Instrument Cluster Diagnostic Trouble Codes (Chevrolet Captiva 1)

• One of the low speed GMLAN serial data lines is shorted to ground or supply voltage.
• An internal fault in one of the controllers causing a short to supply voltage or to ground in the low-speed GMLAN communication lines.

• Controller supply voltages are within normal operating range
• The vehicle's power mode requires serial data exchange to operate.
• DTC U0073 does not have a current status

• This fault code may be generated due to a contact problem in the failed controller.
• This fault code may be generated due to a power failure to the controller.

• The vehicle power mode master device requires serial data exchange to operate.
• The vehicle's power mode requires serial data exchange to operate.

• The current fault code is cleared once the fault has disappeared.
• The fault code is cleared from the history when the ignition cycle counter in the controller reaches the reset threshold of 50 without the fault recurring.

• Using the above list of fault code definitions, determine which controller is experiencing communication problems.
• If there are multiple controllers with communication problems, select the one closest to the diagnostic connector (DLC).
• Using the communication line list, determine whether the GMLAN serial communication line used on the controller is high speed or low speed.
• Some controllers do not have internal protection for certain voltage outputs and may cause the battery positive voltage fuse or ignition voltage supply to blow. If the input voltage fuse is blown but no short circuit is detected in that circuit, make sure there are no shorted to ground voltage output circuits on the controllers before replacing the controller.
• This diagnostic can be used on any module that is required to communicate over the high or low speed GMLAN serial data line, provided the vehicle is equipped with an option that uses that module.

1. Use the above list of fault code definitions and diagnostic recommendations to determine which controller with the communication problem needs to be tested.
2. Turn off the ignition, disconnect the wiring harness connector on the controller where the connection is broken.

Important: Only high speed GMLAN controllers have a serial communications enable circuit OR an auxiliary serial communications wake-up circuit. Refer to the controller schematics to determine which controllers have these circuits. If the controller with the communication problem is missing one of these circuits, go to step 4.

3. Turn ignition ON, verify that the test lamp illuminates between the serial data line enable circuit OR the auxiliary serial data line wake-up circuit and ground.
• If the test lamp does not light, repair the open or high resistance in the circuit. If there are no faults in the circuits, replace the BCM.

4. Turn on the ignition, check if the test lamp lights between all positive battery voltage circuits and ground.
• If the test lamp does not light, eliminate the short to ground or open/high resistance in the circuit. If the circuit fuse is blown, also check the positive voltage outputs on the controller for a short to ground. If the circuits are OK, replace the faulty controller.

5. Check if the test lamp lights between all ignition voltage circuits and ground.
• If the test lamp does not light, eliminate the short to ground or open/high resistance in the circuit. If the circuit fuse is blown, also check the positive voltage outputs on the controller for a short to ground. If the circuits are OK, replace the faulty controller.

6. Check that the resistance between the controller ground circuits and the ground is no higher than 1 Ohm.
• If it is higher than 1 Ohm, repair the open circuit in the ground circuit.

7. Using the communication line list, determine if the controller with the communication problem is using a low speed GMLAN serial communication line.
• If the controller uses only high speed GMLAN communication line, replace the controller.

8. Verify that the resistance in the low speed GMLAN serial data line between the controller with the communication problem and the controller setting the fault code is less than 1 ohm.





• If the resistance is greater than 1 ohm, test the low speed GMLAN serial data circuit for an open or high resistance.

9. If all circuits are OK, replace the controller with communication problems.

• The voltage in the system is 9 - 16 V.
• The vehicle power mode master device requires serial data exchange to operate.

• The current fault code is cleared once the fault has disappeared.
• The fault code is cleared from the history when the ignition cycle counter in the controller reaches the reset threshold of 50 without the fault recurring.

• Using the above list of fault code definitions, determine which controller is experiencing communication problems.
• If there are multiple controllers with communication problems, select the one closest to the diagnostic connector (DLC).
• Using the communication line list, determine whether the GMLAN serial communication line used on the controller is high speed or low speed.
• Some controllers do not have internal protection for certain voltage outputs and may cause the battery positive voltage fuse or ignition voltage supply to blow. If the input voltage fuse is blown but no short circuit is detected in that circuit, make sure there are no shorted to ground voltage output circuits on the controllers before replacing the controller.
• This diagnostic can be used on any module that is required to communicate over the high or low speed GMLAN serial data line, provided the vehicle is equipped with an option that uses that module.

1. Use the above list of fault code definitions and diagnostic recommendations to determine which controller with the communication problem needs to be tested.
2. Turn off the ignition, disconnect the wiring harness connector on the controller where the connection is broken.

Important: Only high speed GMLAN controllers have a serial communications enable circuit OR an auxiliary serial communications wake-up circuit. Refer to the controller schematics to determine which controllers have these circuits. If the controller with the communication problem is missing one of these circuits, go to step 4.

3. Turn ignition ON, verify that the test lamp illuminates between the serial data line enable circuit OR the auxiliary serial data line wake-up circuit and ground.
• If the test lamp does not light, repair the open or high resistance in the circuit. If there are no faults in the circuits, replace the BCM.

4. Turn on the ignition, check if the test lamp lights between all positive battery voltage circuits and ground.
• If the test lamp does not light, eliminate the short to ground or open/high resistance in the circuit. If the circuit fuse is blown, also check the positive voltage outputs on the controller for a short to ground. If the circuits are OK, replace the faulty controller.

5. Check if the test lamp lights between all ignition voltage circuits and ground.
• If the test lamp does not light, eliminate the short to ground or open/high resistance in the circuit. If the circuit fuse is blown, also check the positive voltage outputs on the controller for a short to ground. If the circuits are OK, replace the faulty controller.

6. Check that the resistance between the controller ground circuits and the ground is no higher than 1 Ohm.
• If it is higher than 1 Ohm, repair the open circuit in the ground circuit.

7. Using the communication line list, determine if the controller with the communication problem is using a low speed GMLAN serial communication line.
• If the controller uses only high speed GMLAN communication line, replace the controller.

8. Verify that the resistance in the low speed GMLAN serial data line between the controller with the communication problem and the controller setting the fault code is less than 1 ohm.
• If the resistance is greater than 1 ohm, test the low speed GMLAN serial data circuit for an open or high resistance.

9. If all circuits are OK, replace the controller with communication problems.

• The voltage in the system is 9 - 16 V.
• The vehicle power mode master device requires serial data exchange to operate.

• The current fault code is cleared once the fault has disappeared.
• The fault code is cleared from the history when the ignition cycle counter in the controller reaches the reset threshold of 50 without the fault recurring.

• Using the above list of fault code definitions, determine which controller is experiencing communication problems.
• If there are multiple controllers with communication problems, select the one closest to the diagnostic connector (DLC).
• Using the communication line list, determine whether the GMLAN serial communication line used on the controller is high speed or low speed.
• Some controllers do not have internal protection for certain voltage outputs and may cause the battery positive voltage fuse or ignition voltage supply to blow. If the input voltage fuse is blown but no short circuit is detected in that circuit, make sure there are no shorted to ground voltage output circuits on the controllers before replacing the controller.
• This diagnostic can be used on any module that is required to communicate over the high or low speed GMLAN serial data line, provided the vehicle is equipped with an option that uses that module.

1. Use the above list of fault code definitions and diagnostic recommendations to determine which controller with the communication problem needs to be tested.
2. Turn off the ignition, disconnect the wiring harness connector on the controller where the connection is broken.

Important: Only high speed GMLAN controllers have a serial communications enable circuit OR an auxiliary serial communications wake-up circuit. Refer to the controller schematics to determine which controllers have these circuits. If the controller with the communication problem is missing one of these circuits, go to step 4.

3. Turn ignition ON, verify that the test lamp illuminates between the serial data line enable circuit OR the auxiliary serial data line wake-up circuit and ground.
• If the test lamp does not light, repair the open or high resistance in the circuit. If there are no faults in the circuits, replace the BCM.

4. Turn on the ignition, check if the test lamp lights between all positive battery voltage circuits and ground.
• If the test lamp does not light, eliminate the short to ground or open/high resistance in the circuit. If the circuit fuse is blown, also check the positive voltage outputs on the controller for a short to ground. If the circuits are OK, replace the faulty controller.

5. Check if the test lamp lights between all ignition voltage circuits and ground.
• If the test lamp does not light, eliminate the short to ground or open/high resistance in the circuit. If the circuit fuse is blown, also check the positive voltage outputs on the controller for a short to ground. If the circuits are OK, replace the faulty controller.

6. Check that the resistance between the controller ground circuits and the ground is no higher than 1 Ohm.
• If it is higher than 1 Ohm, repair the open circuit in the ground circuit.

7. Using the communication line list, determine if the controller with the communication problem is using a low speed GMLAN serial communication line.
• If the controller uses only high speed GMLAN communication line, replace the controller.

8. Verify that the resistance in the low speed GMLAN serial data line between the controller with the communication problem and the controller setting the fault code is less than 1 ohm.
• If the resistance is greater than 1 ohm, test the low speed GMLAN serial data circuit for an open or high resistance.

9. If all circuits are OK, replace the controller with communication problems.

• The controller detects that the system voltage is below a calibrated value, typically 7.8 V.
• The above condition is maintained for at least 1 second.

• The controller detects that the system voltage is higher than a calibrated value, typically 18 V.
• The above condition is maintained for at least 1 second.

• The controller immediately turns off all outputs when a voltage out of tolerance is detected, except for GMLAN and the Run/Start relay, which turn off after a 3-minute delay.
• The generation of other fault codes is blocked.

• The current fault code is cleared once the fault has disappeared.
• The fault code is cleared from the history when the ignition cycle counter in the controller reaches the reset threshold without the fault recurring.

• Once the resistance is out of range, the code will remain current until the resistance is below 0.28 ohms for 1 second.

• Once the resistance is out of range, the code will remain current until the resistance is above 36.1 kOhm for 1 second.

• The fault code will be transferred to the log if the heating, ventilation and air conditioning (HVAC) controller no longer detects the conditions for issuing this fault code.
• The current fault code is cleared once the fault has disappeared.

3. At this stage, the correct operation of the circuit in the upper voltage range is checked.
4. This step checks the circuit for proper operation in the lower voltage range. If the fuse on the jumper blows during this test, the signal circuit is shorted to the supply voltage.