P0571 Brake Switch 1 Performance

P0571 Code - the Powertrain Control Module (PCM) monitors the vehicle braking using the stop/brake lamp switch. For accuracy, the PCM monitors two separate brake switch signals. The operating mode of these signals are as follows:

P0571


Brake Signal 1 operation: The PCM sends out a 12 volt, low amperage signal, which may not illuminate a test light, on the brake signal 1 circuit. The PCM monitors the voltage on this circuit to indicate if the brake pedal is depressed or released. The brake signal 1 is normally closed through the stop/brake lamp switch. When the brake pedal is released, the brake signal 1 circuit is connected to ground circuit and the PCM reads 0.0 volts on the brake signal 1 circuit. When the pedal is pressed, the path to ground is opened and the PCM reads 12 volts on the brake signal 1 circuit.

Brake Signal 1 operation: 12 volts are sent on the ignition switch start/run circuit through the stop/brake lamp switch to the PCM on the Brake signal 2 circuit. The PCM monitors the voltage on this circuit to indicate if the brake pedal is depressed or released. No voltage on the Brake signal 2 circuit indicates to the PCM that the pedal is pressed, and 12.0 volts indicates that the brake pedal is released.
Default actions, the Powertrain Control Module (PCM) receives a Brake switch 2 PRESSED signal without receiving a Brake switch 1 PRESSED signal for 0.5 seconds. Default actions, MIL light illuminte and cruise control will not work for the rest of the key cycle.

Possible causes P0571 Code

  • Fused ignition switch output circuit open or shorted to ground
  • Fused B+ circuit open or shorted to ground
  • Brake switch 1 signal circuit open
  • Brake switch 1 signal circuit shorted to ground
  • Brake switch 2 signal circuit open
  • Brake switch 2 signal circuit shorted to ground
  • Brake switch
  • Powertrain Control Module (PCM)

Diagnose P0571 Code


Step 1. Check for an active DTC
Make sure the brake switch is properly adjusted before continuing. Turn the ignition on, with the scan tool read DTCs and record on the repair order. Press and release the brake pedal.

Is the DTC active or pending?

Yes, go to step 2.
No, perform the PCM intermittent condition.

Step 2. Check the fused ignition switch output circuit for an open
Turn the ignition off, disconnect the brake switch harness connector. Turn the ignition on, measure the voltage on the fused ignition switch output circuit at the Brake switch harness connector.

Is the voltage equal to Battery voltage?

Yes, go to step 3.
No, repair the fused ignition switch output circuit for an open. If the fuse is blown, check the fused ignition switch output circuit and brake switch 1 signal circuit for a short to ground.

Step 3. Check the fused B+ circuit for an open
Measure the voltage on the fused B+ circuit at the Brake switch harness connector.

Is the voltage equal to Battery voltage?

Yes, go to step 4.
No, repair the fused B+ circuit for an open. If thee fuse is blown, check the fused B+ circuit and brake switch 2 signal circuit for a short to ground.

Step 4. Brake switch
Reconnect the Brake switch harness connector. Back probe and measure between ground and the brake switch 1 signal circuit at the brake switch harness connector with the brake pedal PRESSED. Back probe and measure between ground and the brake switch 2 signal circuit at the brake switch harness connector with the brake pedal NOT PRESSED

Is the voltage reading equal to Battery voltage for both of the measurements taken?

Yes, go to step 5.
No, verify that there is good pin to terminal contact in the switch and Powertrain Control Module harness connectors. If no problems are found, replace the brake switch.

Step 5. Check the brake switch 1 signal circuit for a short to ground
Turn the ignition off, disconnect the brake switch harness connector. Disconnect the PCM harness connector, check for continuity between ground and the brake switch 1 signal circuit at the brake switch harness connector.

Is there continuity between ground and the Brake switch 1 signal circuit?

Yes, repair the brake switch 1 signal circuit for a short to ground.
No, go to step 6.

Step 6. Check the brake switch 2 signal circuit for a short to ground
Check for continuity between ground and the brake switch 2 signal circuit at the brake switch harness connector.

Is there continuity between ground and the brake switch 2 signal circuit?

Yes, repair the brake switch 2 signal circuit for a short to ground.
No, go to step 7.

Step 7. Check the brake switch 1 signal circuit for an open/high resistance
Meeasure the resistance of the brake switch 1 signal circuit between the brake switch harness connector and the PCM harness connector.

Is the resistance below 3.0 Ohms?

Yes, go to step 8.
No, repair the brake switch 1 signal circuit for an open or high resistance.

Step 8. Check the Brake switch 2 signal for an open/high resistance
Measure the resistance of the brake switch 2 signal circuit between the brake switch harness connector and the PCM harness connector.

Is the resistance below 3.0 Ohms?

Yes, go to step 9.
No, repair the brake switch 2 signal circuit for an open or high resistance.

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