Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
High Speed GMLAN Serial Data Bus (+) | 1 | 2 | 1 | -- |
High Speed GMLAN Serial Data Bus (-) | 1 | 2 | 1 | -- |
1. No communication on any high speed GMLAN module. 2. An open in only one high speed GMLAN serial data circuit may allow degraded communication between the modules or no communication with a specific module. | ||||
Circuit/System Description
Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The high speed GMLAN serial data bus uses two 120 ohm terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits. One of the resistors is connected near the data link connector (DLC) end of the link and the other is internal to the ECM/PCM end of the link. The DLC terminating resistor is not internal to a module. Modules connected to the high speed GMLAN serial data circuits are the transmission control module (TCM), glow plug control module (GPCM), and the engine control module/powertrain control module (ECM/PCM).
Diagnostic Aids
| • | Use the Step Replacement to identify the high speed GMLAN serial data modules. |
| • | This test is used for a total high speed GMLAN communication failure. If only 1 module is not communicating and sets no DTC, ensure that the vehicle is equipped with the module, then use DTC U0100-U0299 for diagnostics. |
| • | Use the DMM MIN/MAX function to capture/locate intermittent conditions. |
| • | The following conditions may cause a total loss of high speed GMLAN data communication: |
| - | A short between high speed GMLAN (+) and high speed GMLAN (-) circuits |
| - | Any of the high speed GMLAN serial data circuits shorted to ground or voltage |
| - | A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits |
Reference Information
Schematic Reference
Connector End View Reference
Master Electrical Component List
Electrical Information Reference
Circuit/System Testing
- Ignition OFF, disconnect the harness connector of the GPCM.
- Ignition ON, with a scan tool attempt to communicate with the TCM. Communication should be possible.
- At the GPCM connector, test for less than 1.0 volt between the high speed GMLAN serial data circuits of the ECM/PCM and ground.
- At the GPCM connector, test for infinite resistance between the high speed GMLAN serial data circuit of the ECM/PCM and ground.
- Test for between 115-125 ohms of resistance between the high speed GMLAN serial data (+) and (-) circuits of the ECM/PCM.
- If the circuits test normal, replace the GPCM.
| ⇒ | If no communication, test the high speed GMLAN serial data (+) and (-) circuits between the DLC, TCM and 120 Ohm resistor for a short to ground, short to voltage, a short between them, and an open/high resistance, and between the TCM and GPCM for a short to ground, short to voltage, or a short between them. If the circuits test normal, replace the TCM. |
| ⇒ | If greater than 1.0 volt, test the serial data circuit for a short to voltage. If the circuits test normal, replace the ECM/PCM. |
| ⇒ | If less than infinite resistance, test the serial data circuit for a short to ground. If the circuits test normal, replace the ECM/PCM. |
| ⇒ | If less than the specified resistance, test the serial data circuits for a short between them. If the circuits test normal, replace the ECM/PCM. |
| ⇒ | If greater than the specified resistance, test the serial data circuits for an open/high resistance. If the circuits test normal, replace the ECM/PCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair.
| • | Control Module References for module replacement, setup, and programming |
