Fix P0571: Mechanic’s solutions that WORKED

The P0571: Cruise Control/Brake Switch A Circuit Malfunction points out a fault in the brake switch circuit. This issue is typically caused by problems with the brake switch itself or related wiring and control systems. Addressing this code is crucial for maintaining the proper function of the vehicle’s braking system.

P0571 quick overview

Description	P0571: Cruise Control/Brake Switch A Circuit Malfunction
Is it serious?	This code can be serious as it relates to the vehicle’s braking system, which is critical for safe driving.
Possible causes	– Faulty or misaligned brake switch – Damaged or disconnected wiring to the brake switch – Faulty ABS control module – Issues in the CAN bus communication network
How to diagnose?	Inspect Brake Switch: Check the brake switch for proper alignment and functionality. Examine Wiring: Look for any damage or disconnections in the wiring to the brake switch. Check ABS Control Module: Investigate any potential issues with the ABS control module. Evaluate CAN Bus System: Check the CAN bus communication network for faults or errors.

How to fix P0571 – learn from mechanics

I looked into P0571 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Dodge

Vehicle Information: 2008 Dodge Caliber SXT 2.0L

Issue + Repair History:

• Right rear wheel speed showed a constant speed in kmph, but occasionally dropped to zero.
• ABS had a C102B error code for RR wheel speed sensor circuit.
• PCM displayed U1418, indicating implausible RR wheel speed received.
• P0571 brake switch performance issue also noted.
• Previously replaced right rear bearing and sensor.

Other OBD2 Codes + Test Results:

• PCM: U1418, P0571
• ABS: C102B

Suggestions to Fix Issue:

• Check if the installed assembly and sensor are aftermarket; these components are very sensitive.
• Verify the 12V signal wire and ensure good voltage drop, plus check that the wires from the module to the sensor have no resistance.
• Use a low amp probe to check the waveform and ensure it’s pulsing correctly.
• Ensure the installed bearing is of high quality, as a defective bearing could be an issue.
• Consider the module as a last option.
• Use an oscilloscope directly on the wheel speed sensor (WSS) to monitor while driving.

Final Fix:

• Located and repaired wiring that was rubbing on a sharp body edge under the left front fender well. Also relocated the harness to prevent further issues.

Case #2: Saturn

Vehicle Information: 2000 Saturn LS2 3.0L

Issue + Repair History:

• Intermittent starting issues after running; restarting possible after a brief pause.
• Tail lights malfunction when headlights are on and brakes are applied.
• Two codes present: P0571 (cruise control brake switch circuit) and P1631 (theft deterrent fuel enable signal not correct).
• Tail lights issue noted under recall.

Other OBD2 Codes + Test Results:

• P1631: Theft deterrent fuel enable signal not correct
• P0571: Cruise control brake switch circuit

Suggestions to Fix Issue:

• Address the tail lamp issue as per recall instructions.
• For the starting problem, consider a passlock sensor issue, possibly needing a reflash for the BCM.
• Check the ignition cylinder housing for passlock sensor or wiring issues.
• Inspect the main fuse block for any melted connections, particularly at the rear.
• Verify the brake pedal input to the cruise module with a scan tool, and consider reflash of the PCM if necessary.
• Relearn the passlock sensor by turning the key on for 10 minutes, cycling it off and on for a few minutes, and repeating this process.
• Inspect for high resistance in the main harness or battery cables, especially in cases of acid leakage or flood damage.

Final Fix:

• Addressed the tail lights issue under the recall.
• Recycled the passlock by turning the key on for 10 minutes, then off and on for a few minutes, repeating this process to relearn the key code.

Case #3: Volkswagen

Vehicle Information: 2005 Volkswagen Jetta 2.5 2.5L

Issue + Repair History:

• Intermittent acceleration issue; car wouldn’t move despite pressing gas and RPMs rising.
• Initially recommended transmission service.
• Problem persisted; during a test drive, car didn’t move for about 5 seconds after shifting from N to D.
• No codes in transmission or engine module initially.
• EPC light came on during subsequent test drives, still no codes.
• Scanner showed computer cutting pedal signal to the throttle.
• Throttle body alignment procedure performed, but issue continued.
• Plan to test throttle body and pedal sensors next.

Other OBD2 Codes + Test Results:

• P0571: Brake pedal switch malfunction
• Initially, no codes were present, but eventually, P0571 was set.

Suggestions to Fix Issue:

• Check valve body for wear.
• Verify transmission fluid level and condition, considering the possibility of a clogged filter.
• Ensure proper functioning of the brake pedal switch, as it might override the throttle as a safety feature.
• Scope the 1st gear shift solenoid ground control or solenoid circuit amp coil ramp.
• Conduct pressure tests and check PID data for gear solenoid commands.
• Consider the possibility of issues in other systems like traction control, ABS, etc., which might affect engine control.
• Check the wiring harness near the left front headlight for broken wires.

Final Fix:

• The final fix involved replacing the brake pedal switch and clearing the code. The issue was resolved after numerous test drives and using different scan tools. The brake pedal switch was suspected because simulating the symptom by pushing both brake and gas pedals simultaneously replicated the problem.

Case #4: Chevrolet

Vehicle Information: 2002 Chevrolet Silverado 2500 HD 6.6L

Issue + Repair History:

• Started with a shorted positive battery cable, which welded to transmission cooler lines.
• High current caused one negative cable to catch fire.
• Post repairs, truck had U1000 (Class 2 Communication Error) and P1631 (Theft System Error).
• Replaced ECM and flash programmed it, restoring communication.
• Post-repair, ABS and BRAKE warning lights flash randomly when in gear.
• Turn signals behave erratically in gear.
• Intermittent communication with ABS, Body, and ECM.
• Sometimes U1000 and P0571 codes are present; other times no codes.
• Intermittent battery warning on monitor panel, despite good voltage reading.

Computer Codes & Descriptions:

• U1000: Class 2 Communication Error
• P0571: Brake Cruise Switch
• P1631: Theft System Error

Suggestions to Fix Issue:

• Check communication wires thoroughly.
• Consider replacing BCM and brake module.
• Inspect all wiring closely, especially those related to the battery feeds.
• Check all fuses in all fuse boxes for any blown during the short and fire.
• Inspect harnesses near all battery feed and along the transmission lines.
• Check secondary grounds from transmission and engine to body and frame.

Final Fix:

• Addressed multiple ‘ground gremlins’ caused by the main ground cable catching fire and burning off.
• Repaired 3 burned-off grounds: G110 and G302 (on frame behind driver’s door) and G100 (driver’s side frame at the front).
• The repairs resolved EBC and transfer case problems, communication errors, and all other erratic behaviors.
• Extensive test driving confirmed that all issues were resolved.

Case #5: Ford

Vehicle Information: 2006 Ford Focus LX Austero 2.0L

Issue + Repair History:

• Power steering warning light on with a message of power steering failure.
• Power steering functions normally during driving.
• Multiple fault codes present: U0073, U1900, U2012 (communication faults), P0231 (fuel pump monitoring fault), P0571 (brake pedal signal inconsistency), P2121 (throttle pedal position sensor inconsistency).
• No other warning lights and the car drives without other issues.
• Alternator replaced 2 months ago.

Other OBD2 Codes + Test Results:

• Network: U1900, U2012, U0073
• Engine: P0231, P0571, P2121

Suggestions to Fix Issue:

• Inspect the fuse box under the hood for loose connections, especially if the vehicle was in an accident.
• Go through CAN communication procedures to identify issues causing ‘U’ codes.
• Check the fuse box/multifunction junction box for loose pins or wiring damage.
• Ensure all modules are communicating properly.
• Check CAN wiring for any shorts or open circuits.

Final Fix:

• Found CAN wires had become untwisted and were running through power supply wires.
• Twisted CAN wires together and secured them to prevent untwisting.
• Uncertain if the issue was a bad connection at the fuse box or the untwisted CAN wires.
• Vehicle might have had prior accident damage or tampering with the fuse box.
• After repair, all issues resolved and customer satisfied.