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.

Refer to Exterior Lighting Systems Description and Operation in Lighting Systems, in order to avoid a misdiagnosis.
For an intermittent, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

DTC P0571 (6.6L)

Step	Action	Yes	No
Schematic Reference: Cruise Control Schematics Connector End View Reference: Cruise Control Connector End Views or Lighting Systems Connector End Views in Lighting Systems
1	Did you perform the Cruise Control Diagnostic System Check?	Go to Step 2	Go to Diagnostic System Check - Cruise Control
2	Turn OFF the ignition. Disconnect the stop lamp switch. Turn ON the ignition, with the engine OFF. Connect a test lamp between the stop lamp switch signal circuit and a good ground. Does the test lamp illuminate?	Go to Step 3	Go to Step 4
3	Test the stop lamp switch signal circuit for a short to voltage. Refer Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 9	Go to Step 6
4	Test the torque converter clutch (TCC) brake switch/cruise control release signal circuit for an open or for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 9	Go to Step 5
5	Inspect for poor connections at the harness connector of the stop lamp switch. 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 9	Go to Step 7
6	Inspect for poor connections at the harness connector of the engine control module (ECM). 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 9	Go to Step 8
7	Replace the stop lamp switch. Refer to Stop Lamp Switch Replacement in Lighting Systems. Did you complete the repair?	Go to Step 9	-
8	IMPORTANT: Program the replacement ECM. Replace the ECM. Refer to Engine Control Module (ECM) Replacement in Engine Controls - 6.6L (LB7) or Engine Control Module (ECM) Replacement in Engine Controls - 6.6L (LLY).Did you complete the replacement?	Go to Step 9	-
9	Use a 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