Scan Tool Does Not Communicate with High Speed GMLAN Device
Scan Tool Does Not Communicate with High Speed GMLAN Device
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* 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/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 engine control module/powertrain control module ECM/PCM end of the link.
Diagnostic Aids
* Use the Data Link References 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.
* 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
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector of the transmission control module (TCM).
2. Test for 108-132 ohms between the serial data circuit terminal 6 and terminal 7.
^ If less than the specified range, test the serial data circuits for a short between them. If the circuits test normal, replace the 120 ohm resistor.
^ If greater than the specified range, test the serial data circuits for open/high resistance. If the circuits test normal, replace the 120 ohm resistor.
3. Ignition ON, test for less than 1.0 volt between the serial data circuit terminal 6 and ground, and between terminal 7 and ground.
^ If greater than the specified range, test the serial data circuit for a short to voltage.
4. Test for infinite resistance between the serial data circuit terminal 6 and ground, and between terminal 7 and ground.
^ If less than the specified value, test the serial data circuit for a short to ground.
5. Test for 108-132 ohms between the serial data circuit terminal 37 and terminal 38.
^ If less than the specified range, test the serial data circuits for a short between them. If the circuits test normal, replace the ECM.
^ If greater than the specified range, test the serial data circuits for open/high resistance. If the circuits test normal, replace the ECM.
6. Ignition ON, test for less than 1.0 volt between the serial data circuit terminal 37 and ground, and between terminal 38 and ground.
^ If greater than the specified range, test the serial data circuit for a short to voltage. If the circuits test normal, replace the ECM.
7. Test for infinite resistance between the serial data circuit terminal 37 and ground, and between terminal 38 and ground.
^ If less than the specified value, test the serial data circuit for a short to ground. If the circuits test normal, replace the ECM.
8. If the circuits test normal, replace the TCM.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair. Verification Tests
* GMLAN Wiring Repairs