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Error Code P0571 is defined as Cruise Control/Brake Switch A Circuit Malfunction, meaning the switch that deactivates the cruise control system which causes the cruise control is malfunctioning.
This code is a generic trouble code, meaning it applies to all vehicles that come with the OBD-II system, especially those made since 1996 up to present. It’s particularly common among Audi, Cadillac, Chevrolet, Chrysler, Dodge, GMC, Harley, Jeep, Kia, Mazda, Peugeot, Volkswagen, and Volvo.
The PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes), monitors multiple different sensors and switches included in the proper functionality of the engine, and make sure everything is up and running properly (i.e., cruise control).
Many factors can alter the speed of the vehicle while driving down the road. New technology like the ACC (Adaptive Cruise Control) system can adjust the vehicle speed according to its surroundings (i.e. passing, lane departure, slowing for traffic, lane maneuvers, etc.).
In this code, the fault refers to the cruise control/brake switch “A” circuit malfunction. The proper operation of the brake switch is vital for the operation of the cruise control system. Given the fact that one of the many ways to turn off cruise control is by depressing the brake pedal, drivers need to take care of this function, especially if cruise control is used in daily commuting.
The “A” in the description refers to the specific wire, connector, harness, etc. Thus, pinpoint what exactly the code description refers, you will need to check it with your vehicle’s service manual. If you can’t seem to find what you need, then check the wiring diagram for the cruise control system; this will show you specific locations, specifications, wire colors, etc.
When Error Code P0571 is stored, that means there’s a problem with the switch that deactivates the cruise control when the brake pedal is depressed.
Other Cruise Control/Brake Switch A Circuit Malfunction and related codes include:
As with other codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other common symptoms include:
- Inoperative or erratic cruise control
- Certain cruise control functions not working properly (i.e., set, acceleration, or resume)
- Cruise control not engaging
- If brake light switch is faulty, then there are no brake lights
There are many reasons why this fault appears. Common possible causes for this code include:
- Defective brake switch/cruise control
- Defective cruise control buttons
- Damaged components in the cruise control system
- Wiring issues (i.e., chafed, pinched brake pedal, etc.)
- Debris, dirt caught in brake switch, hindering operation
- Brake switch out of its mount
- Brake switch out not correctly adjusted
- PCM issue (i.e., internal short, open, etc.)
How to Check
As with most codes, the best way to start the diagnosis for this code is to refer to the TSB (Technical Service Bulletins) for known troubleshooting and repairs for the specific vehicle. Advanced steps for diagnosis usually vary from one car make, model, year, or powertrain to another.
Check the brake switch under the dash. Usually, it’s mounted to the brake pedal arm itself. In many cases, the driver’s foot brake switch is entirely off of its mount, either broken or not mounted correctly, which can result to this code.
If this is the case, then you would have to replace the cruise control/brake switch with a new one. Make sure you follow instructions specified by the manufacturer for installation and adjustments, to avoid damage to the sensor, or even cause other issues.
Check the involved circuit. Refer to the wiring diagram of your service manual to determine the color codes and designation of the cruise control/brake switch A circuit. In most cases, to rule out the possibility of the fault in the harness, you can try to disconnect one end from the brake switch and the other from the PCM. Then, conduct a continuity test using a multimeter. Manufacturers usually provide specifications for you to compare the desired ones to the actual values. Generally, you will have to check the resistance of the circuit to determine any open, high resistance, etc. present.
When performing this test, make sure you check the pins in the connectors, switch, and PCM. In many cases, moisture can creep through the connectors and may cause an intermittent condition. For corrosion issues, remove rust using an electrical connection cleaner before reconnecting it again.
Check the PCM. It’s important to remember, sometimes with cruise control that it is the BCM (body control module) that monitors and adjusts this system. Then, pinpoint which one your system uses, then inspect for any water intrusion.
If you suspect anything in this step, and you’re not sure what to do, it is best to take your vehicle to your dealer or a reputable repair shop.
How to Fix
- Repair or replacement of faulty electrical components, connections, and wires
- Replace defective brake pedal and brake switch, then reset the code before taking the vehicle for a test drive
- If the code returns, the cause may be in the controls for the cruise control system of the vehicle, meaning, it must be checked. Repair or replace any damaged components
Cruise control system error codes are usually minor issues. However, since this code could potentially affect the brake switch and cause it to malfunction, it can be a safety concern.
One major role of a brake switch is to provide activation signal lights on your rear brake lights to inform fellow vehicles of your deceleration or braking.