Test 12A - Left Front Wheel Speed Sensor

Test 12A: Repairing -- Left Front Wheel Speed Sensor (Part 1 Of 2):

Test 12A: Repairing -- Left Front Wheel Speed Sensor (Part 2 Of 2):

Right Rear Wheel Speed Sensor Schematic:

ABS Electrical Layout:

Left Front Wheel Speed Sensor Connector:

NOTE: You must perform Test 1A, before performing this test.

LF WHEEL SPEED SENSOR

When Its Monitored
Vehicle speed is above 8 mph, or the 2 highest wheels are above 15 mph.

Set Condition
The wheel speed sensor codes are set when the Controller Antilock Brake (CAB) fails to detect a signal from one or more sensors The missing sensor signal(s) must be missing for greater than 2.5 seconds or 20 seconds in the case of both rear wheels missing (the second case is to prevent false codes caused by excess front wheel spin such as a snowbound vehicle). The code indicates wire continuity exists, but the sensor signal is interrupted or not being generated. If a wheel speed sensor circuit continuity problem occurs, this trouble code will also exist.

Possible Causes:
^ Wheel speed sensor loose at wheel
^ Damaged wheel speed sensor
^ Damaged tone wheel
^ Hydroplaning at high speed
^ Intermittent open sensor circuit
^ Wheel lockup during Antilock Brake System (ABS) stop
^ Missing tone wheel
^ Excess sensor gap or runout

LF WSS ERRATIC SIGNAL

When Its Monitored
The test is conducted when the vehicle is not in ABS cycling.

Set Condition
Each wheel is equipped with a metal tone wheel with a number of evenly spaced teeth. A wheel speed sensor generates a small AC signal as each tooth passes the sensor face. The CAB monitors the wheel speed signals every 5ms. The trouble code is stored if six wheel speed sensor signal fluctuations are observed that seem too fast to be real.

Possible Causes:
^ Damaged tone wheel
^ Tone wheel missing a section of teeth
^ Excessive gap between the sensor & tone wheel
^ 0ut of round tone wheel

LF WSS MISSING SIGNAL

When Its Monitored
The test is conducted when the vehicle speed is greater than 8 mph or the two highest wheels are greater than 15 m ph. The test is also run when both front wheels are above 15 mph and the rear wheels are below 0.5 mph.

Set Condition
Each wheel is equipped with a metal tone wheel with a number of evenly spaced teeth. A wheel speed sensor generates a small AC signal as each tooth passes the sensor face. The CAB monitors the wheel speed signals every 5ms. The trouble code is stored if there are no speed transitions on one or two wheels for more than 2.5 seconds or no speed transitions from one or both rear wheels for more than 20 seconds.

Possible Causes:
^ Wheel speed sensor (+) and (-) circuits shorted together
^ Failed wheel speed sensor
^ Missing tone wheel
^ Excessive gap between the sensor and tone wheel
^ WSS continuity code
^ Two rear tone wheels missing
^ Vehicle stuck or front wheel spin with no vehicle movement
^ Tires hydroplaning at high speed