For 1990-2009 cars

### Circuit Description

The stop lamp switch signal circuit is a direct hardware input to the Engine Control Module (ECM) from the Instrument Panel Module (IPM). The ECM monitors the stop lamp switch signal circuit in order to detect when the brake pedal has been applied. When the brake pedal is pressed, the IPM sends a Class 2 serial data message to the ECM indicating that the brake pedal has been applied. The IPM also sends a high voltage signal on the stop lamp switch signal circuit to the ECM. This DTC will set if the Class 2 serial data message and the high voltage signal on the stop lamp switch signal circuit do not match.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0571 Brake Switch Circuit 1

### Conditions for Running the DTC

• | There are no vehicle speed sensor DTCs set.

| OR

• | The reference voltage is less than 4.9 volts.

• | DTC P0571 runs continuously once the above conditions are met for more than 2 seconds.

### Conditions for Setting the DTC

• | The ECM detects that the Class 2 serial data message from the IPM and the voltage signal on the stop lamp switch signal circuit do not match for 10 consecutive times that this diagnostic is run.

| or

• | The signal voltage value is not within the specified range.

• | The above conditions last for 50 seconds.

### Action Taken When the DTC Sets

• | Turn OFF the cruise control system.

• | When the diagnostic runs and fails, the ECM stores the DTC information into the memory.

• | The Malfunction Indicator Lamp (MIL) does not illuminate.

• | The ECM will record the operating conditions at the time the diagnostic failed. The ECM stores this information in Failure Records.

### Conditions for Clearing the DTC

• | A last test failed, or the current DTC, clears when the diagnostic runs and does not fail.

• | A history DTC clears after 40 consecutive warm-up cycles, if the failures are not reported by this or any other emission related diagnostic.

• | Clear the MIL/DTC with a scan tool.

### Diagnostic Aids

In order to avoid a misdiagnosis, inspect for proper operation of the stop lamps. Refer to Exterior Lighting Systems Description and Operation .

For an intermittent condition, refer to Testing for Intermittent Conditions and Poor Connections .

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Cruise Control Schematics Connector End View Reference: Engine Control Module Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Do the stop lamps operate properly? | Go to Step 3 | Go to Stop Lamps Inoperative or Stop Lamps Always On
3 |

1. Install the scan tool.
2. Turn ON the ignition, with the engine OFF.
3. With a scan tool, observe the Stop Lamp Pedal switch parameter in the engine control module (ECM) Cruise/Traction data list.
4. Press the brake pedal.

Does the Stop Lamp Pedal Switch parameter display Applied?

Go to Step 5

Go to Step 4

4 | Test the stop lamp switch signal circuit for an open or for a high resistance between the electronic brake control module (EBCM) and the ECM. Refer to Circuit Testing and Wiring Repairs . Do you find and correct the condition? | Go to Step 9 | Go to Step 6
5 | Inspect for poor connections at the harness connector of the electronic brake control module (EBCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Do 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 ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Do you find and correct the condition? | Go to Step 9 | Go to Step 8
7 | Replace the IPM. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | Go to Step 9 | --
8 | Replace the ECM. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | Go to Step 9 | --
9 |

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Conditions for Running the DTC.

Does the DTC reset?

Go to Step 2

System OK