device that was disconnected.
  5. Disconnect the harness connectors with the object detection high speed GMLAN serial data circuits at another device, in the direction of the circuit with the open/high resistance.
  6. Test for less than 130 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 130 ohms or less Replace the device that was disconnected. If any pair of serial data circuits is greater than 130 ohms
  7. Repeat step 4 until one of the following conditions are isolated: An open/high resistance on the serial data circuit between two devices or splice packs, if equipped. An open/high resistance on the serial data circuit between a device and a terminating resistor. An open/high resistance terminating resistor.

Testing the Device Circuits

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors at an easily accessible device that is not communicating.
  3. Test for less than 10 ohms between each ground circuit terminal and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the disconnected device. If the test lamp illuminates
  5. Ignition ON.
  6. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which has a fuse in the circuit, and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is OK and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the disconnected device. If the test lamp illuminates
  7. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which is controlled by a control module, and ground. If the test lamp does not illuminate Ignition OFF, disconnect the harness connectors at the control module that controls the ignition circuit. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the control module that controls the ignition circuit. If the test lamp illuminates
  8. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  9. Test for less than 130 ohms between each pair of object detection high speed GMLAN serial data circuits at the device connector that was just disconnected. If any pair of serial data circuits is greater than 130 ohms Repair the open/high resistance in the serial data circuits between the disconnected device and the circuit splice in the serial data circuits. If each pair of serial data circuits is 130 ohms or less
  10. Replace the device that was disconnected.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Chassis High Speed GMLAN Serial Data (+)U0077U0077, U0100-U02FF*U0077
Chassis High Speed GMLAN Serial Data (-)U0077U0077, U0100-U02FF*U0077
Ground (DLC, terminal 5)1
* An open between the data link connector (DLC) and the first splice/device will only affect the communication with the scan tool. The devices will still communicate. An open in only one chassis high speed GMLAN serial data circuit may allow degraded communication between the devices. 1. No communication with any chassis high speed GMLAN device.

The devices connected to the chassis high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices when the ignition switch is in any position other than OFF. The chassis high speed GMLAN serial data bus uses terminating resistors that are in parallel with the chassis high speed GMLAN (+) and (-) circuits.

The system voltage is between 9-16 V.

A supervised periodic message that includes the transmitter device availability has not been received.

Specific subsystems will not function.

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.
  1. Use the «Data Link References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__data-link-references) to identify the chassis high speed GMLAN devices.
  2. Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of-communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios: A device on the data communication circuit was disconnected while the communication circuit is awake. Power to one or more devices was interrupted during diagnosis. A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold. Battery power was restored to the vehicle and devices on the communication circuit did not all re-initialize at the same time. If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
  3. Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.
  4. Communication may be available between some devices and the scan tool with the chassis high speed GMLAN serial data system inoperative. This condition is due to those devices using multiple serial data communication systems.
  5. An open in the DLC ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle.
  6. Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC).
  7. Some devices may not have internal protection for specific voltage outputs and may open a battery positive voltage or ignition voltage source fuse. If a voltage input fuse is open and no short is found in that circuit, ensure that no device output voltage circuit is shorted to ground before replacing the device.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify DTC U0077 is not set. If DTC U0077 is set Refer to «Scan Tool Does Not Communicate with Chassis High Speed GMLAN Device»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) . If DTC U0077 is not set
  3. All OK

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

The low speed GMLAN serial data bus is used to communicate information between the devices. The serial data is transmitted over a single wire to the appropriate devices. The low speed GMLAN serial data circuits also connect directly to the data link connector (DLC).

  1. Supply voltage to the devices are in the normal operating range.
  2. The vehicle power mode requires serial data communications.

The device setting the DTC has attempted to establish communications on the serial data circuits more than 3 times in 5 s.

  1. The device suspends all message transmission.
  2. The device uses default values for all parameters received on the serial data circuits.
  3. The device inhibits the setting of all other communication DTCs.
  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.
  1. Ignition ON.
  2. Verify DTC U0078 is not set. If DTC U0078 is set Refer to «Scan Tool Does Not Communicate with Low Speed GMLAN Device»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) . If DTC U0078 is not set
  3. All OK
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For device DTC descriptors, refer to Control Module U Code List .

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
B+U0100-U02FFU0100-U02FF
IgnitionU0100-U02FF, U1814, U2099U0100-U02FF
Object High Speed GMLAN Serial Data (+)U0075U0100-U02FFU0075
Object High Speed GMLAN Serial Data (-)U0075U0100-U02FFU0075
Chassis High Speed GMLAN Serial Data (+)U0074, U0077U0100-U02FFU0074, U0077
Chassis High Speed GMLAN Serial Data (-)U0074, U0077U0100-U02FFU0074, U0077
Mid Speed GMLAN Serial Data (+)U0074U0100-U02FFU0074
Mid Speed GMLAN Serial Data (-)U0074U0100-U02FFU0074
High Speed GMLAN Serial Data (+)U0073, 2U0100-U02FFU0073, 2
High Speed GMLAN Serial Data (-)U0073, 2U0100-U02FFU0073, 2
Low Speed GMLAN Serial DataU0078, 1U0100-U02FFU0078, 1
GroundU0100-U02FF
1. Scan tool does not communicate with most low speed GMLAN device 2. Scan tool does not communicate with most high speed GMLAN device

The serial data circuit is the means by which the devices in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the Data Link Connector (DLC), the scan tool can be used to monitor each device for diagnostic purposes and to check for Diagnostic Trouble Codes (DTC). When the ignition switch is in RUN, each device communicating on the serial data circuit sends a state of health message to ensure that the device is operating properly. When a device stops communicating on the serial data circuit, for example if the device loses power or ground, the state of health message it normally sends on the serial data circuit disappears. Other devices on the serial data circuit, which expect to receive that state of health message, detect its absence; those devices in turn set a DTC associated with the loss of state of health of the non-communicating device. The DTC is unique to the device which is not communicating and one or more devices may set the same exact code. A loss of serial data communications DTC does not represent a failure of the devices that contain the stored code.

The system voltage is between 9-16 V.

A supervised periodic message that includes the transmitter device availability has not been received.

  1. Specific subsystems will not function.
  2. DTC U0100 in the Transmission Control Module will cause the transmission to go into default gears.
  3. Both DTC U0100 in the Transmission Control Module and DTC U0101 in the Engine Control Module will cause the malfunction indicator lamp (MIL) to illuminate.
  1. The Engine Control Module or Transmission Control Module turns OFF the MIL after 4 consecutive ignition cycles that the diagnostic runs and does not fail.
  2. A current DTC clears when the malfunction is no longer present.
  3. A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.
  1. Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U code present. However, there is no associated "current" or "active" status. Loss of communication U codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios: A device on the data communication circuit was disconnected while the communication circuit is awake. Power to one or more devices was interrupted during diagnosis. A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold. Battery power was restored to the vehicle and devices on the communication circuit did not all re-initialize at the same time. If a loss of communication U code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
  2. A device may have a U code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U code.
  3. Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.
  4. Communication may be available between some devices and the scan tool with either the low or high speed GMLAN serial data system inoperative. This condition is due to those devices using multiple serial data communication systems.
  5. Use «Data Link References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__data-link-references) to determine what serial data communications the device uses.
  6. Some devices may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the device.
  7. Some intermittent communication concerns may be caused by fretting corrosion on the serial data circuit terminals. Inspect all connectors at the device that set the communication DTC, the device that the communication DTC was set against, and any inline harness connectors between the two devices. Do not replace a device based only on fretting corrosion. Refer to bulletin 09-06-03-004 for assistance with the diagnosis and repair of this condition, if applicable.
  8. This diagnostic can be used for any device that is not communicating, regardless of the type of serial data circuit it is connected to, providing the vehicle is equipped with the device.
  9. This diagnostic procedure can be used to diagnose the common no communication DTCs: U0100, U0101, U0102, U0103, U0104, U0105, U0106, U0109, U010E, U010F, U0111, U0112, U0115, U0117, U0121, U0122, U0123, U0125, U0126, U0128, U0129, U012A, U0130, U0131, U0132, U0133, U0136, U0137, U0139, U0140, U0146, U0151, U0155, U0158, U0159, U0160, U0164, U0166, U0167, U0168, U016B, U0170, U0181, U0182, U0184, U0186, U0191, U0193, U0196, U0197, U0198, U0201, U0203, U0204, U0207, U0208, U0209, U0210, U0230, U0232, U0233, U0236, U0237, U023A, U0248, U0249, U0250, U0252, U0254, U025B, U0264, U0265, U0268, U0269, U026A, U026B, U0293, U029D, U029E, U02A3, and other DTCs within U0100-U02FF range.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Determine the device that is not communicating. Refer to «Control Module U Code List»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__control-module-u-code-list) .
  2. Verify that DTC U0073, U2100, U0074, U0078, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not set. If any of the DTCs are set Refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) . If none of the DTCs are set
  3. Verify that DTC U0125 and DTC U0126 are not set together. If both of the DTCs are set together Refer to «Scan Tool Does Not Communicate with Chassis High Speed GMLAN Device»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) . If both of the DTCs are not set together
  4. Refer to Circuit/System Testing.

Note. Use the schematics and connector end views to identify the device's ground, B+, ignition, accessory wakeup serial data, serial data communication enable, and serial data circuit terminals.

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down. Disconnect all the harness connectors at the device that is not communicating.
  2. Test for less than 10 ohms between each ground circuit terminal and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  3. Ignition ON.
  4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF, remove the test lamp. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF, remove the test lamp. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the disconnected device. If the test lamp illuminates
  5. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF, remove the test lamp. Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is OK and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF, remove the test lamp. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the disconnected device. If the test lamp illuminates
  6. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which is controlled by a control module, and ground. If the test lamp does not illuminate Ignition OFF, remove the test lamp, disconnect the harness connectors at the control module that controls the ignition circuit. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the control module that controls the ignition circuit. If the test lamp illuminates
  7. Test for less than 4.5 V between each GMLAN serial data circuit terminal and ground. If 4.5 V or greater between a low speed GMLAN serial data circuit and ground Refer to «Scan Tool Does Not Communicate with Low Speed GMLAN Device»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) to test for a short to voltage. If 4.5 V or greater between a high speed GMLAN serial data circuit and ground Refer to «Scan Tool Does Not Communicate with High Speed GMLAN Device»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) to test for a short to voltage. If less than 4.5 V
  8. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down.
  9. Test for greater than 100 ohms between each GMLAN serial data circuit terminal and ground. If 100 ohms or less between a low speed GMLAN serial data circuit and ground Refer to «Scan Tool Does Not Communicate with Low Speed GMLAN Device»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) to test for a short to ground. If 100 ohms or less between a high speed GMLAN serial data circuit and ground Refer to «Scan Tool Does Not Communicate with High Speed GMLAN Device»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) to test for a short to ground. If greater than 100 ohms
  10. Test for less than 2 ohms in each of the GMLAN serial data circuits end to end between the device harness connector and the X84 Data Link Connector terminals listed below. Low speed GMLAN serial data circuit terminal 1 High speed GMLAN serial data circuit terminal 6 or 14 Mid speed GMLAN serial data circuit terminal 3 or 11 Chassis high speed GMLAN serial data circuit terminal 12 or 13 Object high speed GMLAN serial data circuit terminal 3 or 11 If 2 ohms or greater Repair the open/high resistance in the serial data circuit between the non communicating device and the device setting the DTC or a serial data splice pack. If less than 2 ohms
  11. Test for 110-130 ohms between each pair of high speed GMLAN serial data circuits. If less than 110 ohms Refer to «Scan Tool Does Not Communicate with High Speed GMLAN Device»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) to test for a short to ground or a short between the serial data circuits. If greater than 130 ohms Refer to «Scan Tool Does Not Communicate with High Speed GMLAN Device»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) to test for an open/high resistance in the serial data circuit. If between 110-130 ohms
  12. Replace the device that is not communicating.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Some devices must be configured with specific software, serial numbers, vehicle options, or other information. If a device was not properly configured after installation that device may set the appropriate communication DTCs. No external circuit diagnosis is involved.

Battery voltage is between 9-16 V and data link communications operate normally.

The device is not configured properly.

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify DTC U0300-U0336 is not set. If DTC U0300-U0336 is set Program the device specified by the DTC descriptor. Verify the DTC does not set. If the DTC sets, replace the device specified by the DTC descriptor. If the DTC does not set All OK. If DTC U0300-U0336 is not set
  3. All OK

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup

  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Some devices are constantly receiving information from other devices through serial data communication network. The invalid data code will be set when a receiving device detects a discrepancy in information it receives from another device causing its integrity to be questioned. The symptom byte listed in the DTC Descriptor is for engineering reference only. No external circuit diagnosis is involved.

Battery voltage is between 9-16 V and data link communications operate normally.

The device is not configured properly.

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Engine running for 10 s.
  2. Ignition ON, engine OFF, verify DTC U0400-U05FF is not set. If DTC U0400-U05FF is set along with other DTCs set Diagnose all other DTCs first. Refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) . If DTC U0400-U05FF is set without other DTCs set Program the device specified by the DTC descriptor. Verify the DTC does not set. If the DTC sets, replace the appropriate device. If the DTC does not set All OK. If DTC U0400-U05FF is not set
  3. All OK

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup

  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For device DTC descriptors, refer to Control Module U Code List .

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
B+U1500-U15BFU1500-U15BF
IgnitionU1500-U15BFU1500-U15BF
LIN Serial DataU1500-U15BFU1500-U15BFU1500-U15BF
GroundU1500-U15BF

The serial data is transmitted over a Local Interconnect Network (LIN) single wire network circuit bus between a master control module and other LIN devices within a particular subsystem. If serial data communication is lost between any of the LIN devices on the LIN bus network, a no communication code against the non-communicating LIN device will be set. A master control module is the one that reports the non communication code.

The system voltage is between 9-16 V.

A supervised periodic message that includes the transmitter device availability has not been received.

Specific subsystems will not function.

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.
  1. Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U code present. However, there is no associated "current" or "active" status. Loss of communication U codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios: A device on the data communication circuit was disconnected while the communication circuit is awake. Power to one or more devices was interrupted during diagnosis. A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold. Battery power was restored to the vehicle and devices on the communication circuit did not all re-initialize at the same time. If a loss of communication U code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
  2. A device may have a U code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U code.
  3. Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.
  4. Communication will be available between the master control module and the scan tool if there is a loss of communications with any of the other LIN devices on the LIN bus network.
  5. Some devices may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the device.
  6. Some intermittent communication concerns may be caused by fretting corrosion on the serial data circuit terminals. Inspect all connectors at the device that set the communication DTC, the device that the communication DTC was set against, and any inline harness connectors between the two devices. Do not replace a device based only on fretting corrosion. Refer to bulletin 09-06-03-004 for assistance with the diagnosis and repair of this condition, if applicable.
  7. An open in the LIN bus serial data circuit between the splice pack and a LIN device will only affect that specific LIN device. This type of failure will set a loss of communication DTC for each LIN device affected and the other LIN devices will still communicate.
  8. This diagnostic procedure can be used to diagnose the common LIN DTCs: U1500, U1501, U1502, U1503, U1504, U1505, U1506, U1507, U1508, U1509, U150E, U150F, U1510, U1511, U1512, U1513, U1514, U1515, U1516, U1517, U1518, U1519, U151A, U151B, U151C, U1520, U1521, U1522, U1523, U1524, U1526, U1528, U152C, U152D, U1530, U1531, U1532, U1534, U1538, U153A, U1540, U1544, U1548, U1549, U154A, U154B, U1550, U1556, U1558, U15E1, U15E3, U15F0, and other DTCs within the U1500-U15FF range.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Determine the LIN device that is not communicating. Refer to «Control Module U Code List»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__control-module-u-code-list) .
  2. Verify that DTC B1325, B1330, B1370, B1380, B1424, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not set. If any of the DTCs are set Refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) . If none of the DTCs are set
  3. Verify that DTC U0100-U02FF is not set. If any of the DTCs are set Refer to «DTC U0100-U02FF»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) . If none of the DTCs are set
  4. Refer to Circuit/System Testing.

Note. For some vehicles, both headlamps may be connected to the same LIN circuit through a splice. Or both LIN circuits to the headlamps may be internally connected at the connector of the K26 Headlamp Control Module or K28 Headlamp Leveling Control Module. A short in one headlamp or its LIN circuit may cause no communication to both headlamps. Ensure to diagnose both LIN circuits and headlamps prior to replacing any headlamp. Use the schematic to identify the following: The master control module and the LIN devices on the same LIN serial data circuit The master control module's LIN serial data circuit terminal and the LIN device's B+, ignition, ground, and LIN serial data circuit terminals

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down. Disconnect the harness connector at a LIN device that is not communicating.
  2. Test for less than 10 ohms between each ground circuit terminal and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  3. Ignition ON.
  4. Verify a test lamp illuminates between each B+ circuit terminal and ground, if equipped. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF, remove the test lamp. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF, remove the test lamp. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the disconnected LIN device. If the test lamp illuminates
  5. Verify a test lamp illuminates between each ignition circuit terminal and ground, if equipped. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF, remove the test lamp. Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is OK and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF, remove the test lamp. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the disconnected LIN device. If the test lamp illuminates
  6. Verify a test lamp illuminates between each ignition circuit terminal, which is controlled by a control module, and ground, if equipped. If the test lamp does not illuminate Ignition OFF, remove the test lamp, disconnect the harness connectors at the control module that controls the ignition circuit. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the control module that controls the ignition circuit. If the test lamp illuminates
  7. Test for 2-13 V between the LIN serial data circuit terminal and ground. If less than 2 V Ignition OFF, remove the test lamp, disconnect the harness connector at the control module setting the DTC and all LIN devices that share the same LIN serial data circuit. Test for infinite resistance between the serial data circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the serial data circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms Reconnect the control module that set the DTC, ignition ON. Test for 2-13 V between the LIN serial data circuit terminal and ground. If less than 2 V, replace the control module setting the DTC. If greater than 2 V, replace the LIN device that causes a current DTC to set when connected. If greater than 13 V Ignition OFF, disconnect the harness connector at the control module setting the DTC and all LIN devices that share the same LIN serial data circuit. Ignition ON. Test for less than 1 V between the serial data circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Ignition OFF, reconnect the control module that set the DTC, ignition ON. Test for 2-13 V between the LIN serial data circuit terminal and ground. If greater than 13 V, replace the control module setting the DTC. If less than 13 V, replace the LIN device that causes a current DTC to set when connected. If between 2-13 V
  8. Replace the disconnected LIN device.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
IgnitionU1814 02*U0100-U02FF
* Vehicle may not start.

The body control module (BCM) activates the ignition circuit, when the ignition key is in ACC, ON or START. The ignition circuit wakes up the devices for serial data bus communication.

  1. The system voltage is between 9-16 V.
  2. The vehicle power mode master requires serial data communication to occur.

The BCM senses a short to ground on the ignition circuit.

  1. The output command is turned off while the malfunction is present.
  2. The devices use a default value for the missing parameters until the next ignition cycle.
  3. The device(s) is never signaled. Therefore, the specific subsystem(s) will not function.
  4. The vehicle will not start while the circuit is shorted to ground.
  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Note. Use the schematic to determine which devices are on the K9 Body Control Module's ignition circuit terminal 22 X4. Use the connector end view to identify the ignition circuit terminal for each of those devices.

  1. Ignition OFF, disconnect the harness connectors at an easily accessible device that shares the K9 Body Control Module's ignition circuit terminal 22 X4. Ignition ON.
  2. Verify that the DTC U1814 remains current. If the DTC becomes history Replace the device that was just disconnected. If the DTC remains current
  3. With the prior devices disconnected, repeat steps 1 and 2 for each device on the ignition circuit except the K9 Body Control Module.
  4. Ignition OFF, disconnect the X4 harness connector at the K9 Body Control Module.
  5. Test for infinite resistance between the ignition circuit terminal 22 X4 at the K9 Body Control Module and ground. If less than infinite resistance Repair the short to ground on the circuit. If infinite resistance
  6. Replace the K9 Body Control Module.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
B+U0121, U0129, U1833U0121, U0129, U1833
IgnitionU0121, U0129, U1833U0121, U0129, U1833
Serial Data Communication EnableU1814, U2099U0121, U0129, U1833
Chassis High Speed GMLAN Serial Data (+)U0077*U0077*U0077*
Chassis High Speed GMLAN Serial Data (-)U0077*U0077*U0077*
GroundU0121, U0129, U1833
* Other DTCs may set with this fault.

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device.

The system voltage is at least 10 V.

A supervised periodic message that includes the transmitter device availability has not been received.

  1. A driver information center message and/or a warning indicator may be displayed.
  2. The DTC U1833 is a type B DTC.

The DTC U1833 is a type B DTC.

  1. Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U code present. However, there is no associated "current" or "active" status. Loss of communication U codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios: A device on the data communication circuit was disconnected while the communication circuit is awake. Power to one or more devices was interrupted during diagnosis. A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold. Battery power was restored to the vehicle and devices on the communication circuit did not all re-initialize at the same time. If a loss of communication U code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
  2. A device may have a U code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U code.
  3. Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.
  4. Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.
  5. Use «Data Link References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__data-link-references) to determine what GMLAN serial data communications the non communicating device uses.
  6. The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify that DTC U0073, U0074, U0075, U0076, U0077, U0078, U2100, P06E4, P1EB9, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not set. If any of the DTCs are set Refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) . If none of the DTCs are set
  3. Refer to Circuit/System Testing.

Note. Use the schematics and connector end views to identify the device's ground, B+, ignition, serial data communication enable, and serial data circuit terminals.

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down. Disconnect the harness connectors at the K17 Electronic Brake Control Module.
  2. Test for less than 10 ohms between each ground circuit terminal and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  3. Ignition ON.
  4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K17 Electronic Brake Control Module. If the test lamp illuminates
  5. Ignition ON.
  6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is OK and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K17 Electronic Brake Control Module. If the test lamp illuminates
  7. Ignition ON.
  8. If equipped, verify a test lamp illuminates between the serial data communication enable circuit terminal and ground. If the test lamp does not illuminate Ignition OFF, disconnect the harness connectors at the K9 Body Control Module. Test for infinite resistance between the serial data communication enable circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the serial data communication enable circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 Body Control Module. If the test lamp illuminates
  9. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down. Disconnect the harness connectors at the device setting the DTC.
  10. Test for less than 2 ohms in each chassis high speed GMLAN serial data circuits end to end between the K17 Electronic Brake Control Module and the device setting the DTC. If 2 ohms or greater Repair the open/high resistance in the serial data circuit. If less than 2 ohms
  11. Replace the K17 Electronic Brake Control Module.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
B+U184A, U0140U184A, U0140
IgnitionU184A, U0140U184A, U0140
Low Speed GMLAN Serial DataU0078*U0078, U184AU0078*
GroundU184A, U0140
* Scan Tool Does Not Communicate With Low Speed GMLAN Device

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device.

The system voltage is between 9-16 V.

A supervised periodic message that includes the transmitter device availability has not been received.

The device is never signaled. Therefore, the specific subsystems will not function.

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.
  1. Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios: A device on the data communication circuit was disconnected while the communication circuit is awake. Power to one or more devices was interrupted during diagnosis. A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold. Battery power was restored to the vehicle and devices on the communication circuit did not all re-initialize at the same time. If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
  2. A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.
  3. Do not replace a device reporting a U-code. The U-code identifies which device needs to be diagnosed for a communication issue.
  4. Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.
  5. Use «Data Link References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__data-link-references) to determine what GMLAN serial data communications the non communicating device uses.
  6. The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify that DTC U0073, U0078, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not set. If any of the DTCs are set Refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) . If none of the DTCs are set
  3. Refer to Circuit/System Testing.

Note. Use the schematics and connector end views to identify the device's ground, B+, ignition, and serial data circuit terminals.

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the K9 Body Control Module. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 10 ohms between each ground circuit terminal and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  3. Ignition ON.
  4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 Body Control Module. If the test lamp illuminates
  5. Ignition ON.
  6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is OK and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 Body Control Module. If the test lamp illuminates
  7. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the device setting the DTC. It may take up to 2 minutes for all vehicle systems to power down.
  8. Test for less than 2 ohms in the low speed GMLAN serial data circuits end to end between the K9 Body Control Module and the device setting the DTC. If 2 ohms or greater Repair the open/high resistance in the serial data circuit. If less than 2 ohms
  9. Replace the K9 Body Control Module.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

Devices on the high speed GMLAN serial data bus and the chassis high speed GMLAN serial data bus must be programmed with software that specifically identifies the correct type and quantity of devices on the bus based on RPO configuration. If a device was not properly configured after installation, the appropriate U Code may be set for that device. No external circuit diagnosis is involved.

  1. Voltage supplied to the device is in the normal operating voltage range.
  2. The vehicle power mode requires serial data communication to occur.
  1. The device is not configured properly.
  2. Control unit recognises a programming error.
  3. CAN-Bus configuration is invalid
  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify DTC U18B9-U18BF is not set. If DTC U18B9-U18BF is set along with other DTCs set Diagnose all other DTCs first. Refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) . If DTC U18B9-U18BF is set without other DTCs set Program the device that set the DTC. Ignition OFF, remove the scan tool, open and close the driver door. Wait 60 s. Verify the DTC does not set. If the DTC sets, replace the appropriate device. If the DTC does not set All OK. If DTC U18B9-U18BF is not set
  3. All OK

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup

  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
MOST ControlU2098 00, U2098 02, U0029 02U0028 00

When the ignition is ON, the A11 Radio initializes the Media Oriented Systems Transport (MOST) bus by sending a short 100 ms low voltage pulse on the electronic control line (or MOST control line) connected to all devices contained on the MOST ring. When MOST receive, transmit, or control line faults are detected, transmit/receive messages will not received as expected from the wakeup request. The A11 Radio and the K74 Human Machine Interface Control Module will then perform diagnostics to isolate these MOST faults. If the MOST control line is shorted low to 0 V for excess amount of time, the A11 Radio will set a U2098 DTC and K74 Human Machine Interface Control Module will set a U0029 02 DTC. At this point the MOST bus will be unable to communicate until the shorted MOST control line is repaired.

  1. The system voltage is between 9-16 V.
  2. The ignition is ON.
  3. The Radio is ON.
  1. The Radio senses a short to ground on the MOST control circuit.
  2. A current DTC is set when a MOST control circuit initialization is invoked and the circuit is detected to be pulled low (0 V) for longer than 1 second.

Many or all entertainment components may not function properly.

The DTC current status is cleared upon a successful MOST control circuit initialization occurs and the circuit is no longer pulled low.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Note. Use the schematics to determine which MOST devices are on the A11 Radio's MOST control circuit 6 X2. Use the connector end views to identify the MOST control circuit terminal for each of those MOST devices.

  1. Ignition OFF, disconnect the harness connectors at an easily accessible MOST device that shares the A11 Radio's MOST control circuit 6 X2. Ignition ON.
  2. Verify that the DTC U2098 or DTC U0029 02 remains current. If the DTC becomes history Replace the MOST device that was just disconnected. If the DTC remains current
  3. With the prior devices disconnected, repeat steps 1 and 2 for each MOST device on the MOST control circuit except the A11 Radio.
  4. Ignition OFF, disconnect the X2 harness connector at the A11 Radio.
  5. Test for infinite resistance between the MOST control circuit terminal 6 X2 at the A11 Radio and ground. If less than infinite resistance Repair the short to ground on the circuit. If infinite resistance
  6. Replace the A11 Radio.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
IgnitionU2099*U0100-U02FFU0100-U02FF
* Vehicle may not start.

The body control module (BCM) activates the ignition circuit, when the ignition key is in ACC, ON or START. The ignition circuit wakes up the devices for serial data bus communication.

  1. The system voltage is between 9-16 V.
  2. The vehicle power mode master requires serial data communication to occur.

The BCM senses a short to ground on the ignition circuit.

  1. The output command is turned off while the malfunction is present.
  2. The devices use a default value for the missing parameters until the next ignition cycle.
  3. The device(s) is never signaled. Therefore, the specific subsystem(s) will not function.
  4. The vehicle will not start while the circuit is shorted to ground.
  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Note. Use the schematic to determine which devices are on the K9 Body Control Module's ignition circuit terminal 23 X4. Use the connector end view to identify the ignition circuit terminal for each of those devices.

  1. Ignition OFF, disconnect the harness connectors at an easily accessible device that shares the K9 Body Control Module's ignition circuit terminal 23 X4. Ignition ON.
  2. Verify that the DTC U2099 remains current. If the DTC becomes history Replace the device that was just disconnected. If the DTC remains current
  3. With the prior devices disconnected, repeat steps 1 and 2 for each device on the ignition circuit except the K9 Body Control Module.
  4. Ignition OFF, disconnect the X4 harness connector at the K9 Body Control Module.
  5. Test for infinite resistance between the ignition circuit terminal 23 X4 at the K9 Body Control Module and ground. If less than infinite resistance Repair the short to ground on the circuit. If infinite resistance
  6. Replace the K9 Body Control Module.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
IgnitionU209EU0100-U02FFU0100-U02FF

The active safety control module activates the object detection ignition circuit, when the ignition is ON. The object detection ignition circuit wakes up the devices for serial data bus communication.

  1. The system voltage is between 9-16 V.
  2. The vehicle power mode master requires serial data communication to occur.

The active safety control module senses a short to ground on the object detection ignition circuit.

The device(s) is never signaled. Therefore, the specific subsystem(s) will not function.

A current DTC clears when the malfunction is no longer present.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Note. Use the schematic to determine which devices are on the K124 active safety control module's ignition circuit 9 X1. Use the connector end view to identify the object detection ignition circuit terminal for each of those devices.

  1. Ignition OFF, disconnect the harness connectors at an easily accessible device that shares the K124 active safety control module's ignition circuit 9 X1. Ignition ON.
  2. Verify that the DTC U209E remains current. If the DTC becomes history Replace the device that was just disconnected. If the DTC remains current
  3. With the prior devices disconnected, repeat steps 1 and 2 for each device on the ignition circuit except the K124 active safety control module.
  4. Ignition OFF, disconnect the X1 harness connector at the K124 active safety control module.
  5. Test for infinite resistance between the ignition circuit terminal 9 X1 at the K124 active safety control module and ground. If less than infinite resistance Repair the short to ground on the circuit. If infinite resistance
  6. Replace the K124 active safety control module.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
IgnitionU209FU0100-U02FFU0100-U02FF

The active safety control module activates the object detection ignition circuit, when the ignition is ON. The object detection ignition circuit wakes up the devices for serial data bus communication.

  1. The system voltage is between 9-16 V.
  2. The vehicle power mode master requires serial data communication to occur.

The active safety control module senses a short to ground on the object detection ignition circuit.

The device(s) is never signaled. Therefore, the specific subsystem(s) will not function.

A current DTC clears when the malfunction is no longer present.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Note. Use the schematic to determine which devices are on the K124 active safety control module's ignition circuit 10 X1. Use the connector end view to identify the object detection ignition circuit terminal for each of those devices.

  1. Ignition OFF, disconnect the harness connectors at an easily accessible device that shares the K124 active safety control module's ignition circuit 10 X1. Ignition ON.
  2. Verify that the DTC U209F remains current. If the DTC becomes history Replace the device that was just disconnected. If the DTC remains current
  3. With the prior devices disconnected, repeat steps 1 and 2 for each device on the ignition circuit except the K124 active safety control module.
  4. Ignition OFF, disconnect the X1 harness connector at the K124 active safety control module.
  5. Test for infinite resistance between the ignition circuit terminal 10 X1 at the K124 active safety control module and ground. If less than infinite resistance Repair the short to ground on the circuit. If infinite resistance
  6. Replace the K124 active safety control module.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

Some devices must be programmed with software that specifically identifies the correct type and quantity of devices on the serial data bus based on RPO configuration. If a device was not properly configured after installation, the appropriate U Code may be set for that device. No external circuit diagnosis is involved.

  1. The system voltage is in the normal operating voltage range.
  2. The vehicle power mode requires serial data communication to occur.
  1. The device is not configured properly.
  2. Control unit recognizes a programming error.
  3. CAN Bus configuration is invalid.
  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the device ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

  1. Ignition ON.
  2. Verify DTC U2101 is not set. If DTC U2101 is set along with other DTCs set Diagnose all other DTCs first. Refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) . If DTC U2101 is set without other DTCs set Program the device that set the DTC. Clear the DTC. Ignition OFF, remove the scan tool, open and close the driver door. Wait 60 s. Verify the DTC does not set. If the DTC sets, replace the appropriate device. If the DTC does not set All OK. If DTC U2101 is not set
  3. All OK

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup

Symptoms - Data Communications

Note. The following steps must be completed before using the symptom tables.

  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) before using the symptom tables in order to verify that all of the following are true: There are no Diagnostic Trouble Codes (DTC) set. The devices can communicate via the serial data links.
  2. Review the system operation in order to familiarize yourself with the system functions. Refer to «Data Link Communications Description and Operation»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__data-link-communications-description-and-operation) .

Visual/Physical Inspection

  1. Inspect for aftermarket devices which could affect the operation of the systems. Refer to «Checking Aftermarket Accessories»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__checking-aftermarket-accessories) .
  2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections .

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

  1. «Scan Tool Does Not Power Up»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Scan Tool Does Not Communicate with High Speed GMLAN Device»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  3. «Scan Tool Does Not Communicate with Low Speed GMLAN Device»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Data Link Connector B+11
Data Link Connector Ground1
1. Scan Tool Does Not Power Up

The data link connector (DLC) is a standardized 16 cavity connector. Connector design and location is dictated by an industry wide standard, and is required to provide the following

  1. Scan tool B+ voltage at terminal 16
  2. Scan tool ground at terminal 4
  3. Common ground at terminal 5
  1. The scan tool will power up with the ignition OFF. Some devices however, will not communicate unless the ignition is ON and the power mode master device sends the appropriate power mode message.
  2. If the B+ circuit, ground circuits, and connections of the data link connector are functioning properly, the malfunction must be due to the scan tool.

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 2 ohms between each of the X84 Data Link Connector ground circuit terminals listed below and ground. Ground circuit terminal 4 Ground circuit terminal 5 If 2 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 2 ohms
  3. Ignition ON.
  4. Verify a test lamp illuminates between the B+ circuit terminal 16 at the X84 Data Link Connector and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If the test lamp illuminates
  5. Refer to the scan tool user guide.
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Chassis High Speed GMLAN Serial Data (+)1U0100-U02FF*1
Chassis High Speed GMLAN Serial Data (-)1U0100-U02FF*1
Ground (DLC, terminal 5)1
* No communications with one or more chassis high speed GMLAN devices. An open in only one chassis high speed GMLAN serial data circuit may allow degraded communication between the devices. An open between the data link connector (DLC) and the first splice/device will only affect the communication with the scan tool. The devices will still communicate. 1. No communication with any chassis high speed GMLAN device.

The chassis high speed GMLAN bus functions the same as the primary high speed GMLAN bus, and the two buses operate in parallel. The chassis high speed GMLAN bus is added to reduce message congestion on the primary high speed bus. Since the chassis high speed GMLAN bus and primary high speed GMLAN bus operate in the same manner, the diagnostics for each are the same.

The serial data is transmitted on two twisted wires that allow speeds up to 500 kbit/s. The twisted pair is terminated with two 120 ohms resistors, one is internal to the electronic brake control module and the other can be a separate resistor in a connector assembly or in another device. The resistors are used as the load for the chassis high speed GMLAN bus during normal vehicle operation. The chassis high speed GMLAN is a differential bus. The chassis high speed GMLAN serial data bus (+) and chassis high speed GMLAN serial data (-) are driven to opposite extremes from a rest or idle level of approximately 2.5 V. Driving the lines to their extremes, adds 1 V to the chassis high speed GMLAN serial data bus (+) circuit and subtracts 1 V from the chassis high speed GMLAN serial data bus (-) circuit. If serial data is lost, devices will set a no communication code against the non-communicating device. Note that a loss of serial data DTC does not represent a failure of the device that set it.

  1. Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of-communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios: A device on the data communication circuit was disconnected while the communication circuit is awake. Power to one or more devices was interrupted during diagnosis. A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold. Battery power was restored to the vehicle and devices on the communication circuit did not all re-initialize at the same time. If a loss-of-communication U code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
  2. Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.
  3. Communication may be available between some devices and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to those devices using multiple serial data communication systems.
  4. An open in the DLC ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle.
  5. Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC).

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify two or more devices are not communicating on the chassis high speed GMLAN serial data circuit. Refer to «Data Link References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__data-link-references) to determine how many devices should be communicating on the bus. If only one device is not communicating Refer to Circuit/System Testing - Testing the Device Circuits. If two or more devices are not communicating
  3. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the scan tool from the X84 Data Link Connector. The following tests will be done at the X84 Data Link Connector. It may take up to 2 minutes for all vehicle systems to power down.
  4. Test for less than 10 ohms between the ground circuit terminal 5 and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  5. Ignition ON.
  6. Test for less than 4.5 V between the serial data circuits listed below and ground. Terminal 12 Terminal 13 If 4.5 V or greater Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Voltage. If less than 4.5 V
  7. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  8. Test for greater than 100 ohms between the serial data circuits listed below and ground. Terminal 12 Terminal 13 If 100 ohms or less Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Ground. If greater than 100 ohms
  9. Test for 50-70 ohms between the serial data circuit terminals 12 and 13. If less than 35 ohms Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short between the Circuits. If between 35-50 ohms There may be a third terminating resistor between the serial data circuits. This can happen if the incorrect device is installed. Some devices are available with and without the terminating resistors installed to reduce the need of terminating resistors in the wiring harness. Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short between the Circuits. If greater than 70 ohms but less than infinite Refer to Circuit/System Testing - Testing the Serial Data Circuits for an Open/High Resistance. If infinite resistance Repair the open/high resistance in the circuit between the X84 Data Link Connector and the first splice/device in the serial data circuit. If between 50-70 ohms
  10. Refer to Circuit/System Testing - Testing the Device Circuits.

Note. Each device may need to be disconnected to isolate a circuit fault. Use the schematic to identify the following: Chassis high speed GMLAN devices the vehicle is equipped with Chassis high speed GMLAN serial data circuit terminating resistors Device locations on the chassis high speed GMLAN serial data circuits Each device's ground, B+, ignition, and chassis high speed GMLAN serial data circuit terminals Some devices with an internal terminating resistor have a loop in the harness that connects the internal terminating resistor to the serial data circuit. When wired this way, test these loop circuits for the appropriate failure mode short to voltage, short to ground, or open/high resistance prior to replacing the device for each of the following tests.

Testing the Serial Data Circuits for a Short to Voltage

  1. Ignition OFF, disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at an easily accessible device, ignition ON.
  2. Test for greater than 4.5 V between each serial data circuit at the device connector that was just disconnected and ground. If each serial data circuit is 4.5 V or less Ignition OFF. Test for less than 10 ohms between each of the device's ground circuit terminals and ground. If 10 ohms or greater, repair the open/high resistance in the circuit. If less than 10 ohms, replace the device that was disconnected. If any serial data circuit is greater than 4.5 V
  3. Ignition OFF, disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted to voltage, ignition ON.
  4. Test for greater than 4.5 V between each serial data circuit at the device connector that was just disconnected and ground. If each serial data circuit is 4.5 V or less Ignition OFF. Test for less than 10 ohms between each of the device's ground circuit terminals and ground. If 10 ohms or greater, repair the open/high resistance in the circuit. If less than 10 ohms, replace the device that was disconnected. If any serial data circuit is greater than 4.5 V
  5. Repeat step 3 until one of the following conditions are isolated: A short to voltage on the serial data circuit between two devices or splice packs, if equipped. A short to voltage on the serial data circuit between a device and a terminating resistor.

Testing the Serial Data Circuits for a Short to Ground

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at an easily accessible device.
  3. Test for greater than 100 ohms between each serial data circuit at the device connector that was just disconnected and ground. If each serial data circuit is 100 ohms or greater Replace the device that was disconnected. If any serial data circuit is less than 100 ohms
  4. Disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted to ground.
  5. Test for greater than 100 ohms between each serial data circuit at the device connector that was just disconnected and ground. If both serial data circuits are 100 ohms or greater Replace the device that was disconnected. If any serial data circuit is less than 100 ohms
  6. Repeat step 4 until one of the following conditions are isolated: A short to ground on the serial data circuit between two devices or splice packs, if equipped. A short to ground on the serial data circuit between a device and a terminating resistor. A short to ground on the serial data circuit between the X84 Data Link Connector and the first device or splice pack.

Testing the Serial Data Circuits for a Short between the Circuits

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at an easily accessible device that is not communicating.
  3. Test for greater than 110 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 110 ohms or greater Replace the device that was disconnected. If any pair of serial data circuits is less than 110 ohms
  4. Connect the harness connectors at the device that was disconnected.
  5. Disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted together.
  6. Test for greater than 110 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 110 ohms or greater Replace the device that was disconnected. If any pair of serial data circuits is less than 110 ohms
  7. Repeat step 4 until one of the following conditions are isolated: Serial data circuits shorted together between two devices or splice packs, if equipped. Serial data circuits shorted together between a device and a terminating resistor. Serial data circuits shorted together between the X84 Data Link Connector and the first device or splice pack. A shorted terminating resistor.

Testing the Serial Data Circuits for an Open/High Resistance

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at an easily accessible device that is not communicating.
  3. Test for less than 130 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuit is 130 ohms or less Replace the device that was disconnected. If any pair of serial data circuits is greater than 130 ohms
  4. Connect the harness connectors at the device that was disconnected.
  5. Disconnect the harness connectors with the chassis high speed GMLAN serial data circuits at another device, in the direction of the circuit with the open/high resistance.
  6. Test for less than 130 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 130 ohms or less Replace the device that was disconnected. If any pair of serial data circuits is greater than 130 ohms
  7. Repeat step 4 until one of the following conditions are isolated: An open/high resistance on the serial data circuit between two devices or splice packs, if equipped. An open/high resistance on the serial data circuit between a device and a terminating resistor. An open/high resistance terminating resistor.

Testing the Device Circuits

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors at an easily accessible device that is not communicating.
  3. Test for less than 10 ohms between each ground circuit terminal and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the disconnected device. If the test lamp illuminates
  5. Ignition ON.
  6. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which has a fuse in the circuit, and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is OK and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the disconnected device. If the test lamp illuminates
  7. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which is controlled by a control module, and ground. If the test lamp does not illuminate Ignition OFF, disconnect the harness connectors at the control module that controls the ignition circuit. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the control module that controls the ignition circuit. If the test lamp illuminates
  8. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  9. Test for less than 130 ohms between each pair of chassis high speed GMLAN serial data circuits at the device connector that was just disconnected. If any pair of serial data circuits is greater than 130 ohms Repair the open/high resistance in the serial data circuits between the disconnected device and the circuit splice in the serial data circuits. If each pair of serial data circuits is 130 ohms or less
  10. Replace the device that was disconnected.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
High Speed GMLAN Serial Data (+)1U0100-U02FF*1
High Speed GMLAN Serial Data (-)1U0100-U02FF*1
Ground (DLC, terminal 5)1
* No communications with one or more high speed GMLAN devices. An open in only one high speed GMLAN serial data circuit may allow degraded communication between the devices. An open between the data link connector (DLC) and the first splice/device will only affect the communication with the scan tool. The devices will still communicate. 1. No communication with any high speed GMLAN device

The serial data is transmitted on two twisted wires that allow speeds up to 500 Kb/s. The twisted pair is terminated with two 120 ohms resistors, one is internal to the engine control module (ECM) and the other can be a separate resistor in a connector assembly or in another device. The resistors are used as the load for the High Speed GMLAN bus during normal vehicle operation. The high speed GMLAN is a differential bus. The high speed GMLAN serial data bus (+) and high speed GMLAN serial data (-) are driven to opposite extremes from a rest or idle level of approximately 2.5 V. Driving the lines to their extremes, adds 1 V to the high speed GMLAN serial data bus (+) circuit and subtracts 1 V from the high speed GMLAN serial data bus (-) circuit. If serial data is lost, devices will set a no communication code against the non-communicating device. Note that a loss of serial data DTC does not represent a failure of the device that set it.

  1. Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of-communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios: A device on the data communication circuit was disconnected while the communication circuit is awake. Power to one or more devices was interrupted during diagnosis. A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold. Battery power was restored to the vehicle and devices on the communication circuit did not all re-initialize at the same time. If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
  2. Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.
  3. Communication may be available between some devices and the scan tool with the high speed GMLAN serial data system inoperative. This condition is due to those devices using multiple serial data communication systems.
  4. An open in the DLC ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle.
  5. The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus.
  6. Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC) and no low speed GMLAN communications with the scan tool.
  7. These conditions may be caused by the installation of an aftermarket navigation radio module (see bulletins). Some customers may comment of one or more of the following concerns: Vehicle will not crank Vehicle cranks but will not start Vehicle stability enhancement system warning lights and messages PRNDL gear indicator position errors

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify two or more devices are not communicating on the high speed GMLAN serial data circuit. Refer to «Data Link References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__data-link-references) to determine how many devices should be communicating on the bus. If only one device is not communicating Refer to Circuit/System Testing - Testing the Device Circuits. If two or more devices are not communicating
  3. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the scan tool from the X84 data link connector. The following tests will be done at the X84 data link connector. It may take up to 2 minutes for all vehicle systems to power down.
  4. Test for less than 10 ohms between the ground circuit terminal 5 and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  5. Ignition ON.
  6. Test for less than 4.5 V between the serial data circuits listed below and ground. Terminal 6 Terminal 14 If 4.5 V or greater Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Voltage. If less than 4.5 V
  7. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  8. Test for greater than 100 ohms between the serial data circuits listed below and ground. Terminal 6 Terminal 14 If 100 ohms or less Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Ground. If greater than 100 ohms
  9. Test for 50-70 ohms between the serial data circuit terminals 6 and 14. If less than 35 ohms Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short between the Circuits. If between 35-50 ohms There may be a third terminating resistor between the serial data circuits. This can happen if the incorrect device is installed. Some devices are available with and without the terminating resistors installed to reduce the need of terminating resistors in the wiring harness. Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short between the Circuits. If greater than 70 ohms but less than infinite Refer to Circuit/System Testing - Testing the Serial Data Circuits for an Open/High Resistance. If infinite resistance Repair the open/high resistance in the circuit between the X84 data link connector and the first splice/device in the serial data circuit. If between 50-70 ohms
  10. Refer to Circuit/System Testing - Testing the Device Circuits.

Note. Each device may need to be disconnected to isolate a circuit fault. Use the schematic to identify the following: High speed GMLAN devices the vehicle is equipped with High speed GMLAN serial data circuit terminating resistors Device locations on the high speed GMLAN serial data circuits Each device's ground, B+, ignition, and high speed GMLAN serial data circuit terminals Some devices with an internal terminating resistor have a loop in the harness that connects the internal terminating resistor to the serial data circuit. When wired this way, test these loop circuits for the appropriate failure mode short to voltage, short to ground, or open/high resistance prior to replacing the device for each of the following tests.

Testing the Serial Data Circuits for a Short to Voltage

  1. Ignition OFF, disconnect the harness connectors with the high speed GMLAN serial data circuits at an easily accessible device, ignition ON.
  2. Test for greater than 4.5 V between each serial data circuit at the device connector that was just disconnected and ground. If each serial data circuit is 4.5 V or less Ignition OFF. Test for less than 10 ohms between each of the device's ground circuit terminals and ground. If 10 ohms or greater, repair the open/high resistance in the circuit. If less than 10 ohms, replace the device that was disconnected. If any serial data circuit is greater than 4.5 V
  3. Ignition OFF, disconnect the harness connectors with the high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted to voltage, ignition ON.
  4. Test for greater than 4.5 V between each serial data circuit at the device connector that was just disconnected and ground. If each serial data circuit is 4.5 V or less Ignition OFF. Test for less than 10 ohms between each of the device's ground circuit terminals and ground. If 10 ohms or greater, repair the open/high resistance in the circuit. If less than 10 ohms, replace the device that was disconnected. If any serial data circuit is greater than 4.5 V
  5. Repeat step 3 until one of the following conditions are isolated: A short to voltage on the serial data circuit between two devices or splice packs, if equipped. A short to voltage on the serial data circuit between a device and a terminating resistor.

Testing the Serial Data Circuits for a Short to Ground

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors with the high speed GMLAN serial data circuits at an easily accessible device.
  3. Test for greater than 100 ohms between each serial data circuit at the device connector that was just disconnected and ground. If each serial data circuit is 100 ohms or greater Replace the device that was disconnected. If any serial data circuit is less than 100 ohms
  4. Disconnect the harness connectors with the high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted to ground.
  5. Test for greater than 100 ohms between each serial data circuit at the device connector that was just disconnected and ground. If both serial data circuits are 100 ohms or greater Replace the device that was disconnected. If any serial data circuit is less than 100 ohms
  6. Repeat step 4 until one of the following conditions are isolated: A short to ground on the serial data circuit between two devices or splice packs, if equipped. A short to ground on the serial data circuit between a device and a terminating resistor. A short to ground on the serial data circuit between the X84 data link connector and the first device or splice pack.

Testing the Serial Data Circuits for a Short between the Circuits

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors with the high speed GMLAN serial data circuits at an easily accessible device that is not communicating.
  3. Test for greater than 110 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 110 ohms or greater Replace the device that was disconnected. If any pair of serial data circuits is less than 110 ohms
  4. Connect the harness connectors at the device that was disconnected.
  5. Disconnect the harness connectors with the high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted together.
  6. Test for greater than 110 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 110 ohms or greater Replace the device that was disconnected. If any pair of serial data circuits is less than 110 ohms
  7. Repeat step 4 until one of the following conditions are isolated: Serial data circuits shorted together between two devices or splice packs, if equipped. Serial data circuits shorted together between a device and a terminating resistor. Serial data circuits shorted together between the X84 data link connector and the first device or splice pack. A shorted terminating resistor.

Testing the Serial Data Circuits for an Open/High Resistance

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors with the high speed GMLAN serial data circuits at an easily accessible device that is not communicating.
  3. Test for less than 130 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 130 ohms or less Replace the device that was disconnected. If any pair of serial data circuits is greater than 130 ohms
  4. Connect the harness connectors at the device that was disconnected.
  5. Disconnect the harness connectors with the high speed GMLAN serial data circuits at another device, in the direction of the circuit with the open/high resistance.
  6. Test for less than 130 ohms between each pair of serial data circuits at the device connector that was just disconnected. If each pair of serial data circuits is 130 ohms or less Replace the device that was disconnected. If any pair of serial data circuits is greater than 130 ohms
  7. Repeat step 4 until one of the following conditions are isolated: An open/high resistance on the serial data circuit between two devices or splice packs, if equipped. An open/high resistance on the serial data circuit between a device and a terminating resistor. An open/high resistance terminating resistor.

Testing the Device Circuits

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  2. Disconnect the harness connectors at an easily accessible device that is not communicating.
  3. Test for less than 10 ohms between each ground circuit terminal and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the disconnected device. If the test lamp illuminates
  5. Ignition ON.
  6. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which has a fuse in the circuit, and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is OK and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the disconnected device. If the test lamp illuminates
  7. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which is controlled by a control module, and ground. If the test lamp does not illuminate Ignition OFF, disconnect the harness connectors at the control module that controls the ignition circuit. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the control module that controls the ignition circuit. If the test lamp illuminates
  8. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  9. Test for less than 130 ohms between each pair of high speed GMLAN serial data circuits at the device connector that was just disconnected. If any pair of serial data circuits is greater than 130 ohms Repair the open/high resistance in the serial data circuits between the disconnected device and the circuit splice in the serial data circuits. If each pair of serial data circuits is 130 ohms or less
  10. Replace the device that was disconnected.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/cadillac/ats/i-2012-2014/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Low Speed GMLAN Serial Data1U0100-U02FF*1
Ground (DLC, terminal 5)1*
* An open between the X84 Data Link Connector (DLC) and the first splice pack/device will only affect the communication with the scan tool. 1. No communication with any low speed GMLAN device

The serial data is transmitted over a single wire to the appropriate devices. The transmission speed for GMLAN low speed is up to 83.33 kbit/s. Under normal vehicle operating conditions, the speed of the bus is 33.33 kbit/s. The devices toggle the serial data circuit between 0-5 V during normal communications. To wake the devices connected to the low speed GMLAN serial data circuit, a voltage wake up pulse of 10 V is sent out. If serial data is lost, devices will set a no communication code against the non-communicating device. A loss of serial data communications DTC does not represent a failure of the device that set it.

  1. Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U code present. However, there is no associated "current" or "active" status. Loss of communication U codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios: A device on the data communication circuit was disconnected while the communication circuit is awake. Power to one or more devices was interrupted during diagnosis A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold. Battery power was restored to the vehicle and devices on the communication circuit did not all re-initialize at the same time. If a loss of communication U- code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
  2. Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.
  3. Communication may be available between the device and the scan tool with the low speed GMLAN serial data system inoperative. This condition is due to the device using both the high and low speed GMLAN systems.
  4. An open in the low speed GMLAN serial data circuit between the splice pack and a device will only affect that specific device. This type of failure will set a loss of communication DTC for each device affected, and the other devices will still communicate.
  5. An open in the X84 Data Link Connector (DLC) ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle.
  6. The engine may not start when there is a total malfunction of the low speed GMLAN serial data circuit.
  7. Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC) and no low speed LAN communications with the scan tool.
  8. These conditions may be caused by the installation of an aftermarket navigation radio device (see bulletins). Some customers may comment of one or more of the following concerns: Vehicle will not crank Vehicle cranks but will not start Vehicle stability enhancement system warning lights and messages PRNDL gear indicator position errors

Schematic Reference

  1. «Data Communication Schematics»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Note. Use the schematic to identify the following: Devices the vehicle is equipped with Device and splice pack locations on the low speed GMLAN serial data circuit The low speed GMLAN serial data circuit terminals for each device or splice pack

  1. Attempt to communicate with all devices on the low speed GMLAN serial data circuit. Refer to «Data Link References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system__data-link-references) .
  2. Verify which devices are communicating on the low speed GMLAN serial data circuit. If only one device is not communicating Diagnose that device only. Refer to «DTC U0100-U02FF»(/cadillac/ats/i-2012-2014/remont/communication-devices/#data-communication-system) . If one or more devices are communicating but not all Refer to Circuit/System Testing - Testing the Serial Data Circuit for an Open/High Resistance. If none of the devices are communicating
  3. Ignition OFF, all access doors closed, all vehicle systems OFF, all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the scan tool from the X84 Data Link Connector. The following tests will be done at the X84 Data Link Connector. It may take up to 2 minutes for all vehicle systems to power down.
  4. Test for less than 10 ohms between the ground circuit terminal 5 and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  5. Ignition ON.
  6. Test for less than 4.5 V between the serial data circuit terminal 1 and ground. If 4.5 V or greater Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Voltage. If less than 4.5 V
  7. Ignition OFF, all access doors closed, all vehicle systems OFF, all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  8. Test for greater than 100 ohms between the serial data circuit terminal 1 and ground. If 100 ohms or less Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Ground. If greater than 100 ohms
  9. Disconnect the appropriate harness connector at the first splice pack closest in the circuit to the X84 Data Link Connector.
  10. Test for less than 2 ohms between the X84 Data Link Connector's serial data circuit terminal 1 and the splice pack harness connector's serial data input terminal. If 2 ohms or greater Repair the open/high resistance in the serial data circuit. If less than 2 ohms
  11. Replace the splice pack.

Testing the Serial Data Circuits for a Short to Voltage

  1. Ignition OFF, disconnect the appropriate harness connectors at all low speed GMLAN serial data splice packs, ignition ON.
  2. Test for less than 4.5 V between the serial data circuit terminal 1 at the X84 Data Link Connector and ground. If 4.5 V or greater Repair the short to voltage on the serial data circuit. If less than 4.5 V
  3. Test for less than 4.5 V between each low speed GMLAN serial data circuit at a splice pack and ground. If any serial data circuit is greater than 4.5 V Ignition OFF, disconnect all devices on the failed serial data circuit, ignition ON. Test for less than 1 V between each section of the failed serial data circuit and ground. If 1 V or greater, repair the short to voltage in the circuit. If less than 1 V Connect the splice pack and connect the first device on the failed serial data circuit, ignition ON. Verify the scan tool communicates or not with the low speed GMLAN serial data circuit. If the scan tool does not communicate, replace the device that was just connected. If the scan tool communicates and there are more devices to connect, connect the next device and repeat step 3.4. If the scan tool communicates and there are no more devices to connect All OK. If all serial data circuits are less than 4.5 V
  4. All OK.

Testing the Serial Data Circuits for a Short to Ground

  1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the appropriate harness connectors at all low speed GMLAN serial data splice packs.
  2. Test for infinite resistance between the serial data circuit terminal 1 at the X84 Data Link Connector and ground. If less than infinite resistance Repair the short to ground on the serial data circuit. If infinite resistance
  3. Test for greater than 100 ohms between each low speed GMLAN serial data circuit at a splice pack and ground. If any serial data circuit is 100 ohms or less Disconnect all devices on the failed serial data circuit. Test for infinite resistance between each section of the failed serial data circuit and ground. If less than infinite resistance, repair the short to ground in the circuit. If infinite resistance Connect the splice pack and connect the first device on the failed serial data circuit, ignition ON. Verify the scan tool communicates or not with the low speed GMLAN serial data circuit. If the scan tool does not communicate, replace the device that was just connected. If the scan tool communicates and there are more devices to connect, connect the next device and repeat step 3.4. If the scan tool communicates and there are no more devices to connect All OK. If all serial data circuits are greater than 100 ohms
  4. All OK.

Testing the Serial Data Circuit for an Open/High Resistance

  1. Ignition OFF and all vehicle systems OFF, disconnect the splice pack containing the devices that are not communicating on the low speed GMLAN serial data circuit.
  2. Test for less than 2 ohms between the X84 Data Link Connector terminal 1 and the disconnected splice pack. If 2 ohms or greater Repair the open/high resistance in the serial data circuit. If less than 2 ohms
  3. Disconnect all devices on the failed serial data circuit.
  4. Test for less than 2 ohms between each section of the failed serial data circuit end to end. If 2 ohms or greater Repair the open/high resistance in the serial data circuit. If less than 2 ohms
  5. Connect the splice pack and connect the first device on the failed serial data circuit.
  6. Verify if the device communicates or not with the scan tool. If the device does not communicates Replace the device. If the device communicates and there are more devices to connect Connect the next device on the failed serial data circuit and repeat step 6. If all devices are connected and communicating
  7. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs»(/cadillac/ats/i-2012-2014/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__gmlan-and-media-oriented-systems-transport)
  2. «Control Module References»(/cadillac/ats/i-2012-2014/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for device replacement, programming and setup

Data Link References

This table identifies which serial data link that a particular device uses for in-vehicle data transmission. Some devices may use more than one data link to communicate. Some devices may have multiple communication circuits passing through them without actively communicating on that data link. This table is used to assist in correcting a communication malfunction. Not all devices listed will be applicable to all vehicles. Refer to the schematics to determine which devices apply. For the description and operation of these serial data communication circuits, refer to Data Link Communications Description and Operation .

Reference Information

Schematic Reference: Data Communication Schematics

CodeDeviceData Link TypeDiagnostic Procedure
A11RadioLow Speed GMLAN MOST BusScan Tool Does Not Communicate with Low Speed GMLAN Device DTC U0028
A20Radio/HVAC ControlsLocal Interconnect Network (LIN)DTC U1500-U15FF
A33Media Disc PlayerMOST BusDTC U0028
B67Ultrasonic Intrusion SensorLocal Interconnect Network (LIN)DTC U1500-U15FF
B99Steering Wheel Angle SensorChassis High Speed GMLANScan Tool Does Not Communicate with Chassis High Speed GMLAN Device
B117Rain SensorLocal Interconnect Network (LIN)DTC U1500-U15FF
B119Multi-axis Acceleration SensorChassis High Speed GMLANScan Tool Does Not Communicate with Chassis High Speed GMLAN Device
B174Frontview CameraLow Speed GMLANScan Tool Does Not Communicate with Low Speed GMLAN Device
B218LSide Object Sensor Module - LeftLow Speed GMLANScan Tool Does Not Communicate with Low Speed GMLAN Device
B218RSide Object Sensor Module - RightLow Speed GMLANScan Tool Does Not Communicate with Low Speed GMLAN Device
B233BRadar Sensor Module - Long RangeObject BusDTC U0075
B233LFRadar Sensor Module - Short Range Left FrontObject BusDTC U0075
B233RFRadar Sensor Module - Short Range Right FrontObject BusDTC U0075
B233RRadar Sensor Module - Short Range RearObject BusDTC U0075
E13LHeadlamp - LeftLocal Interconnect Network (LIN)DTC U1500-U15FF
E13RHeadlamp - RightLocal Interconnect Network (LIN)DTC U1500-U15FF
K9Body Control ModuleHigh Speed GMLAN Low Speed GMLAN Local Interconnect Network (LIN)Scan Tool Does Not Communicate with High Speed GMLAN Device Scan Tool Does Not Communicate with Low Speed GMLAN Device DTC U1500-U15FF
K17Electronic Brake Control ModuleHigh Speed GMLAN Chassis High Speed GMLANScan Tool Does Not Communicate with High Speed GMLAN Device Scan Tool Does Not Communicate with Chassis High Speed GMLAN Device
K19Suspension Control ModuleHigh Speed GMLAN Chassis High Speed GMLANScan Tool Does Not Communicate with High Speed GMLAN Device Scan Tool Does Not Communicate with Chassis High Speed GMLAN Device
K20Engine Control ModuleHigh Speed GMLANScan Tool Does Not Communicate with High Speed GMLAN Device
K26Headlamp Control ModuleHigh Speed GMLAN Local Interconnect Network (LIN)Scan Tool Does Not Communicate with High Speed GMLAN Device DTC U1500-U15FF
K29Seat Heating Control ModuleLocal Interconnect Network (LIN)DTC U1500-U15FF
K33HVAC Control ModuleLow Speed GMLAN Local Interconnect Network (LIN)Scan Tool Does Not Communicate with Low Speed GMLAN Device DTC U1500-U15FF
K33AHVAC Control Module - AuxiliaryLocal Interconnect Network (LIN)DTC U1500-U15FF
K36Inflatable Restraint Sensing and Diagnostic ModuleChassis High Speed GMLAN (without UGN) Low Speed GMLANScan Tool Does Not Communicate with Chassis High Speed GMLAN Device Scan Tool Does Not Communicate with Low Speed GMLAN Device
K38Chassis Control ModuleHigh Speed GMLANScan Tool Does Not Communicate with High Speed GMLAN Device
K40DSeat Memory Control Module - DriverLow Speed GMLAN Local Interconnect Network (LIN)Scan Tool Does Not Communicate with Low Speed GMLAN Device DTC U1500-U15FF
K41Front and Rear Parking Assist Control ModuleLow Speed GMLANScan Tool Does Not Communicate with Low Speed GMLAN Device
K42Pedestrian Impact Detection Control ModuleHigh Speed GMLANScan Tool Does Not Communicate with High Speed GMLAN Device
K43Power Steering Control ModuleHigh Speed GMALN Chassis High Speed GMALNScan Tool Does Not Communicate with High Speed GMLAN Device Scan Tool Does Not Communicate with Chassis High Speed GMLAN Device
K47Rear Differential Clutch Control ModuleHigh Speed GMALN Chassis High Speed GMALNScan Tool Does Not Communicate with High Speed GMLAN Device Scan Tool Does Not Communicate with Chassis High Speed GMLAN Device
K60Steering Column Lock ModuleLow Speed GMLANScan Tool Does Not Communicate with Low Speed GMLAN Device
K69Transfer Case Control ModuleHigh Speed GMLANScan Tool Does Not Communicate with High Speed GMLAN Device
K71 / Q8Transmission Control Module / Control Solenoid Valve AssemblyHigh Speed GMLANScan Tool Does Not Communicate with High Speed GMLAN Device
K73Telematics Communication Interface Control ModuleHigh Speed GMALN Low Speed GMLANScan Tool Does Not Communicate with High Speed GMLAN Device Scan Tool Does Not Communicate with Low Speed GMLAN Device
K74Human Machine Interface Control ModuleHigh Speed GMALN MOST BusScan Tool Does Not Communicate with High Speed GMLAN Device DTC U0028
K76Steering Column Control ModuleLocal Interconnect Network (LIN)DTC U1500-U15FF
K83Parking Brake Control ModuleHigh Speed GMLANScan Tool Does Not Communicate with High Speed GMLAN Device
K84Keyless Entry Control ModuleLow Speed GMLANScan Tool Does Not Communicate with Low Speed GMLAN Device
K85Passenger Presence ModuleLow Speed GMLANScan Tool Does Not Communicate with Low Speed GMLAN Device
K89Immobilizer Control ModuleLocal Interconnect Network (LIN)DTC U1500-U15FF
K91Battery Saver ModuleLocal Interconnect Network (LIN)DTC U1500-U15FF
K96LMirror Control Module - LeftLocal Interconnect Network (LIN)DTC U1500-U15FF
K101Trailer Interface Control ModuleLow Speed GMLANScan Tool Does Not Communicate with Low Speed GMLAN Device
K109Frontview Camera ModuleObject BusDTC U0075
K124Active Safety Control ModuleHigh Speed GMLAN Chassis High Speed GMLAN Object Bus Low Speed GMLANScan Tool Does Not Communicate with High Speed GMLAN Device Scan Tool Does Not Communicate with Chassis High Speed GMLAN Device DTC U0075 Scan Tool Does Not Communicate with Low Speed GMLAN Device
M69Sunroof MotorLocal Interconnect Network (LIN)DTC U1500-U15FF
M74DWindow Motor - DriverLocal Interconnect Network (LIN)DTC U1500-U15FF
M74PWindow Motor - PassengerLocal Interconnect Network (LIN)DTC U1500-U15FF
P2Transmission Shift Lever Position IndicatorLocal Interconnect Network (LIN)DTC U1500-U15FF
P16Instrument ClusterLow Speed GMLAN MOST Bus Local Interconnect Network (LIN)Scan Tool Does Not Communicate with Low Speed GMLAN Device DTC U0028 DTC U1500-U15FF
P17Info Display ModuleLow Speed GMLAN Local Interconnect Network (LIN)Scan Tool Does Not Communicate with Low Speed GMLAN Device DTC U1500-U15FF
P25Power Sounder Content Theft Deterrent Alarm ModuleLocal Interconnect Network (LIN)DTC U1500-U15FF
P29Head-Up DisplayLocal Interconnect Network (LIN)DTC U1500-U15FF
S70RSteering Wheel Controls Switch - RightLocal Interconnect Network (LIN)DTC U1500-U15FF
S79DWindow Switch - DriverLocal Interconnect Network (LIN)DTC U1500-U15FF
S79LRWindow Switch - Left RearLocal Interconnect Network (LIN)DTC U1500-U15FF
S79PWindow Switch - PassengerLocal Interconnect Network (LIN)DTC U1500-U15FF
S79RRWindow Switch - Right RearLocal Interconnect Network (LIN)DTC U1500-U15FF
T3Audio AmplifierLow Speed GMLAN MOST BusScan Tool Does Not Communicate with Low Speed GMLAN Device DTC U0028

Data Link References

Scheme 17

Scheme 17: Body Control Module Replacement
Scheme 17: Body Control Module Replacement
CalloutComponent Name
Preliminary Procedure Remove the instrument panel lower trim panel insulator - right side. Refer to Instrument Panel Lower Trim Panel Insulator Replacement (Left Side) , Instrument Panel Lower Trim Panel Insulator Replacement (Right Side) .
1Body Control Module Procedure Disconnect the electrical connectors. Push tabs to release the body control module from the bracket. Reprogram the module if replaced. Refer to Control Module References .

Body Control Module Replacement

Body Control System Description and Operation

The body control system consists of the body control module (BCM), communications, and various input and outputs. Some inputs, outputs and messages require other modules to interact with the BCM. The BCM also has discrete input and output terminals to control the vehicle's body functions. The BCM is wired to the high speed GMLAN serial data bus, low speed GMLAN serial data bus and Multiple LIN buses and acts as a gateway between them.

Power Mode Master

This vehicle body control module (BCM) functions as the power mode master (PMM). The ignition switch is a low current switch with multiple discrete ignition switch signals to the PMM for determining the power mode that will be sent over the serial data circuits to the other modules that need this information; the PMM will activate relays and other direct outputs of the PMM as needed. Refer to Power Mode Description and Operation for a complete description of power mode functions.

Gateway

The body control module (BCM) in this vehicle functions as a gateway or translator. The purpose of the gateway is to translate serial data messages between the GMLAN high speed bus and the GMLAN low speed bus for communication between the various modules. The gateway will interact with each network according to that network's transmission protocol.

All communication between the BCM and a scan tool is on the high speed GMLAN serial data circuits. A lost communication DTC typically is set in modules other than the module with a communication failure.

Body Control

The various body control module (BCM) input and output circuits are illustrated in the corresponding functional areas on the BCM electrical schematics. Refer to the Body Control System Schematics for more detailed information.

Data Link Communications Description and Operation

Note. This is an overview of different serial data buses used by GM devices to communicate with each others. Use Data Communication Schematics to find out which serial data buses are configured for a specific vehicle.

There are many components in a vehicle that rely on information from other sources, transmit information to other sources, or both. Serial data communication networks provide a reliable, cost effective, way for various components of the vehicle to "talk" to one another and share information.

GM uses a number of different communication buses to insure the timely and efficient exchange of information between devices. When compared to each other, some of these buses are different in nature as far as speed, signal characteristics, and behavior. An example of this is the High Speed GMLAN and Low Speed GMLAN buses.

On the other hand, when other buses are compared to each other they have similar characteristics and simply operate in parallel. In this case they are used to group together components which have high interaction. Examples are the High Speed GMLAN, Powertrain Expansion, and Chassis Expansion buses. This allows them to communicate with each other on a bus with reduced message congestion insuring faster and the more timely exchange of information than if all vehicle devices were on a single bus.

The majority of information that exists within a given network generally stays local; however some information will have to be shared on other networks. Control modules designated as Gateway's perform the function of transferring information between the various buses. A Gateway module is connected to at least 2 buses and will interact with each network according to its message strategy and transmission models.

GMLAN provides the capability for a receiving device to monitor message transmissions from other devices in order to determine if messages of interest are not being received. The primary purpose is to allow reasonable default values to be substituted for the information no longer being received. Additionally, a device may set a Diagnostic Trouble Code to indicate that the device it is expecting information from is no longer communicating.

High Speed GMLAN Circuit Description

A High Speed GMLAN Bus is used where data needs to be exchanged at a high enough rate to minimize the delay between the occurrence of a change in sensor value and the reception of this information by a control device using the information to adjust vehicle system performance.

The High Speed GMLAN serial data network consists of two twisted wires. One signal circuit is identified as GMLAN-High and the other signal circuit is identified as GMLAN-Low. At each end of the data bus there is a 120 ohms termination resistor between the GMLAN-High and GMLAN-Low circuits.

Data symbols (1's and 0's) are transmitted sequentially at a rate of 500 Kbit/s. The data to be transmitted over the bus is represented by the voltage difference between the GMLAN-High signal voltage and the GMLAN-Low signal voltage.

When the two wire bus is at rest the GMLAN-High and GMLAN-Low signal circuits are not being driven and this represents a logic "1". In this state both signal circuits are at the same voltage of 2.5 V. The differential voltage is approximately 0 V.

When a logic "0" is to be transmitted, the GMLAN-High signal circuit is driven higher to about 3.5 V and the GMLAN-Low circuit is driven lower to about 1.5 V. The differential voltage becomes approximately 2.0 (+/- 0.5) V.

Chassis High Speed GMLAN Circuit Description

The GMLAN Chassis Expansion Bus is basically a copy of the High Speed GMLAN Bus except that its use is reserved for chassis components. This implementation splits message congestion between two parallel buses helping to insure timely message transmission and reception. Sometimes communication is required between the Chassis Expansion Bus and the primary High Speed GMLAN Bus. This is accomplished by using the K17 Electronic Brake Control Module (EBCM) as the Gateway module. Since the High Speed GMLAN Chassis Expansion Bus and primary High Speed GMLAN Bus operate in the same manner, the diagnostics for each are similar.

Object High Speed GMLAN Circuit Description

The GMLAN Object Bus is basically a copy of the High Speed GMLAN Bus except that its use is reserved for the enhanced safety system. This implementation is used to isolate the heavy communication among the enhanced safety system devices from the other vehicle buses, reducing congestion. The K124 Active Safety Control Module is connected to the Object Bus as well as the Primary High Speed GMLAN Bus, the Chassis Expansion Bus, and the Low Speed GMLAN Bus. The K124 Active Safety Control Module acts as a Gateway module for all required communication between the Object Bus devices and devices on these other vehicle buses. The GMLAN Object Bus operates in the same manner as the Chassis Expansion and Primary High Speed buses and so the diagnostics are similar. The Object Bus is physically partitioned into a Front Object Bus and a Rear Object Bus with each partition having its own communication enable circuit to activate the partition, but functional operation of both is identical. The Front Object Bus standard devices are the K124 Active Safety Control Module, the K109 Frontview Camera Module, and the B233B Radar Sensor Module - Long Range. The Front Object Bus optional devices are the B233LF Radar Sensor Module - Short Range Left Front and the B233RF Radar Sensor Module - Short Range Right Front. The Rear Object Bus is optional and when present will have the K124 Active Safety Control Module and B233R Radar Sensor Module - Short Range Rear on the bus, and optionally the Radar Sensor Module - Short Range Right Rear. All Object Bus components are powered by the K124 Active Safety Control Module via the communication enable circuits, except the K109 Frontview Camera Module which is powered directly by battery.

Media Oriented Systems Transport (MOST) Circuit Description

The MOST Infotainment network is a dedicated high speed multimedia streaming data bus independent from GMLAN. The MOST bus will be configured in a physical hardwired loop with each device within the bus sends and receives data on an assigned MOST addresses in a set order. Each device on the MOST bus will be required to have twisted pair copper wires (2 transmit TX, 2 receive RX, and 1 electronic control line which is a 12 V wakeup signal line). The A11 Radio is the MOST Master and will monitor the bus for vehicle configuration, Infotainment data messages and errors on the bus. The MOST initialization consists of a short 100 ms low voltage pulse on the electronic control line (or MOST control line) connected to all devices contained on the MOST ring. This wakeup message once received by each device, will first respond with a generic device response. Once these initial responses on the MOST bus are reported successfully without error to the A11 Radio, the second data request will record the MOST device addresses, their functionality requirements and capabilities within. The A11 Radio will learn this information and also record the address node sequence on the MOST bus at this point. This node address list will now be stored within the A11 Radio as the MOST bus configuration (called "Last Working MOST ID of Node 1 - 9" on scan tool data display).

When MOST receive, transmit, or control line faults are detected, transmit/receive messages will not received as expected from the wakeup request. The A11 Radio and the K74 Human Machine Interface Control Module will then perform diagnostics to isolate these MOST faults. If the MOST control line is shorted low to 0 V for excess amount of time, the A11 Radio will set a U2098 DTC and K74 Human Machine Interface Control Module will set a U0029 02 DTC. At this point the MOST bus will be unable to communicate until the shorted MOST control line is repaired.

Once the shorted MOST control line diagnostics pass, the A11 Radio will attempt to resend the initial short pulse attempts up to 3 times on the MOST control line. If the expected responses are not received, the A11 Radio continues into a failure mode setting a U0028 DTC and will continue on to send one 300 ms long pulse, which will enable the furthest upstream transmitting device to become the surrogate MOST Master in this MOST fault/diagnostic mode. When the A11 Radio receives this new MOST Master identity, the surrogate MOST master device can be identified based on scan tool data parameter "Surrogate MOST Master Node Upstream Position". The scan tool should be used to determine the MOST bus configuration and direction by utilizing the "Last Working MOST ID of Node 1 - 9" parameters from the A11 Radio data display. When a fault is present, it will indicate the newly enabled "Surrogate MOST Master Node Upstream Position" from the A11 Radio. This will assist in determining where the MOST bus/control is at fault. The MOST device upstream from the surrogate MOST master device, transmit, receive, or control lines will be the suspect areas for diagnostics at this point. These faults can be associated with any of the MOST transmit, receive, or control line twisted copper wires or possibly an internal device fault.

The K74 Human Machine Interface Control Module will set a U0029 00 DTC when it diagnoses a MOST bus not communicating properly after one attempt. When the DTC U0029 00 is set by the K74 Human Machine Interface Control Module without the corresponding DTC U0028 from the A11 Radio, it will be an indication of an intermittent wiring/device condition.

CAN Graphical Interface (CGI) Circuit Description

This bus is used by the Entertainment sub-system to transfer high-rate display graphics between the A11 Radio and the P17 Info Display Module and/or Radio/HVAC Control. The electrical characteristics of the CAN Graphical Interface (CGI) Bus are very similar to the High Speed GMLAN Bus. The message strategy and construction of messages are different however. Sometimes communication is required between the CAN Graphical Interface Bus and the Low Speed GMLAN Bus. This is accomplished by using the A11 Radio as the Gateway module. Since the CAN Graphical Interface Bus and primary High Speed GMLAN Bus have similar electrical characteristics, the diagnostics for each are similar.

In the case where the P17 Info Display Module and Radio/HVAC Control are separate devices the P17 Info Display Module is responsible for passing information between the A11 Radio and the Radio/HVAC Control. The A11 Radio interfaces only with the P17 Info Display Module and the P17 Info Display Module then communicates with the Radio/HVAC Control through a Local Interconnect Network (LIN) interface.

A bus wake up signal will be generated by the A11 Radio or by the P17 Info Display Module when the system functionality is required. The communication function of the CAN Graphical Interface shall be enabled or disabled based on the voltage level of the Center Stack Wake. The network will stay awake as long as the circuit voltage is driven low, to less than 1.5 V. Communications are disabled with a high circuit voltage around 5.0 V.

The A11 Radio can execute a warm reset of the P17 Info Display Module if the P17 Info Display Module fails to respond to the A11 Radio's request. The Center Stack Reset is a low-asserted pull down output (less than 1.5 V) from the A11 Radio to the P17 Info Display Module and has the same electrical characteristics as those for the Center Stack Wake signal defined above.

Mid Speed GMLAN Circuit Description

The Mid Speed GMLAN Bus is very similar to the High Speed GMLAN Bus except that it uses a slower transmission rate of 125 Kbit/s. This bus is intended for use where the system response time demands that a large amount of data be transmitted in a relatively short amount of time, such as updating a graphics display. As such it has usually been used for infotainment applications. Sometimes communication is required between the Low Speed GMLAN Bus and the Mid Speed GMLAN Bus. This is accomplished by using the A11 Radio as the Gateway module. Since the Mid Speed GMLAN Bus and primary High Speed GMLAN Bus operate in a similar manner, the diagnostics for each are similar.

Low Speed GMLAN Circuit Description

Low Speed GMLAN Bus is used in applications where a high data rate is not required which allows for the use of less complex components. It is typically used for operator controlled functions where the response time requirements are slower than those required for dynamic vehicle control.

The Low Speed GMLAN Serial Data Network consists of a single wire, ground referenced bus with high side voltage drive. During on road vehicle operation data symbols (1's and 0's) are transmitted sequentially at the normal rate of 33.3 Kbit/s. For component programming only, a special high speed data mode of 83.3 Kbit/s may be used.

Unlike the high speed dual wire networks, the single wire low speed network does not use terminating resistors at either end of the network.

The data symbols to be transmitted over the bus are represented by different voltage signals on the bus. When the Low Speed GMLAN Bus is at rest and is not being driven, there is a low signal voltage of approximately 0.2 V. This represents a logic "1". When a logic "0" is to be transmitted, the signal voltage is driven higher to around 4.0 V or higher.

Local Interconnect Network (LIN) Circuit Description

The Local Interconnect Network (LIN) Bus consists of a single wire with a transmission rate of 10.417 Kbit/s. This bus is used to exchange information between a master control module and other smart devices which provide supporting functionality. This type of configuration does not require the capacity or speed of either a High Speed GMLAN Bus or Low Speed GMLAN Bus and is thus relatively simpler.

The data symbols (1's and 0's) to be transmitted are represented by different voltage levels on the communication bus. When the LIN Bus is at rest and is not being driven, the signal is in a high voltage state of approximately Vbatt. This represents a logic "1". When a logic "0" is to be transmitted, the signal voltage is driven low to about ground (0.0 V).

Communication Enable Circuit Description

Devices on High Speed GMLAN Bus enable or disable communication based on the voltage level of the communication enable circuit. When the circuit voltage is high (around 12 V), communications are enabled. When the circuit is low, communications are disabled.

Data Link Connector (DLC)

The X84 Data Link Connector (DLC) is a standardized 16-cavity connector. Connector design and location is dictated by an industry wide standard, and is required to provide the following

  1. Terminal 1 Low speed GMLAN communications terminal
  2. Terminal 2 Class 2 communications terminal
  3. Terminal 3 Mid speed GMLAN serial bus (+) terminal or Object high speed GMLAN serial bus (+) terminal
  4. Terminal 4 Scan tool power ground terminal
  5. Terminal 5 Common signal ground terminal
  6. Terminal 6 High speed GMLAN serial data bus (+) terminal
  7. Terminal 7 Keyword communications terminal
  8. Terminal 11 Mid speed GMLAN serial bus (-) terminal or Object high speed GMLAN serial bus (-) terminal
  9. Terminal 12 Chassis high speed GMLAN serial bus (+) terminal
  10. Terminal 13 Chassis high speed GMLAN serial bus (-) terminal
  11. Terminal 14 High speed GMLAN serial data bus (-) terminal
  12. Terminal 16 Scan tool power, battery positive voltage terminal

Serial Data Reference

The scan tool communicates over the various buses on the vehicle. When a scan tool is installed on a vehicle, the scan tool will try to communicate with every device that could be optioned into the vehicle. If an option is not installed on the vehicle, the scan tool will display No Comm (or Not Connected) for that optional device. In order to avert misdiagnoses of No Communication with a specific device, refer to Data Link References for a list of devices, the buses they communicate with, and the RPO codes for a specific device.

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