Data Communication System: Diagnosis GMC Acadia I рестайлинг

Diagnostic Code Index

DIAGNOSTIC CODE INDEX

Diagnostic Instructions

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

Conditions for Running the DTC

The module 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 module has detected an internal malfunction.

Action Taken When the DTC Sets

The module 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 module ignition cycle counter reaches the reset threshold of 100, without a repeat of the malfunction.

Diagnostic Aids

1. This DTC may be stored as a history DTC without affecting the operation of the control module.
2. Do not replace a control module based only on DTC B1000 being set in history with the exception of the following control modules: Sensing and Diagnostic Module (SDM) Rollover Sensor Passenger Presence System Module
3. If DTC B1000 is set as current, replace the appropriate control module.

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

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

The control module is not configured properly.

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

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

The only requirements are voltage and ground.

The module has detected that the VIN is not programmed.

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

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

1. The control module 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 control module has detected an internal malfunction.

The control module refuses all additional inputs.

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

1. If DTC B101D is set as history or current in the K36 Inflatable Restraint Sensing and Diagnostic Module (SDM) and there are Air Bag or Pretensioner DTC's with symptom byte 02, it is important to repair the deployment loop issue first prior to replacing the K36 SDM. Failure to repair the Air Bag or Pretensioner wiring concern first may cause B101D to reset in the replacement K36 SDM.
2. This DTC may be stored as a history DTC without affecting the operation of the control module.
3. Do not replace a control module based only on DTC B101D being set in history with the exception of the following control modules: K36 Inflatable Restraint Sensing and Diagnostic Module (SDM) K85 Passenger Presence Detection Module
4. If DTC B101D is set as current, replace the appropriate control module.

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

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

The control module is not configured properly.

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

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

The module 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 module has detected an internal malfunction.

The module refuses all additional inputs.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module 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 module.
2. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
3. If this DTC is retrieved as both a current and history DTC, replace the module that set the DTC.

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

Conditions for Running the DTCs

1. Voltage at the modules is in the normal operating voltage 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 module availability has not been received.

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

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

1. Supply voltage at the control modules are in the normal operating range.
2. The vehicle power mode requires serial data communications.

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

1. The ECM/TCM modules turn 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 control module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

DTC Descriptor

Refer to Control Module U Code List .

Diagnostic Fault Information

The system voltage is between 9-16 V.

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

1. Specific subsystems will not function.
2. DTC U0100 in the TCM will cause the transmission to go into default gears.
3. Both DTC U0100 in the TCM and DTC U0101 in the ECM will cause the malfunction indicator lamp (MIL) to illuminate.

1. The ECM/TCM 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 control module 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 control module on the data communication circuit was disconnected while the communication circuit is awake. Power to one or more control modules was interrupted during diagnosis. A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold. Battery power was restored to the vehicle and control modules 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 control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a control module based only on a history U-code.
3. Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication issue.
4. Communication may be available between the BCM and the scan tool with either the low or high speed GMLAN serial data system inoperative. This condition is due to the BCM using both the low and high speed GMLAN systems.
5. Use «Data Link References»(ref-610095-S13212258082014042100000) to determine if the control module uses high or low speed GMLAN serial data communications.
6. Some control modules 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 control module.
7. Some intermittent communication concerns may be caused by fretting corrosion on the serial data circuit terminals. Inspect all connectors at the control module that set the communication DTC, the control module that the communication DTC was set against and any inline harness connectors between the two control modules. Do not replace a control module based only on fretting corrosion. Refer to bulletin 09-06-03-004 for assistance with the diagnosis and repair of this condition.
8. This diagnostic can be used for any control module that is not communicating, regardless of the type of serial data circuit it is connected to, providing the vehicle is equipped with the control module.

Circuit/System Testing

Note. Use the schematic to identify the following: Control modules the vehicle is equipped with Control module locations on the low and high speed GMLAN serial data circuits The control modules B+, ignition, ground, communication enable and serial data circuit terminals

1. Ignition OFF, disconnect the harness connector at of the control module that is not communicating.
2. Test for less than 10 ohms between each ground circuit terminal and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
3. If equipped, ignition ON, verify that a test lamp illuminates between each B+ circuit terminal and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.
4. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.
5. If equipped, ignition ON, verify that a test lamp illuminates between the communication enable circuit terminal OR the accessory wakeup circuit terminal and ground. NOTE: Only the high speed GMLAN modules have a serial data communication enable circuit OR an accessory wakeup serial data circuit and the K9 body control module is the output for these circuits. Refer to the control module schematics to identify which control modules have these circuits. If the test lamp does not illuminate, test the entire circuit, including the B+ circuit to the K9 Body Control Module, for an open/high resistance or short to ground. If the circuits test normal, replace the K9 Body Control Module.
6. Test for less than 4.5 V between each low speed GMLAN serial data circuit terminal and ground. NOTE: The following test step is only applicable to low speed GMLAN modules. If greater than the specified range, refer to «Scan Tool Does Not Communicate with Low Speed GMLAN Device»(ref-610095-S01081384852014042100000) to test for a short to voltage in the serial data circuit.
7. Ignition OFF, all access doors closed, all vehicle systems OFF and all keys at least 3 meters away from vehicle. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 5 ohms between the serial data circuit terminals and the appropriate X84 data link connector (DLC) terminal listed below: Class 2 serial data circuit terminal 2 Low speed GMLAN serial data terminal 1 High speed GMLAN serial data terminal 6 or 14 Mid speed GMLAN serial data terminal 3 or 11 Chassis high speed GMLAN serial data terminal 12 or 13 If greater than the specified range, test the serial data circuit for an open/high resistance between the non communicating control module and a module setting the DTC or a serial data splice pack.
8. Test for less than 130 ohms between each pair of high speed GMLAN serial data circuits. NOTE: The following test step is only applicable to high speed GMLAN modules. If greater than the specified range, refer to «Scan Tool Does Not Communicate with High Speed GMLAN Device»(ref-610095-S42116014012014042100000) to test for an open/high resistance in the serial data circuit.
9. If all circuits test normal, replace the control module that is not communicating.

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

Refer to Control Module U Code List .

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

The control module is not configured properly.

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

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

The system voltage is between 9-16 V.

U1500 01

When there is a short to voltage in the local interconnect network bus circuit.

U1500 02

When there is a short to ground in the local interconnect network bus circuit.

U1500 31

The module has detected an internal malfunction.

U1511, U1512

The DTC will set when there is an open/high resistance in the local interconnect network bus circuit or an open in the voltage or ground circuits of the motor or module.

U1500

The individual LIN bus will be inoperative, disabling all windows on one side of the vehicle.

U1500 31

The module refuses all additional inputs.

U1511

1. If set in the driver door lock window switch or passenger door lock window switch, no window on the specific side of the vehicle will operate if the open is before the first splice from the door module and both DTC U1511 and U1512 should set. If open after the first splice, the individual window will be inoperative and a single DTC should set.
2. If set in the BCM, the compass is inoperative in the DIC.

U1512

No window on the specific side of the vehicle will operate if the open is before the first splice from the door module and both DTC U1511 and U1512 should set. If open after the first splice, the individual window will be inoperative and a single DTC should set.

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

1. A window regulator motor may cause a short to the local interconnect network bus circuit and will cause all windows on one side to be inoperative.
2. An open/high resistance between the door module and the first splice from the module will cause all windows on one side to be inoperative.
3. An open/high resistance between the window regulator motor and the first splice from the motor will cause only one window to be inoperative.

Compass Malfunction Test

1. Ignition OFF, disconnect the harness connector at the electronic compass module.
2. Ignition OFF, test for less than 5.0 ohms between the ground circuit terminal 2 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal 1 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
4. Test for 6.0-7.0 V between the LIN Bus circuit terminal 3 and ground. If greater than the specified range, test the LIN Bus circuit for a short to voltage. If the circuit tests normal, replace the BCM. If less than the specified range, test the LIN Bus circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
5. If all circuits test normal, replace the electronic compass module.

Window Malfunction Test

1. Ignition OFF, disconnect the harness connector at the appropriate window motor.
2. Ignition OFF, test for less than 2.0 ohms between the ground circuit terminal 4 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify a test lamp illuminates between the B+ circuit terminal 3 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
4. Test for 6.0-7.0 V between the LIN circuit terminal 5 and ground. If greater than the specified range, test the LIN circuit for a short to voltage. If the circuit tests normal, replace the door module. If less than the specified range, test the LIN circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the door module.
5. If all circuits test normal, replace the window motor.

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

Refer to Control Module U Code List .

1. A control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a control module based only on a history U-code.
2. Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication issue.
3. 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 control modules on the LIN bus network.
4. An open in the LIN bus serial data circuit between the splice pack and a module will only affect that specific module. This type of failure will set a loss of communication DTC for each control module affected and the other control modules will still communicate.
5. Some intermittent communication concerns may be caused by fretting corrosion on the serial data circuit terminals. Inspect all connectors at the control module that set the communication DTC, the control module that the communication DTC was set against and any inline harness connectors between the two control modules. Do not replace a control module based only on fretting corrosion. Refer to bulletin 09-06-03-004 for assistance with the diagnosis and repair of this condition..

Note. Use the schematic to identify the following: LIN devices the vehicle are equipped with The LIN device's B+, ignition, ground and serial data circuit terminals Use the Control Module U-Code list to determine which control module is not communicating with the master control module. Refer to Control Module U Code List . A loss of serial data communications DTC does not represent a failure of the master control module that set it.

1. Ignition OFF, 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 greater than the specified range, test the ground circuit for an open/high resistance.
3. If equipped, verify that a test lamp illuminates between each B+ circuit terminal and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the LIN device for a short to ground. If the circuits test normal, replace the LIN device.
4. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the LIN device for a short to ground. If the circuits test normal, replace the LIN device.
5. Ignition ON, test for 2-12 V between the LIN serial data circuit and ground. If greater than the specified range, test the LIN serial data circuit for a short to voltage. If the circuit tests normal, replace the master control module. If less than the specified range, test the LIN serial data circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the master control module.
6. If all circuits test normal, replace the LIN device.

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

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

The BCM senses a short to ground on the accessory wake up serial data circuit.

1. The modules use a default value for the missing parameters until the next ignition cycle.
2. The modules is never signaled, therefore the specific subsystems will not function.
3. The vehicle may not start.

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

1. Short to ground may open the fuse feeding the ignition switch.
2. Short to ground may also set multiple no communication DTCs for GMLAN high speed modules.

1. Ignition OFF, disconnect the X1 harness connector at the ECM and the TCM one at a time. After each disconnect, test for current DTCs. DTC U1814 should remain current. If the DTC becomes history, replace the module disconnected when the DTC became history.
2. Ignition OFF, disconnect the X4 harness connector at the BCM.
3. Test for infinite resistance between the signal circuit terminal 19 and ground. If less than the specified value, test the signal circuit for a short to ground.
4. If all circuits tests normal, replace the BCM.

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

1. The system voltage is between 9-16 volts.
2. The BCM attempts to enable the modules connected to the high speed GMLAN serial data wake up circuit.

The BCM senses a short to ground on the serial data wake up circuit.

1. The output command is turned off while the malfunction is present.
2. The modules use a default value for the missing parameters.
3. The modules are never signaled, therefore the specific subsystems 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 module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Short to ground will also set multiple history no communication DTCs for GMLAN high speed modules.

1. Ignition OFF, disconnect the harness connector at the following modules one at a time. After each disconnect, clear the DTC, cycle the ignition key 3 times, then test for the DTC. DTC U2099 should remain current. EBCM Transfer case control module If the DTC becomes history, replace the last module disconnected when the DTC became history.
2. Ignition OFF, disconnect the X3 harness connector at the BCM.
3. With the modules still disconnected, test for infinite resistance between BCM X3 terminal 19 and ground. If less than the specified value, test the circuit for a short to ground.
4. If all circuits test normal and the DTC is set as current, replace the BCM.

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

Circuit Description

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

DTC U2103 will set when fewer modules are detected on the buss before the modules can learn the other module IDs. If the communication buss is opened or if the module power supply is lost when the vehicle is in the OFF power mode and then placed in the RUN power mode, U2103 will set in specific modules.

1. Voltage supplied to the modules is in the normal operating voltage 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 module availability has not been received.

The module 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 module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. Diagnosis of this DTC is accomplished via the symptom, «DTC U0100-U02FF»(ref-610095-S35712348932014042100000) .
2. An intermittent condition is likely to be caused by a short on the GMLAN serial data circuits. Use the «DTC U0100-U02FF»(ref-610095-S35712348932014042100000) procedure in order to isolate an intermittent condition.

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

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

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

1. The vehicle stability enhancement system (VSES), if equipped and traction control system (TCS) will not function.
2. System OFF lamps will illuminate for these systems.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module 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 control module on the data communication circuit was disconnected while the communication circuit is awake. Power to one or more modules was interrupted during diagnosis. A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold. Battery power was restored to the vehicle and control modules 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 control module may have a U code stored in history that does not require any repairs. Issues with late or corrupted messages between control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a control module based only on a history U code.
3. Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication issue.
4. Communication may be available between the BCM and the scan tool with either the low or high speed GMLAN serial data system inoperative. This condition is due to the BCM using both the low and high speed GMLAN systems.
5. Use to determine if the module uses high or low speed GMLAN serial data communications.
6. Some control modules 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 control module.
7. This diagnostic can be used for any control module that is not communicating, regardless of the type of serial data circuit it is connected to, providing the vehicle is equipped with the control module.

Only DTC C0710 is set

1. Ignition OFF and all vehicle systems OFF. Disconnect the harness connectors at the steering wheel speed position sensor. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 10 ohms between the low reference circuit terminal 6 and ground. If 10 ohms or greater Repair the open/high resistance in the circuit between the X201 inline connector and the steering wheel speed position sensor. If less than 10 ohms
3. Ignition ON.
4. Verify a test lamp illuminates between the ignition circuit terminal 5 and ground. If the test lamp does not illuminate Repair the open/high resistance in the circuit between the X201 inline connector and the steering wheel speed position sensor. If the test lamp illuminates
5. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down.
6. Test for less than 70 ohms between the serial data circuits terminal 2 and 3. If 70 ohms or greater Repair the open/high resistance in the circuits between the X201 inline connector and the steering wheel speed position sensor. If less than 70 ohms
7. Replace the steering wheel speed position sensor.

Only DTC U2142 is set

1. Ignition OFF and all vehicle systems OFF. Disconnect the harness connectors at the yaw and lateral accelerometer sensor. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 10 ohms between the low reference circuit terminal 1 and ground. If 10 ohms or greater Repair the open/high resistance in the circuit between the X201 inline connector and the yaw and lateral accelerometer sensor. If less than 10 ohms
3. Ignition ON.
4. Verify a test lamp illuminates between the ignition circuit terminal 4 and ground. If the test lamp does not illuminate Repair the open/high resistance in the circuit between the X201 inline connector and the yaw and lateral accelerometer sensor. If the test lamp illuminates
5. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down.
6. Test for less than 130 ohms between the serial data circuits terminal 2 and 3. If 130 ohms or greater Repair the open/high resistance in the circuits between the X201 inline connector and the yaw and lateral accelerometer sensor. If less than 130 ohms
7. Replace the yaw and lateral accelerometer sensor.

Both DTC C0710 and U2142 are set

1. Ignition OFF and all vehicle systems OFF. Disconnect the harness connectors at the steering wheel speed position sensor. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 10 ohms between the low reference circuit terminal 6 and ground. If 10 ohms or greater Ignition OFF, disconnect the harness connector at the electronic brake control module. Test for less than 2 ohms in the low reference circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit between the splice and the electronic brake control module. If less than 2 ohms, replace the electronic brake control module. If less than 10 ohms
3. Ignition ON.
4. Verify a test lamp illuminates between the ignition circuit terminal 5 and ground. If the test lamp does not illuminate Ignition OFF, disconnect the harness connectors at the yaw and lateral accelerometer sensor, ignition ON. Verify a test lamp illuminates between the ignition circuit and ground. If the test lamp illuminates, replace the yaw and lateral accelerometer sensor. If the test lamp does not illuminate Ignition OFF, disconnect the harness connectors at the electronic brake control module. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short ground on the circuit. If infinite resistance Test for less than 2 ohms in the ignition circuit end to end between the steering wheel speed position sensor and the electronic brake control module terminal 32. If greater than 2 ohms, repair the open/high resistance in the circuit. If less than 2 ohms, replace the electronic brake control module. If the test lamp illuminates
5. Test for less than 4.5 V between the serial data circuits listed below and ground. Terminal 2 Terminal 3 If 4.5 V or greater Ignition OFF, disconnect the harness connectors at the yaw and lateral accelerometer sensor, ignition ON. Test for less than 4.5 V between the serial data circuit and ground. If 4.5 V or less, replace the yaw and lateral accelerometer sensor. If greater than 4.5 V Ignition OFF, disconnect the harness connectors at the electronic brake control module, 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, replace the electronic brake control module. If less than 4.5 V
6. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down.
7. Test for greater than 100 ohms between the serial data circuits listed below and ground. Terminal 2 Terminal 3 If 100 ohms or less Ignition OFF, disconnect the harness connectors at the electronic brake control module. Test for greater than 100 ohms between the serial data circuit and ground. If 100 ohms or greater, replace the electronic brake control module. If less than 100 ohms Disconnect the harness connectors at the yaw and lateral accelerometer sensor. 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, replace the yaw and lateral accelerometer sensor. If greater than 100 ohms
8. Test for 50-70 ohms between the serial data circuits terminal 2 and 3. If less than 50 ohms Ignition OFF, disconnect the harness connectors at the electronic brake control module. Test for greater than 110 ohms between the serial data circuits. If 110 ohms or greater, replace the electronic brake control module. If less than 110 ohms Disconnect the harness connectors at the yaw and lateral accelerometer sensor. Test for infinite resistance between the serial data circuits. If less than infinite resistance, repair the short between the circuits. If infinite resistance, replace the yaw and lateral accelerometer sensor. If greater than 70 ohms Ignition OFF, disconnect the harness connectors at the electronic brake control module. Test for less than 2 ohms in the serial data circuits listed below end to end. The steering wheel speed position sensor terminal 2 and the electronic brake control module terminal 24 The steering wheel speed position sensor terminal 3 and the electronic brake control module terminal 37 If greater than 2 ohms, repair the open/high resistance in the circuit. If less than 2 ohms Test for less than 130 ohms between the serial data circuits terminal 2 and 3. If 130 ohms or less, replace the electronic brake control module. If greater than 130 ohms Disconnect the harness connectors at the yaw and lateral accelerometer sensor. Test for less than 2 ohms in the serial data circuits listed below end to end. The steering wheel speed position sensor terminal 2 and the yaw and lateral accelerometer sensor terminal 2 The steering wheel speed position sensor terminal 3 and the yaw and lateral accelerometer sensor terminal 3 If greater than 2 ohms, repair the open/high resistance in the circuit. If less than 2 ohms, replace the yaw and lateral accelerometer sensor. If between 50-70 ohms
9. Replace the steering wheel speed position sensor.

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the systems. Refer to «Checking Aftermarket Accessories»(ref-610066-S23886117082014042100000) .
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

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»(ref-610095-S36384473822014042100000)
2. «Scan Tool Does Not Communicate with High Speed GMLAN Device»(ref-610095-S42116014012014042100000)
3. «Scan Tool Does Not Communicate with Low Speed GMLAN Device»(ref-610095-S01081384852014042100000)

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

1. The scan tool will power up with the ignition OFF. Some modules however, will not communicate unless the ignition is ON and the power mode master (PMM) module sends the appropriate power mode message.
2. If the B+ circuit, ground circuits and connections of the DLC are functioning properly, the malfunction must be due to the scan tool/CANdi module.

1. Test for less than 2.0 ohms between the ground circuits terminal 4 of the DLC and ground and terminal 5 of the DLC and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
2. Ignition ON, verify a test lamp illuminates between the B+ circuit terminal 16 at the DLC and ground. If the test lamp does not illuminate, test the voltage supply circuit for a short to ground or an open/high resistance.
3. If all circuits test normal, refer to the scan tool/CANdi module user guide.

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

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 control module on the data communication circuit was disconnected while the communication circuit is awake. Power to one or more modules was interrupted during diagnosis A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold. Battery power was restored to the vehicle and control modules 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 control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication issue.
3. Communication may be available between the body control module (BCM) and the scan tool with the high speed GMLAN serial data system inoperative. This condition is due to the BCM using both the high and low speed GMLAN systems.
4. An open in the DLC ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle. When the scan tool attempts to communicate with the vehicle a message "no CANdi module detected" will be displayed.
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. Tire Pressure Monitor (TPM) system warning lights.

Note. Each control module may need to be disconnected to isolate a circuit fault. Use the schematic and component connector end views to identify the following: Control modules the vehicle is equipped with High speed GMLAN serial data circuit terminating resistors Control module locations on the high speed GMLAN serial data circuits Each control module's high speed GMLAN serial data circuit terminals

1. Attempt to communicate with all control modules on the high speed GMLAN serial data circuit, refer to «Data Link References»(ref-610095-S13212258082014042100000) . Communications should not be available with two or more control modules on the high speed GMLAN serial data circuit. If only one control module is not communicating, diagnose that control module only; refer to «DTC U0100-U02FF»(ref-610095-S35712348932014042100000) .
2. Disconnect the scan tool from the DLC. The following tests will be done at the DLC connector.
3. All access doors closed, ignition OFF for 60 seconds, test for less than 10 ohms between the ground circuit terminal 5 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
4. Ignition ON, test for less than 4.5 V between the serial data circuits listed below and ground: Terminal 6 Terminal 14 If greater than the specified range, test the serial data circuit for a short to voltage; refer to «Testing the Serial Data Circuits for a Short to Voltage»(ref-610095-S17389949912014071100000) .
5. Ignition OFF for 60 seconds, test for greater than 100 ohms between the serial data circuits listed below and ground: Terminal 6 Terminal 14 If less than the specified range, test the serial data circuit for a short to ground; refer to «Testing the Serial Data Circuits for a Short to Ground»(ref-610095-S00988665092014071100000) .
6. Test for 50-70 ohms between the serial data circuits terminal 6 and terminal 14. If less than 35 ohms, test for a short between the serial data circuits; refer to «Testing the Serial Data Circuits for a Short between the Circuits»(ref-610095-S33033146252014071100000) . If 35-50 ohms there may be a third terminating resistor between the serial data circuits. This can happen if the incorrect control module is installed. Some control modules are available with and without the terminating resistors installed to reduce the need of terminating resistors in the wiring harness. If greater than 70 ohms but less than infinite, test the serial data circuit for an open/high resistance; refer to «Testing the Serial Data Circuits for an Open/High Resistance»(ref-610095-S13975537352014071100000) . If infinite, test the serial data circuits between the DLC and the first connection to the serial data circuit for an open/high resistance.

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 control module.
2. Ignition ON, test for greater than 4.5 V between each serial data circuit at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are greater than 4.5 V. If all serial data circuits are less than the specified range, replace the control module that was disconnected.
3. Ignition OFF, disconnect the harness connectors with the high speed GMLAN serial data circuits at another control module, in the direction of the circuit shorted to voltage.
4. Ignition ON, test for greater than 4.5 V between the serial data circuits at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are greater than 4.5 V. If all serial data circuits are less than the specified range, replace the control module that was just disconnected.
5. Repeat step 3 until one of the follow conditions are isolated: A short to voltage on the serial data circuit between 2 control modules A short to voltage on the serial data circuit between a control module and a terminating resistor.

Testing the Serial Data Circuits for a Short to Ground

1. Ignition OFF, disconnect the harness connectors with the high speed GMLAN serial data circuits at an easily accessible control module.
2. Ignition OFF for 60 seconds, test for less than 1k ohms between each serial data circuit at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are less than 1k ohms. If all serial data circuits are greater than the specified range, replace the control module that was disconnected.
3. Disconnect the harness connectors with the high speed GMLAN serial data circuits at another control module, in the direction of the circuit shorted to ground.
4. Ignition OFF for 60 seconds, test for less than 1k ohms between the serial data circuits at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are less than 1k ohms. If greater than the specified range for all serial data circuits, replace the control module that was just disconnected.
5. Repeat step 3 until one of the follow conditions are isolated: A short to ground on the serial data circuit between 2 control modules A short to ground on the serial data circuit between a control module and a terminating resistor

Testing the Serial Data Circuits for a Short between the Circuits

1. Ignition OFF, disconnect the harness connectors with the high speed GMLAN serial data circuits at an easily accessible control module that is not communicating.
2. Ignition OFF for 60 seconds, test for less than 35 ohms between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are less than 35 ohms. If each pair of serial data circuits is greater than the specified range, replace the control module that was disconnected.
3. Connect the harness connectors at the control module that was disconnected.
4. Disconnect the harness connectors with the high speed GMLAN serial data circuits at another control module, in the direction of the circuits shorted together.
5. Ignition OFF for 60 seconds, test for less than 35 ohms between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are less than 35 ohms. If each pair of serial data circuits is within the specified range, replace the control module that was just disconnected.
6. Repeat step 3 until one of the following conditions are isolated: Serial data circuits shorted together between 2 control modules Serial data circuits shorted together between a control module and a terminating resistor A shorted terminating resistor

Testing the Serial Data Circuits for an Open/High Resistance

1. Ignition OFF, disconnect the harness connectors with the high speed GMLAN serial data circuits at an easily accessible control module that is not communicating.
2. Ignition OFF for 60 seconds, test for greater than 130 ohms between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are greater than 130 ohms. If each pair of serial data circuits is less than the specified range, replace the control module that was disconnected.
3. Connect the harness connectors at the control module that was disconnected.
4. Disconnect the harness connectors with the high speed GMLAN serial data circuits at another control module, in the direction of the open circuit.
5. Ignition OFF for 60 seconds, test for greater than 130 ohms between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are greater than 130 ohms. If each pair of serial data circuits is less than the specified range, replace the control module that was just disconnected.
6. Repeat step 3 until one of the following conditions are isolated: An open/high resistance on the serial data circuit between 2 control modules An open/high resistance on the serial data circuit between a control module and a terminating resistor An open/high resistance terminating resistor

1. Perform the «Diagnostic System Check - Vehicle»(ref-610038-S36414632882014042100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-610038-S01145188892014042100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-610038-S00675927362014042100000) provides an overview of each diagnostic category.

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 control module on the data communication circuit was disconnected while the communication circuit is awake. Power to one or more modules was interrupted during diagnosis A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold. Battery power was restored to the vehicle and control modules 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 control module reporting a U code. The U code identifies which control module needs to be diagnosed for a communication issue.
3. Communication may be available between the BCM and the scan tool with the high speed GMLAN serial data system inoperative. This condition is due to the BCM using both the high and low speed GMLAN systems.
4. An open in the DLC ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle. When the scan tool attempts to communicate with the vehicle a message "no CANdi module detected" will be displayed.
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. The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus. 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. Tire Pressure Monitor (TPM) system warning lights.

Note. Use the schematic to identify the following: Control modules the vehicle is equipped with Control module locations on the low speed GMLAN serial data circuit Each control module's low speed GMLAN serial data circuit terminals

1. Attempt to communicate with all control modules on the low speed GMLAN serial data circuit, refer to «Data Link References»(ref-610095-S13212258082014042100000) . Communications should not be available with two or more control modules on the low speed GMLAN serial data circuit. If only one control module is not communicating, diagnose that control module only, refer to «DTC U0100-U02FF»(ref-610095-S35712348932014042100000) . If one or more control modules are communicating but not all, refer to «Testing the Serial Data Circuit for an Open/High Resistance»(ref-610095-S03163675222014071100000) .
2. Disconnect the scan tool from the DLC. The following tests will be done at the DLC connector.
3. All access doors closed, ignition OFF for 60 seconds, test for less than 10 ohms between the ground circuit terminal 5 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
4. Ignition ON, test for less than 4.5 V between the serial data circuit terminal 1 and ground. If greater than the specified range, test the serial data circuit for a short to voltage, refer to «Testing the Serial Data Circuits for a Short to Voltage»(ref-610095-S28084940852014071100000) .
5. Ignition OFF for 60 seconds, test for greater than 100 ohms between the serial data circuit terminal 1 and ground. If not the specified value, test the serial data circuit for a short to ground, refer to «Testing the Serial Data Circuits for a Short to Ground»(ref-610095-S27671708182014071100000) .
6. Disconnect the harness connector at the JX 205 splice pack.
7. Test for less than 2 ohms between the serial data circuit terminal 1 and the JX 205 splice pack terminal 1. If greater than the specified range, test the serial data circuit for an open/high resistance. If the circuits test normal, replace the splice pack.

1. Ignition OFF, disconnect the harness connectors at the JX 205 and JX 405 splice packs, as equipped.
2. Ignition ON, test for less than 4.5 V between the DLC serial data circuit terminal 1 and ground. If greater than the specified range, repair the short to voltage.
3. Test for less than 4.5 V between each serial data circuit and ground. If greater than the specified range, perform the appropriate test listed below: Serial data circuits with one control module, test the serial data circuit for a short to voltage. If the circuit tests normal replace the control module. Serial data circuits with 2 or more control modules, test each section of the serial data circuit for a short to voltage. If the circuits test normal, replace the control module that causes the short to voltage when connected.

1. Ignition OFF, disconnect the harness connectors at the JX 205 and JX 405 splice packs, as equipped.
2. Test for infinite resistance between the DLC serial data circuit terminal 1 and ground. If not the specified value, repair the short to ground.
3. Ignition OFF for 60 seconds, test for greater than 100 ohms between each serial data circuit and ground. If less than the specified range, perform the appropriate test listed below: Serial data circuits with one control module, test the serial data circuit for a short to ground. If the circuit tests normal replace the control module. Serial data circuits with 2 or more control modules, test each section of the serial data circuit for a short to ground. If the circuits test normal, replace the control module that causes the short to ground when connected.

Testing the Serial Data Circuit for an Open/High Resistance

1. If equipped with a JX 405 splice pack, ignition ON, verify the scan tool communicates with one or more control modules connected to the JX 405 splice pack. If all control modules on the JX 405 spice pack do not communicate, test the serial data circuit between the JX 205 and JX 405 splice packs for an open/high resistance. If the circuit tests normal, test each splice pack for an open/high resistance.
2. Ignition OFF, disconnect one of the harness connectors listed below: JX 205 if the control modules not communicating are connected to the JX 205 splice pack JX 405 if the control modules not communicating are connected to the JX 405 splice pack
3. Install a 3A fused jumper wire between the disconnected splice pack terminal 1 and a low speed GMLAN serial data circuit that is not communicating.
4. Ignition ON, verify the scan tool communicates with the control modules connected to the low speed GMLAN serial data circuit. If any control module does not communicate, test each section of the serial data circuit for an open/high resistance. If the circuits test normal, replace the control module that does not communicate when connected.

The communication among control modules is performed primarily through the GMLAN high speed serial data circuit and the GMLAN low speed serial data circuits. The modules that need real time communication are attached to the high speed GMLAN network. The body control module (BCM) is the serial data gateway between the networks. The purpose of the gateway is to translate serial data messages between the GMLAN high speed buss and the GMLAN low speed buss. The controller area network (CAN) is another serial data communication network used on this vehicle which is dedicated to the electronic brake control module (EBCM) subsystem for stabilization. Below are more detailed descriptions of the individual networks. The gateway will interact with each network according to that network's transmission protocol. Refer to Body Control System Description and Operation for more information about the gateway.

GMLAN High Speed Circuit Description

The data link connector (DLC) allows a scan tool to communicate with the high speed GMLAN serial data circuit. The serial data is transmitted on two twisted wires that allow speed 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 is after the BCM in either the AWD module or a separate resistor connector assembly. The resistors are used to reduce noise on the High Speed GMLAN buss 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. The idle level, which is approximately 2.5 volts, is considered recessive transmitted data and is interpreted as a logic 1. Driving the lines to their extremes, adds one volt to the high speed GMLAN serial data bus (+) and subtracts one volt from the high speed GMLAN serial data bus (-) wire. This dominant state is interpreted as a logic 0. GMLAN network management supports selective start up and is based on virtual networks. A virtual network is a collection of signals started in response to a vehicle event. The starting of a virtual network signifies that a particular aspect of the vehicles functionality has been requested. A virtual network is supported by virtual devices, which represents a collection of signals owned by a single physical device. So, any physical device can have one or more virtual devices. The signal supervision is the process of determining whether an expected signal is being received or not. Fail-softing is the ability to substitute a signal with a default value or a default algorithm, in the absence of a valid signal. Some messages are also interpreted as a heartbeat of a virtual device. If such a signal is lost, the application will set a no communication code against the respective virtual device. This code is mapped on the Tech 2 screen as a code against the physical device.

GMLAN Low Speed Circuit Description

The data link connector (DLC) allows a scan tool to communicate with the low speed GMLAN serial data circuit. The serial data is transmitted over a single wire to the appropriate control modules. The transmission speed for GMLAN low speed is up to 83.33 Kb/s. Under normal vehicle operating conditions, the speed of the buss is 33.33 Kb/s. This protocol produces a simple pulse train sent out over the GMLAN low speed serial data bus. When a module pulls the buss high, 5 volts, this creates a dominant logic state or 0 on the buss. When the buss is pulled low, 0 volts, it is translated as a recessive logic state or 1. To wake the control modules connected to the GMLAN low speed serial data buss, a voltage wake up pulse is sent out over the buss, the voltage level of the pules is +10 volts. Modules connected to the GMLAN low speed buss can be part of a virtual network as described in the previous paragraph. The modules on the GMLAN low speed serial data buss are connected to the buss in a parallel configuration.