ABS issues still
 

had original ABS module rebuilt, but still having the same issues, so today drove to a dismantler and bought a used module and still having the same issues. So I am thinking maybe the issue is not the module.

Codes pulling P0571 (Brake Switch A Circuit) and P0504(Brake Switch A/B Correlation). Other symptoms ABS, skid and brake lights are all on along with brake failure stop carefully warning in the messages screen. trip odometer is dashes and cruise control does not work.

I am thinking there is a possibility of the wheel sensors, but was wondering how to test these to see if they are good or not as well as testing the brake pedal sensor on the brake booster.

Any help is greatly appreciated.

Thank you.

Mine is doing the same thing...took it to someone with the proper Volvo code reader and it came up that the left hand abs sensor was faulty. Will replace both at the same time. Still drives great and no issues with the brakes working.

Did replacing the abs sensors get rid of your codes ?

Have them check your brake pedal sensor too

Is there a way to check it myself cause there isn't a volvo garage or any repair shop that will have have one of the fancy volvo scan tools that is anywhere near me.

Only if you have a scanner. I was able to see the voltage going to the sensor, the distance the plunger was moving, as well as it turn ON/OFF when the brake pedal was pressed. It looks like a bitch to get out though and I havent found anyone that made a video about its removal. I found out that theres a C clip holding it in but you cant see it and you have to do it by feel. If you look at the brake pedal, theres 2 sensors. The blue and white one twists out but as far as I know, the black one is held in by a C clip.

The error codes you're encountering, P0571 and P0504, are related to the brake switch circuit. These codes often indicate issues with the brake pedal position sensor and can trigger the ABS, skid, and brake lights to come on. To diagnose the problem and test various components, you can follow these steps:

1. Check the Brake Pedal Position Sensor:
- Inspect the wiring and connector for the brake pedal position sensor. Make sure it's properly connected and that the wiring is not damaged. If the sensor is faulty, it may need to be replaced.

2. Test the Brake Pedal Position Sensor:
- You can test the brake pedal position sensor with a multimeter. Check for voltage changes as you press and release the brake pedal. It should send different voltage signals as the pedal moves.

3. Inspect Wheel Speed Sensors:
- To check the wheel speed sensors, you'll need to inspect the wiring and connectors at each wheel. Look for damaged wires, loose connections, or corroded connectors. Ensure they are properly connected to the ABS module.

4. Test Wheel Speed Sensors:
- Testing wheel speed sensors typically requires a digital multimeter and an oscilloscope. You can measure the resistance and voltage output of each sensor while spinning the wheels to see if they are sending the correct signals. If a sensor is faulty, it may need to be replaced.

5. Inspect ABS Rings and Tone Wheels:
- Ensure that the ABS rings and tone wheels at the wheels' hubs are clean and undamaged. Damaged or missing teeth on these components can affect the sensor readings.

6. Clear Error Codes: After checking and potentially fixing any issues, clear the error codes using an OBD-II scanner. If the issues were resolved, the warning lights should go off.

If you are unsure about any of these steps or if you can't pinpoint the problem, it's advisable to have a professional mechanic or technician perform a more in-depth diagnosis. They can use specialized diagnostic tools to identify and resolve the issue with greater accuracy. Brake system issues can affect safety, so it's crucial to ensure they are resolved correctly.