Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Antilock Brake Module (MK25E): Operation: Notes
The primary functions of the Antilock Brake Module (ABM) are to:
- monitor the Antilock Brake System (ABS) for proper operation.
- detect wheel locking or wheel slipping tendencies by monitoring the speed of all four wheels of the vehicle.
- control fluid modulation to the wheel brakes while the system is in an ABS mode or the traction control system is activated.
- store diagnostic information.
- provide communication to the scan tool while in diagnostic mode.
The ABM constantly monitors the antilock brake system for proper operation. If the ABM detects a fault, it will send a message to the mechanical instrument cluster (MIC) instructing it to turn on the amber ABS warning indicator lamp and disable the antilock braking system. The normal base braking system will remain operational.
The ABM continuously monitors the speed of each wheel through the signals generated by the wheel speed sensors to determine if any wheel is beginning to lock. When a wheel locking tendency is detected, the ABM commands the ABM command coils to actuate. The ABM command coils then open and close the valves in the HCU that modulate brake fluid pressure in some or all of the hydraulic circuits. The ABM continues to control pressure in individual hydraulic circuits until a locking tendency is no longer present.
The ABM contains a self-diagnostic program that monitors the antilock brake system for system faults. When a fault is detected, the amber ABS warning indicator lamp is turned on and the fault diagnostic trouble code (DTC) is then stored in a diagnostic program memory. These DTC's will remain in the ABM memory even after the ignition has been turned off. The DTC's can be read and cleared from the ABM memory by a technician using a scan tool. If not cleared with a scan tool, the fault occurrence and DTC will be automatically cleared from the memory after the identical fault has not been seen during the next 3, 500 miles of vehicle operation.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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