To diagnose the ABS and PSM systems, you will need an OBD-II scanner to read and clear Porsche specific fault codes. Generic OBD-II scanners are not able to access those systems and will not show a fault code.
Common problems that trigger Porsche ABS and PSM lights to stay on include:
ABS Wheel Speed Sensor
One of the most common issues that trigger Porsche ABS or PSM lights to come on is a faulty ABS wheel speed sensor. Sensors can fail and stop sending wheel speed readings to ABS modules. They can also get damaged by rocks as well.
If you have an OBD-II scanner that can read faults from the ABS module, you can go to ABS or PSM control unit then, under that, select Live Data. Here you can see speed values from all the wheels as you carefully drive the vehicle.
Replacing the Porsche ABS wheel speed sensor is a straightforward procedure that you can perform yourself.
Check the wire harness if the ABS/PSM light stays on and the fault code still indicates a faulty ABS sensor. If the wire harness from the sensor to the ABS module is fine, the ABS module might be at fault.
Mass Air Flow (MAF) Sensor
It may sound unrelated, but a faulty MAF sensor or vacuum leak can trigger ABS and PSM fault lights to come on, especially if those warning lights come on during hard acceleration.
When you read the codes, you may get DME fault codes such as 5525 - Torque transmission disturbed at times or P0102 - Mass or Circuit Airflow (MAF) Circuit Low Voltage Input.
It is strongly recommended that you install a genuine Porsche MAF sensor made by Bosch, the OEM supplier. Also, avoid using air filters that need frequent oiling.
ABS Module / Pump
The ABS module is the "brains" of ABS and PSM systems. It controls the brake pressure sent to each wheel. It also adjusts the braking force to those wheels when the PSM system detects that the vehicle has lost traction.
Porsche ABS module can fail for several reasons:
- loose terminals
- Weak joints inside the module, causing intermittent ABS/PSM light.
- worn brushes for the ABS motor typical on high mileage Porsche
- corrosion at the ABS terminals
- Brake fluid leaking on the ABS pump, causing loss of communication with multiple wheel speed sensors.
Bosch makes ABS modules installed on many Porsche vehicles as Porsche doesn't make their own ABS module.
If your mechanic determines that the ABS module is faulty, it can be replaced with a used unit, but it may require coding. A cheaper alternative is to have your existing Porsche ABS Module Repaired by using these companies that offer this service on eBay.
Steering Angle Sensor
The steering angle sensor (SAS) sends data to the PSM module to let it know which way the steering wheel is turned. The steering angle sensor may be out of calibration and send the wrong information to the PSM module.
The steering angle sensor and clock spring are integrated into one piece and need to be replaced as one unit on some models. Before you replace this expensive part, carry out steering angle calibration to often fix the ABS and PSM problems.
The steering angle sensor is located on the steering column. To replace it, you will need to remove the steering wheel. You need to have the battery disconnected, or you will trigger the airbag light. Once you return the SAS, you need to carry out steering angle sensor calibration.
Brake Light Switch
If you are getting ABS failure and PSM failure, drive to the workshop message on the dashboard; when you press the brake pedal or start to drive, the problem may be the brake light switch.
This problem can affect any Porsche, including 911, Cayman; the brake light switch is very inexpensive and takes only a few minutes to replace. The Porsche brake light switch is mounted above the brake pedal.
You can't determine if the brake light switch is defective or not by looking at the brake lights.
To determine why your Porsche ABS and PSM lights come on, you need to diagnose the problem. Start by reading the fault codes from the ABS module. Do not replace parts based on what you read online.
Pay attention when installing a new brake light switch. The switch has a self-adjusting mechanism. Check the operation of the plunger after you replace the brake light switch.
Related fault codes: P0571, P1574 - Brake switch signal implausible. 4340 stop light switch defective, Porsche DME fault code 364.
If your Porsche ABS light is caused by no signal coming from the wheel speed sensor, inspect, clean, and, if needed, replace the faulty wheel speed sensor.