Diagnostic Aids

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

IMPORTANT: The scan tool communication with the modules connected only to high speed GMLAN data link requires the use of the CANdi module. Due to configuration of this vehicle, they may be communication DTCs set against modules that are able to communicate with the scan tool.

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

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 ON the ignition, with the engine OFF. Retrieve DTCs from the powertrain control module (PCM). Did you record any DTCs in the range of U1881-U1899?	Go to DTC U1881-U1899	Go to Step 3
3	Did you record any DTCs in the range of U0100-U0299?	Go to DTC U0100-U0299 (Diesel Engine) DTC U0100-U0299 (HP2)	Go to Step 4
4	Attempt to communicate with the following modules: The energy storage control module (ESCM) The starter/generator control module (SGCM) The electro-hydraulic power steering (EHPS) module Does the scan tool communicate with all listed modules?	Go to Step 5	Go to Step 6
5	IMPORTANT: Turn ON the ignition, with the engine OFF, when testing for a short to voltage. Use the DMM MIN/MAX function to capture intermittent conditions. Disconnect the scan tool from the data link connector (DLC). Test the high speed GMLAN serial data circuits for the following conditions: An intermittent short to ground An intermittent short to voltage An intermittent short between high speed GMLAN (+) and (-) circuits An intermittent open on any of the circuits Refer to the following in Wiring Systems: Testing for Intermittent Conditions and Poor Connections Circuit Testing Connector Repairs Wiring Repairs Did you find and correct the condition?	Go to Step 12	Go to Diagnostic Aids
6	Turn OFF the ignition. Disconnect the scan tool from the data link connector (DLC). Inspect for poor connections at the DLC terminals 6 and 14. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 8	Go to Step 7
7	Disconnect the SGCM. Repair the high speed GMLAN serial data circuits between DLC connector and SGCM for an open. Refer to Wiring Repairs and Connector Repairs in Wiring Systems. Did you complete the repair?	Go to Step 8	-
8	Reconnect all of the disconnected modules. Install a scan tool. Turn ON the ignition, with the engine OFF. Select the Display DTCs function for each module. Record all of the displayed DTCs and the DTC status. Did you record any DTCs which begin with a "U" and with a current status?	Go to Diagnostic Trouble Code (DTC) List	Go to Step 9
9	Did you record any DTCs which do not begin with a "U"?	Go to Step 10	Go to Step 11
10	Diagnose the DTCs as directed by the diagnostic procedures for the particular module or concern. Did you complete the action?	Go to Step 11	-
11	Did you diagnose all of the DTCs?	Go to Step 12	Go to Step 9
12	Use the scan tool in order to clear the DTCs. Did you complete the action?	System OK	-