Data Communication System: Diagnosis Chevrolet Spark M300

Diagnostic Code Index

DIAGNOSTIC CODE INDEX

Diagnostic Instructions

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

DTC Descriptor

For symptom byte information, refer to Symptom Byte List .

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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

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 Detection Module
3. If DTC B101D is set as current, replace the appropriate device.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

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, P0602, P0603, P0604, P0606, and P062F are Type A DTCs.

DTCs P0601, P0602, P0603, P0604, P0606, and P062F are Type A DTCs.

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

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) 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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

DTC Descriptors

For symptom byte information, refer to Symptom Byte List .

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.

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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

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 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. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

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»(ref-544492-S32517214662013042400000) 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.

Circuit/System Testing

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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

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. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

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

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 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»(ref-544492-S32517214662013042400000) 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.

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. Disconnect all the harness connectors at the device that is not communicating. 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 disconnected device. 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 disconnected device. If the test lamp illuminates
7. Ignition ON.
8. 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
9. Test for less than 4.5 V between each low speed GMLAN serial data circuit terminal and ground. If 4.5 V or greater Refer to «Scan Tool Does Not Communicate with Low Speed GMLAN Device»(ref-544492-S21783918672013042400000) to test for a short to voltage in the serial data circuit. If less than 4.5 V
10. 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.
11. Test for less than 2 ohms in each of the 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
12. 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»(ref-544492-S26875200312013042400000) 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»(ref-544492-S26875200312013042400000) to test for an open/high resistance in the serial data circuit. If between 110-130 ohms
13. Replace the device that is not communicating.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) 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 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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) 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 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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

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

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.

Note. 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. Disconnect the harness connector at a LIN device that is not communicating. 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. 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. 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 LIN device. If the test lamp illuminates
5. Ignition ON.
6. 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. 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 LIN device. If the test lamp illuminates
7. Ignition ON.
8. 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, 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
9. Ignition ON.
10. Test for 2-13 V between the LIN serial data circuit terminal and ground. If less than 2 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. 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
11. Replace the disconnected LIN device.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

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.

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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

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.

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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List .

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.

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the systems. Refer to «Checking Aftermarket Accessories»(ref-544474-S17151285262013042400000) .
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-544492-S19652977582013042400000)
2. «Scan Tool Does Not Communicate with High Speed GMLAN Device»(ref-544492-S26875200312013042400000)
3. «Scan Tool Does Not Communicate with Low Speed GMLAN Device»(ref-544492-S21783918672013042400000)
4. «Scan Tool Does Not Communicate with Chassis High Speed GMLAN Device»(ref-544492-S22472375712013042400000)

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) provides an overview of each diagnostic category.

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.

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»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) 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 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).

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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) 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 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

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.

1. Perform the «Diagnostic System Check - Vehicle»(ref-544470-S31312478522013042400000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-544470-S20767567702013042400000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-544470-S33594679972013042400000) 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 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 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

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 greater than 2 ohms between each section of the failed serial data circuit and ground. If 2 ohms or less, repair the short to ground in the circuit. If greater than 2 ohms 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.

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.