Mercedes Benz ABS Lamp On – False Activation
Aug. 01 2022
Aug. 01 2022

Vehicle: 2009 Mercedes Benz C 230 4MATIC (204.085), V6-2.5L (272.911)

Mileage: 122,368

Problem: This Mercedes came to the shop with the ABS lamp on, and at low speeds, it felt like the ABS was activating.

Case Details: When the technician went on a test drive with his scan tool connected, he noticed that when driving at about 5-7 mph, the ABS system falsely activated. Also, the right wheel speed sensor (WSS) was displaying no speed.

Mercedes Rear Wheel Speed Sensor

He replaced the right rear wheel speed sensor and went on another test drive. The right WSS was still showing no speed.

An ALLDATA Tech-Assist consultant advised checking the tone wheel (#5 in image) on the axle. They often get corroded and sometimes fall off. If the tone wheel was okay, the next thing to check would be the wiring and connectors from the WSS to the ABS module.

The technician inspected the tone wheel and found the right one was completely corroded.

Confirmed Repair: The technician replaced the tone wheel. On this test drive, the ABS light remained off and the brakes worked as designed. Problem solved!

The ALLDATA Tech-Assist team fields cases like this every day. See how Tech-Assist can help your shop save time and money with on-call diagnostic support from ASE-certified Master Technicians. More Tech Tips 

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