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 numbers below refer to the step numbers on the diagnostic table.

2: During the SGCM cooling fan relay operation, listen for an audible click. Command the ON and the OFF states. Repeat the commands as necessary.
3: Verifies that the SGCM is providing voltage to the SGCM cooling fan relay.
4: Tests for an open in the ground circuit to the SGCM cooling fan relay.
5: Tests for constant voltage to the SGCM cooling fan relay.

DTC P1AC1 or P1AC2

Step	Action	Yes	No
Schematic Reference: Engine Cooling Schematics Connector End View Reference: Cooling System Connector End Views
1	Did you perform the Engine Cooling Diagnostic System Check?	Go to Step 2	Go to Diagnostic System Check - Engine Cooling
2	Install a scan tool. Turn ON the ignition, with the engine OFF. With a scan tool, command the SGCM Fan Speed ON and OFF. Does the SGCM cooling fan relay turn ON and OFF with each command?	Go to Diagnostic Aids	Go to Step 3
3	Turn OFF the ignition. Disconnect the starter/generator control module (SGCM) cooling fan relay. Turn ON the ignition, with the engine OFF. Connect a test lamp to ground. Probe the control circuit of the SGCM cooling fan relay with a test lamp that is connected to battery positive voltage. With a scan tool, command the SGCM Fan Speed ON and OFF. Does the test lamp turn ON and OFF with each command?	Go to Step 4	Go to Step 5
4	Connect a test lamp between the control circuit of the SGCM cooling fan relay and the ground circuit of the SGCM cooling fan relay. With a scan tool, command the SGCM Fan Speed ON and OFF. Does the test lamp turn ON and OFF with each command?	Go to Step 8	Go to Step 10
5	Does the test lamp remain illuminated with each command?	Go to Step 7	Go to Step 6
6	Test the control circuit of the SGCM cooling fan relay for a short to ground and an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 13	Go to Step 9
7	Test the control circuit of the SGCM cooling fan relay for a short to voltage. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 13	Go to Step 9
8	Inspect for poor connections at the SGCM cooling fan relay. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 13	Go to Step 11
9	Inspect for poor connections at the harness connector of the SGCM. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 13	Go to Step 12
10	Repair the ground circuit of the SGCM cooling fan relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair?	Go to Step 13	-
11	Replace the SGCM cooling fan relay. Refer to Relay Replacement (Within an Electrical Center) or Relay Replacement (Attached to Wire Harness) in Wiring Systems. Did you complete the replacement?	Go to Step 13	-
12	IMPORTANT: Perform the programming procedure for the SGCM. Replace the SGCM. Refer to Starter/Generator Control Module (SGCM) Replacement (5.3L Engine w/RPO HP2) in Engine Electrical.Did you complete the replacement?	Go to Step 13	-
13	Use the scan tool in order to clear the DTCs. Operate the vehicle within the Conditions for Running the DTC. Does the DTC reset?	Go to Step 2	System OK