SureTrack Community Fix: Bad Signals

Real Fixes from the SureTrack® expert information resource are documented issues from actual shop repair orders and community discussions. Read on to see how SureTrack can help you correct issues that are not easily diagnosed using OEM information alone. SureTrack is currently available free with the purchase of a current Snap-on® diagnostic software version.

Anti-lock brakes and traction control systems have been standard on vehicles for many years now. These important safety features rely on good signals from various components to work properly. Follow this Real Fix to see how a code C0050 on a Chevrolet Tahoe was diagnosed and the components that caused the problem were determined.

Vehicle
2014 Chevrolet Tahoe LTZ 5.3L

Title
C0050, Replaced Anti-Lock Brake Traction Control Module, ABS Wheel Speed Sensor

Complaint
The customer states the anti-lock brake system (ABS) light is on.

Cause
Connected a scan tool and found code C0050 – Right Rear Wheel Speed Sensor Circuit. With the scan tool connected, cleared the codes, performed a road test, monitored the ABS wheel speed sensors and found no signal parameter from the right rear ABS wheel speed sensor. Raised the vehicle on a lift and inspected the right rear ABS wheel speed sensor connector, terminals and wiring harness and found no faults. Key on, back-probed the right rear ABS wheel speed sensor, and monitored the sensor signal frequency and amplitude with a lab scope while spinning the wheel by hand. The right rear ABS wheel speed sensor did not produce an observable signal or waveform. Disconnected the connector for the right rear ABS wheel speed sensor. Key on, used a multi-meter to measure the specified 12 Volts at terminal “A” of the ABS sensor connector and found the voltage was not present. Key on, used the multi-meter, back-probed the connector at the anti-lock brake traction control module for the right rear ABS wheel speed sensor and found the 12 Volt supply was not present. Disconnected the connector for the anti-lock brake traction control module, inspected the terminals, connector and wiring harness and found no faults. Replaced and programmed the anti-lock brake traction control module and continued diagnostics. Key on, ABS wheel speed sensor disconnected, used the multi-meter to measure the 12 Volt supply and the 1.0 Volt control side bias voltage at the connector and found both were present. Connected the right rear ABS wheel speed sensor, back-probed the sensor with the lab scope. Spun the right rear wheel, as the wheel RPM increases frequency (HZ) should also increase with no dropouts or glitches during the test. While spinning the right rear wheel the lab scope digital square wave signal was erratic and had dropouts. These test results verified the anti-lock brake traction control module and the right rear ABS wheel speed sensor were faulty.

Correction
Replaced the anti-lock brake traction control module and ABS wheel speed sensor, cleared codes, performed a road test and verified the vehicle operated properly. The ABS light did not illuminate and no fault codes returned.


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About the Author

Nick Taylor

Nick Taylor is the SureTrack Community Administrator and a Senior Applications Specialist at Mitchell 1 with over 25 years of experience with electronic repair data systems. Nick previously worked in the automotive dismantling and engine rebuilding industries.