2012 Jeep Wrangler JK Factory Service Manual 28 - DTC-Based Diagnostics

P0571-BRAKE SWITCH 1 PERFORMANCE

P0571-BRAKE SWITCH 1 PERFORMANCE

For a complete wiring diagram, refer to the Wiring Information.


The Powertrain Control Module (PCM) monitors the vehicle braking via the Stop Lamp Switch. For accuracy, the PCM monitors two separate brake switch signals. The operating mode of these signals are as follows:

Brake Switch Signal 1 operation: The PCM sends out a 12 Volt, low amperage signal, which may not illuminate a test light, on the (B15) Brake Switch 1 circuit. The PCM monitors the voltage on this circuit to indicate if the brake pedal is depressed or released. When the brake pedal is released, the (B15) Brake Switch 1 circuit is connected to the (Z914) ground circuit and the PCM reads Zero Volts on the (B15) Brake Switch 1 circuit. When the pedal is pressed, the path to ground is broken and the PCM reads 12 Volts on the (B15) Brake Switch 1 circuit.

Brake Switch Signal 2 operation: 12 Volts are sent on the (F941) Ignition Switch Start/Run circuit through the Stop Lamp Switch to the PCM on the (B16) Brake Switch 2 circuit. The PCM monitors the voltage on this circuit to indicate if the brake pedal is depressed or released. Zero Volts on the (B16) Brake Switch 2 circuit indicates to the PCM that the pedal is pressed, and 12 Volts indicate that the brake pedal is released.


Possible Causes

(B15) BRAKE SWITCH 1 SIGNAL CIRCUIT SHORTED TO GROUND
(B15) BRAKE SWITCH 1 SIGNAL CIRCUIT OPEN
(Z914) GROUND CIRCUIT OPEN
(F941) IGNITION SWITCH START/RUN CIRCUIT OPEN
(B16) BRAKE SWITCH 2 SIGNAL CIRCUIT SHORTED TO VOLTAGE
(B16) BRAKE SWITCH 2 SIGNAL CIRCUIT OPEN
STOP LAMP SWITCH
POWERTRAIN CONTROL MODULE

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).


1. CHECK THE BRAKE SWITCH 1 STATUS

1. Turn the ignition on.
2. While observing the BRAKE SWITCH 1 status on the scan tool display, press and release the brake pedal several times.


Does the scan tool display BRAKE SWITCH 1: PRESSED and NOT PRESSED for the appropriate pedal position?

Yes


No


2. CHECK THE BRAKE SWITCH 2 STATUS

1. While observing the BRAKE SWITCH 2 status on the scan tool display, press and release the brake pedal several times.


Does the scan tool display BRAKE SWITCH 2: PRESSED and NOT PRESSED for the appropriate pedal position

Yes


No


3. INTERMITTENT CONDITION



NOTE: The conditions that set the DTC are not present at this time. The following list may help in identifying the intermittent condition.
1. With the engine running at normal operating temperature, monitor the scan tool parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set.
2. Review the DTC When Monitored and Set Conditions. If possible, try to duplicate the conditions under which the DTC was set.
3. Perform any Technical Service Bulletins (TSB) that may apply.
4. Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires.
5. Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals.


Were any of the above conditions present?

Yes


No


4. CHECK THE (F941) IGNITION SWITCH START/RUN CIRCUIT FOR AN OPEN
1. Turn the ignition off.
2. Disconnect the Brake Lamp Switch harness connector.
3. Turn the ignition on.
4. Using a 12-volt test light connected to ground, probe the (F941) Ignition Switch Start/Run circuit at the Brake Lamp Switch harness connector.


NOTE: The test light should be illuminated and bright.


Is the test light illuminated and bright?

Yes


No


5. CHECK THE (B16) BRAKE SWITCH 2 SIGNAL CIRCUIT FOR A SHORT TO VOLTAGE
1. Measure the voltage on the (B16) Brake Switch Signal 2 circuit at the Stop Lamp Switch harness connector.


Is there any voltage present?

Yes


No


6. CHECK THE (B16) BRAKE SWITCH 2 SIGNAL CIRCUIT FOR AN OPEN/HIGH RESISTANCE
1. Turn the ignition off.
2. Disconnect the PCM C2 harness connector.
3. Measure the resistance of the (B16) Brake Switch 2 Signal circuit between the Brake Lamp Switch harness connector and the PCM C2 harness connector.


Is the resistance below 5.0 Ohms?

Yes


No


7. CHECK THE BRAKE LAMP SWITCH

1. Reconnect the Brake Lamp Switch harness connector.
2. Turn the ignition on.
3. Using a 12-Volt test light connected to ground, backprobe the (B16) Brake Switch Signal 2 circuit at the Stop Lamp Switch harness connector with the brake pedal NOT depressed


NOTE: The test light should be illuminated and bright.


Is the test light illuminated and bright?

Yes


No


8. CHECK THE (Z914) GROUND CIRCUIT FOR AN OPEN/HIGH RESISTANCE
1. Turn the ignition off.
2. Disconnect the Brake Lamp Switch harness connector.
3. Measure the resistance between ground and the (Z914) Ground circuit at the Brake Lamp Switch harness connector.


Is the resistance below 5.0 Ohms?

Yes


No


9. CHECK THE (B15) BRAKE SWITCH 1 SIGNAL CIRCUIT VOLTAGE
1. Turn the ignition on.
2. Measure the voltage on the (B15) Brake Switch Signal 1 circuit at the Brake Lamp Switch harness connector.


Is the voltage reading approximately 12.0 Volts?

Yes


No


10. CHECK THE (B15) BRAKE SWITCH 1 SIGNAL CIRCUIT FOR A SHORT TO GROUND
1. Turn the ignition off.
2. Disconnect the PCM C2 harness connector.
3. Measure the resistance between ground and the (B15) Brake Switch 1 Signal circuit at the Brake Lamp Switch harness connector.


Is the resistance above 10K Ohms?

Yes


No


11. CHECK THE (B15) BRAKE SWITCH 1 SIGNAL CIRCUIT FOR AN OPEN/HIGH RESISTANCE
1. Measure the resistance of the (B15) Brake Switch 1 Signal circuit between the Brake Lamp Switch harness connector and the PCM C2 harness connector.


Is the resistance below 5.0 Ohms?

Yes


No