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In a previous video, we talked about ABS code C1158 and how it was activated by the customer driving and disturbing the air gap on the wheel speed sensor. This video below discusses wheel speed sensor codes that can occur the second the key is turned.
By the time a driver puts their vehicle in gear, the ABS system knows the health of the wheel speed sensor circuits. It does this by sending a known voltage through the circuit. If no voltage comes back, the ABS system knows there is an open or break in the circuit. If the same voltage comes back, the circuit is shorted to ground. If too much voltage comes back, it is a short to power. If not the right amount of power comes back, it knows there is high or low resistance in the circuit at the sensor or in the wire.
This test is called a bias voltage test and every vehicle does it. If the results do not match the specification, it turns off power to the affected circuit, disables the ABS system and sets a code. In this video, Andrew Markel discusses how to decipher the codes and diagnose the circuit. This video is sponsored by BCA Bearings.