Circuit/System Testing

1. Attempt to communicate with all control modules on the Powertrain high speed GMLAN serial data circuit. Refer to Data Link References . Communications should not be available with two or more control modules on the Powertrain high speed GMLAN serial data circuit.
   • If only one control module is not communicating, diagnose that control module only. Refer to DTC U0100-U02FF (except U029D and U029E) , DTC U0100-U02FF (U029D and U029E only) .
2. Ignition OFF, disconnect the harness connectors with the Powertrain high speed GMLAN serial data circuits at an easily accessible control module that is not communicating.
3. Ignition ON, test for less than 4.5 V between each Powertrain high speed GMLAN serial data circuit at the control module that was just disconnected and ground.
   • If one or more Powertrain high speed GMLAN serial data circuits are greater than the specified range, test the Powertrain high speed GMLAN serial data circuit for a short to voltage. Refer to Testing the Serial Data Circuits for a Short to Voltage.
4. Ignition OFF, key out of the ignition switch, all access doors closed, wait 1 minute, test for greater than 100 Ω between each Powertrain high speed GMLAN serial data circuit at the control module connector that was just disconnected and ground.
   • If one or more Powertrain high speed GMLAN serial data circuits are less than the specified value, test the Powertrain high speed GMLAN serial data circuit for a short to ground. Refer to Testing the Serial Data Circuits for a Short to Ground.
5. Test for 110-130 Ω between the Powertrain high speed GMLAN serial data circuits at the control module that was just disconnected.
   • If less than 110 Ω, test for a short between the Powertrain high speed GMLAN serial data circuits. Refer to Testing the Serial Data Circuits for a Short Between The Circuits.
   • If greater than 130 Ω but less than infinite, test the Powertrain high speed GMLAN serial data circuit for an open/high resistance. Refer to Testing the Serial Data Circuits for an Open/High Resistance.
6. Refer to Testing the Control Module Circuits.
7. If all circuits test normal, replace the control module that was just disconnected.

Testing the Serial Data Circuits for a Short to Voltage

1. Ignition OFF, disconnect the harness connectors with the Powertrain high speed GMLAN serial data circuits at another control module that is not communicating, in the direction of the circuit shorted to voltage.
2. Ignition ON, test for greater than 4.5 V between each Powertrain high speed GMLAN serial data circuit at the control module connector that was just disconnected and ground. Verify that one or more Powertrain high speed GMLAN serial data circuits are greater than 4.5 V.
   • If all Powertrain high speed GMLAN serial data circuits are less than the specified range, replace the control module that was just disconnected.
3. Repeat step 1 until one of the follow conditions are isolated:
   • A short to voltage on the Powertrain high speed GMLAN serial data circuit between 2 control modules or splice packs, if equipped.
   • A short to voltage on the Powertrain high speed GMLAN serial data circuit between a control module and a terminating resistor.

Testing the Serial Data Circuits for a Short to Ground

1. Ignition OFF, disconnect the harness connectors with the Powertrain high speed GMLAN serial data circuits at another control module that is not communicating, in the direction of the circuit shorted to ground.
2. Ignition OFF for 60 seconds, test for less than 1k Ω between each Powertrain high speed GMLAN serial data circuit at the control module connector that was just disconnected and ground. Verify that one or more Powertrain high speed GMLAN serial data circuits are less than 1k Ω.
   • If all Powertrain high speed GMLAN serial data circuits are greater than the specified range, replace the control module that was just disconnected.
3. Repeat step 1 until one of the follow conditions are isolated:
   • A short to ground on the Powertrain high speed GMLAN serial data circuit between 2 control modules or splice packs, if equipped.
   • A short to ground on the Powertrain high speed GMLAN serial data circuit between a control module and a terminating resistor.

Testing the Serial Data Circuits for a Short Between The Circuits

1. Connect the harness connectors at the control module that was previously disconnected.
2. Ignition OFF, disconnect the harness connectors with the Powertrain high speed GMLAN serial data circuits at another control module that is not communicating, in the direction of the circuits shorted together.
3. Ignition OFF for 60 seconds, test for less than 110 Ω between each pair of Powertrain high speed GMLAN serial data circuits at the control module connector that was just disconnected. Verify that one pair of Powertrain high speed GMLAN serial data circuits are less than 110 Ω.
   • If each pair of Powertrain high speed GMLAN serial data circuits is greater than the specified range, replace the control module that was just disconnected.
4. Repeat step 1 until one of the following conditions are isolated:
   • Powertrain high speed GMLAN serial data circuits shorted together between 2 control modules or splice packs, if equipped
   • Powertrain high speed GMLAN serial data circuits shorted together between a control module and a terminating resistor
   • A shorted terminating resistor

Testing the Serial Data Circuits for an Open/High Resistance

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

Testing the Control Module Circuits

1. Ignition OFF for 60 seconds, test for less than 10 Ω between each ground circuit terminal at the control module that was just disconnected and ground.
   • If greater than the specified range, test the ground circuit for an open/high resistance.
2. If equipped, ignition ON, verify that a test lamp illuminates between each B+ circuit terminal and ground.
   • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the control module for a short to ground. If the circuits test normal, replace the appropriate control module.
3. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.
   • If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the control module for a short to ground. If the circuits test normal, replace the appropriate control module.