C1221

EBCM/Left Front Wheel Speed Sensor Schematic:

CIRCUIT DESCRIPTION
As a toothed ring passes by the wheel speed sensor, changes in the electromagnetic field cause the wheel speed sensor to produce a small AC voltage signal whose frequency is proportional to wheel speed.

CONDITIONS FOR SETTING THE DTC
This Diagnostic Trouble Code (DTC) will set when the following conditions are met:
^ Left front wheel speed is equal to zero for greater than 1.6 seconds while the other two wheel speeds are greater than 8 km/h (5 mph) and within 11 km/h (7 mph).
^ This DTC can be set when vehicle speed is above 8 km/h (5 mph).

ACTION TAKEN WHEN THE DTC SETS
A malfunction DTC is stored, ABS is disabled, and the amber ABS indicator lamp is turned ON.

CONDITIONS FOR CLEARING THE DTC
^ Conditions for the malfunction are no longer present and the Tech 2 scan tool Clear DTC Information function is used.
^ One hundred drive cycles have passed with no malfunctions detected.

DIAGNOSTIC AIDS
The following list contains items that need to be inspected when diagnosing this system:
^ Wheel speed sensor physically damaged.
^ Wheel speed sensor input circuits shorted together.
^ Missing speed sensor ring.
^ Excessive wheel speed sensor gap.

NOTE: Two separate wheel speed =0 DTCs will be set if two wheel speeds are 0 km/h (0 mph) for greater than 20 seconds while the remaining wheel speed(s) are greater than 16 km/h (10 mph) and within 11 km/h (7 mph).

An Intermittent Malfunction - is most likely caused by a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation. The frequency of the malfunction can be checked by using the Enhanced Diagnostic function of the Tech 2 scan tool, as described in Enhanced Diagnostics.

NOTE: Resistance of the wheel speed sensor will increase with an increase in sensor temperature.

When Measuring For A Short To Ground - in a wheel speed sensor wiring circuit, manually switch the J 39200 (Digital Multimeter) to the Meg-Ohms range. This will ensure a high resistance short to ground can be found. See J 39200 owners manual. When replacing a wheel speed sensor, inspect the sensor terminals and jumper harness connector for corrosion and/or water intrusion. If evidence of corrosion or water intrusion exists, replace both the wheel speed sensor and the jumper harness.

DTC C1221 Left Front Wheel Speed Sensor Input Signal = 0 (Part 1 Of 2):

DTC C1221 Left Front Wheel Speed Sensor Input Signal = Of (Part 2 Of 2):

TEST DESCRIPTION
The numbers below refer to step numbers on the diagnostic table.
[5] Checks wheel speed sensor resistance.
[6] Checks for voltage output from wheel speed sensor.
[7] Ensures that the wheel speed sensor wires are not shorted together.
[11] Checks if this DTC resets after a drive cycle.
[12] Checks the wheel speed sensor output compared to the other two.