ABS Wheel Sensor Resistance '97 Lesabre

[Smith1000]

The ABS light is stuck on in my wife's car and it has been for some time. The car does not currently have functioning ABS. It stops okay, just no ABS. I am about to test wheel sensor resistance with a digital ohm meter to try to identify the bad wheel sensor (if that is the problem). Was just wondering if anyone knows what resistance value I should look for or will the bad one be the sensor with no value at all (possibly)? Thanks.

[BNaylor]

Ballpark figure is around 1K ohms. The bad one will show abnormally higher or lower resistance especially compared to the good ones or an open (no reading).

[jerryls]

I just had to repalce mine on a 94. It was an open circuit. The new one read about 1500 ohms.

[Blue Bowtie]

If a wheel speed sensor is out of the acceptable resistance range, the ABS warning should turn on and remain on when the ignition is turned on. If the warning lamp cycles on then back off after a few seconds, that usually means the wheel senor circuits are within the acceptable resistance range. This power-on test is intended to check for speed sensor circuit continuity and shorts.

If all the wheel speed sensor circuits pass the resistance test, you can test the output of each sensor. Connect your AC voltmeter to the sensor leads. Spin the hub or wheel at about 1 revolution per second (approximately 5 MPH). Read the AC voltage produced by each sensor. Rear sensors should produce a minimum of about 0.6VAC, front sensors should produce a minimum of about 0.9VAC. Lack of adequate signal from a sensor will set a code as soon as the vehicle is moving about 5-7 MPH. The EBCM actually reads the frequency of the sensor signals, but the AC output voltage is a good indication of sensor performance.

Each wheel sensor harness should also have a DC bias voltage when the ignition is on. The wheel speed sensor connector (vehicle harness end) should have between 2.5-5VDC at each wheel. Lack of a bias voltage can indicate a wire harness or EBCM problem.

The EBCM also relies on a VSS signal from the PCM. If the wheel sensors check out as normal, and the ABS warning lights at about 5-7 MPH, that can indicate the lack of a VSS signal (the EBCM is receiving all wheel speed signals but no vehicle speed signal).

Other things to check are the brake fluid level sensors, brake pedal switches, and the rear/center brake lamp. Some systems use the brake pedal switch and filament of the center brake lamp as redundant inputs, and a failed center brake lamp can cause the ABS warning to light (as well as cause the cruise control to be inoperative).

[BNaylor]

Originally Posted by jerryls

I just had to repalce mine on a 94. It was an open circuit. The new one read about 1500 ohms.

Thanks for the input. Sometimes the resistance test works and times it doesn't prove anything. But a good practice nonetheless. Also, wiring at the lower control arm, the electrical connector and wiring leading up to the EBTCM module are possibiities. Often overlooked is the EBTCM module itself if you can find it. On later Bosch 5.3 ABS systems used it is located at the ABS modulator/pump assembly.

According to the '97 GM Factory Service Manual (FSM) the proper resistance range and reading for a wheel sensor associated with a GM ABS VI braking system is:

Front - 1020-1137 Ohms @ 68 degress F.

Rear - 1020-1180 ohms @ 68 degress F.