DTC 21 & DTC 25 - Front Wheel Speed Sensor Circuit Fault: Notes

Toothed wheel generates a voltage pulse as it moves past sensor. EBCM uses these pulses to determine wheel speed. Amount of voltage generated in each pulse depends on wheel speed and air gap between sensor and toothed wheel.

EBCM uses wheel speed sensor signal to calculate vehicle reference speeds and individual speed, acceleration and slip values for each wheel. These values are used to determine when anti-lock control is needed.

DTC 21 or 25 will set if short to battery voltage or ground exists in circuit No. 833 or 872 (RF) or circuit No. 830 or 873 (LF). Faulty wheel speed sensor will also set DTC 21 or 25. Testing occurs when vehicle is moving. Fault will not set with ignition on and vehicle at rest.

If a fault is detected which causes a speed sensor DTC to set, anti-lock braking is disabled and EBCM turns on ANTI-LOCK indicator for remainder of ignition cycle. If failure is intermittent, EBCM will enable system at next ignition cycle and a history DTC will be present.

NOTE: To prevent electromagnetic interference, wheel speed sensor wires are twisted together 9 times per foot of wire. If repairs are necessary, ensure wires are properly twisted, routed and secured.

NOTE: Test numbers refer to numbers on diagnostic chart.

Checks for proper resistance of sensor.
Checks for short to voltage in either speed sensor circuit wire.
Checks for short between wheel speed sensor circuit wires.
Checks for short to ground in speed sensor input circuit wires. A short with a resistance less than 2 megohms, though not a hard short, can still cause DTCs to set.
Checks if DTC resets during road test.
Checks wiring and connectors for intermittents.
Replace wheel bearing/speed sensor assembly. If DTC resets, EBCM is concluding fault is present when no fault is present.
Ensures DTC is not due to electromagnetic interference.