Circuit/System Verification
NOTE:
Each control module may need to be disconnected to isolate a circuit fault. Use the schematic to identify the following:
- Control modules the vehicle is equipped with
- High speed GMLAN serial data circuit terminating resistors
- Control module locations on the high speed GMLAN serial data circuits
- Each control module's high speed GMLAN serial data circuit terminals
- Attempt to communicate with all control modules on the high speed GMLAN serial data circuit. Refer to Data Link References . Communications should not be available with two or more control modules on the high speed GMLAN serial data circuit.
- If only one control module is not communicating, diagnose that control module only. Refer to DTC U0100-U02FF (without HP6) , DTC U0100-U02FF (with HP6) .
- Disconnect the scan tool from the data link connector (DLC). The following tests will be done at the DLC connector.
- Ignition OFF and all vehicle systems OFF, key out of the ignition switch, all access doors closed. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 10 Ω between the ground circuit terminal 5 and ground.
- If greater than the specified range, test the ground circuit for an open/high resistance.
- Ignition ON, test for less than 4.5 V between the serial data circuits listed below and ground:
- Terminal 6
- Terminal 14
- If greater than the specified range, test the serial data circuit for a short to voltage. Refer to Testing the Serial Data Circuits for a Short to Voltage.
- Ignition OFF and all vehicle systems OFF, key out of the ignition switch, all access doors closed. It may take up to 2 minutes for all vehicle systems to power down. Test for greater than 100 Ω between the serial data circuits listed below and ground:
- Terminal 6
- Terminal 14
- If less than the specified range, test the serial data circuit for a short to ground. Refer to Testing the Serial Data Circuits for a Short to ground.
- Test for 50-70 Ω between the serial data circuits terminal 6 and terminal 14.
- If less than 35 Ω, test for a short between the serial data circuits. Refer to Testing the Serial Data Circuits for a Short between the Circuits.
- If 35-50 Ω there may be a third terminating resistor between the serial data circuits. This can happen if the incorrect control module is installed. Some control modules are available with and without the terminating resistors installed to reduce the need of terminating resistors in the wiring harness.
- If greater than 70 Ω but less than infinite, test the serial data circuit for an open/high resistance. Refer to Testing the Serial Data Circuits for an Open/High Resistance.
- If infinite, refer to Testing the DLC Serial Data Circuits for an Open.