Test Description

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.

The number below refers to the step number on the diagnostic table.

2: This step determines if the condition is with the MIL control circuit or the PCM.

Malfunction Indicator Lamp (MIL) Always On

Step	Action	Yes	No
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module (ECM) Connector End Views or Engine Controls Connector End Views
1	Did you perform the Diagnostic System Check-Engine Controls?	Go to Step 2	Go to Diagnostic System Check - Engine Controls
2	Turn OFF the ignition. Disconnect the ECM. Turn ON the ignition, with the engine OFF. Observe the MIL. Is the MIL illuminated?	Go to Step 3	Go to Step 5
3	Remove the instrument panel cluster (IPC). Refer to Instrument Panel Cluster (IPC) Replacement in Instrument Panel, Gages, and Console. Test the MIL control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 6	Go to Step 4
4	Replace the IPC. Refer to Instrument Panel Cluster (IPC) Replacement in Instrument Panel, Gages, and Console. Did you complete the replacement?	Go to Step 6	-
5	Replace the ECM. Refer to Engine Control Module (ECM) Replacement . Did you complete the replacement?	Go to Step 6	-
6	Turn the ignition OFF for 30 seconds. Start the engine. Does the vehicle operate correctly without any MIL illumination, and without any stored DTCs?	System OK	Go to Diagnostic System Check - Engine Controls