Diagnostic Aids

WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

The engine will not start when there is a total malfunction of the GMLAN serial data circuits while the engine is not running. The following conditions may cause a total loss of GMLAN data communication:

Any of the GMLAN High Speed serial data circuits shorted to ground.
Any of the GMLAN High Speed serial data circuits shorted to voltage.
A short between GMLAN High Speed serial data circuits.
An internal malfunction of a module on the GMLAN network that causes a short to voltage or ground.

Scan Tool Does Not Communicate with High Speed GMLAN Device

Step	Action	Yes	No
Schematic Reference: Data Link Connector (DLC) Schematics Connector End View Reference: Master Electrical Component List in Wiring Systems
1	Does the scan tool power up?	Go to Step 2	Go to Scan Tool Does Not Power Up
2	Turn the ignition ON, with the engine OFF. Attempt to communicate with each module on the GMLAN serial data circuit using a scan tool with a CANdi adaptor in-line module properly installed. Does the scan tool communicate with all modules on the GMLAN serial data circuits?	Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems	Go to Step 3
3	Disconnect the scan tool from the data link connector (DLC). Turn the ignition OFF. Disconnect all non-communicating modules on the high speed GMLAN serial data circuit. Turn the ignition ON, with the engine OFF. Test the high speed GMLAN serial data circuit between the DLC and all the modules on the high speed GMLAN serial data circuit, for the following conditions: An open A short to ground A short to voltage Refer to the following: Control Module References in Body Control System for the applicable schematic Circuit Testing in Wiring Systems Wiring Repairs in Wiring Systems Did you find and correct the condition?	Go to Step 7	Go to Step 4
4	Test the following circuits of the module that is not communicating for an open or high resistance: The battery positive voltage input circuits The battery voltage output circuits The ignition voltage input circuits The ignition voltage output circuits The switched battery positive voltage supply circuits The ground circuits Refer to the following: Control Module References in Body Control System for the applicable schematic Circuit Testing in Wiring Systems Wiring Repairs in Wiring Systems Did you find and correct the condition?	Go to Step 7	Go to Step 5
5	Inspect for poor connections and terminal tension at the following harness connector circuits of the module that is not communicating: The battery positive voltage input circuits The battery positive voltage output circuits The ignition voltage input circuits The ignition voltage output circuits The switched battery positive voltage supply circuits The ground circuits The high speed GMLAN serial data circuits Refer to the following: Control Module References in Body Control System for the applicable schematic Testing for Intermittent Conditions and Poor Connections in Wiring Systems Connector Repairs in Wiring Systems Did you find and correct the condition?	Go to Step 7	Go to Step 6
6	IMPORTANT: Perform the programming or setup procedure for the replaced control module, if required. Replace the module that is not communicating on the high speed GMLAN serial data circuit. Refer to Control Module References in Body Control System for the applicable replacement procedure.Did you complete the replacement?	Go to Step 7	-
7	Connect all modules and connectors. Connect the scan tool to the DLC. Turn the ignition ON, with the engine OFF. Perform the Diagnostic System Check for the system exhibiting symptoms. Refer to Control Module References in Body Control System. Did you complete the operation?	System OK	Go to Step 2