DTC 21

DTC 21 Right Front Wheel Speed Sensor Malfunction






Circuit Description

As each wheel turns, the signal generated by each wheel speed sensor is sent to the EBTCM. The EBTCM uses the 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 antilock or traction control is required.

The EBTCM will only set one wheel speed sensor fault code at a time, even if multiple faults exist. Detection is prioritized accordingly: LF, RR, LR, RF. Always check for additional stored codes after making repairs.

DTC will set when

DTC 21 will set if the RF speed signal is not detected by the time the vehicle reaches 7.5 mph (12 kph) on initial drive-off or the signal is lost while driving at a speed greater than 25 mph (40 kph).

Code 21 is set if there is a short to voltage or ground in CKT 872 or 833, or faulty speed sensor. The testing for this fault occurs when the vehicle is in motion, it will not set with the ignition "ON" and the vehicle at rest.

A Code 21 may set if CKT 872 or 833 lose continuity and the WSS signal is lost while driving. A Code 23 should accompany this code on the subsequent ignition cycle. If both Code 21 and Code 23 are set concurrently, diagnose Code 23 first.

Action Taken

1. Code set.
2. ABS/TCS switched "OFF".
3. "ANTILOCK" indicator "ON".
4. "TRACTION DISABLED" message displayed.

Test Description

Test numbers refer to circled numbers on the diagnostic chart.

1. Checks if the code resets during a road test.
2. Use the TECH 1 to check for sources of induced electrical noise. See Diagnostic Aids.
3. Checks for damaged wheel speed sensor and/or loose circuit connections.
4. Checks for intermittent opens/shorts in wheel speed sensor circuits and cables.
5. Checks for proper resistance in the sensor itself.
6. Checks for a short to battery in either of the speed sensor circuit wires.
7. Checks for a short between the speed sensor circuit wires
8. & 9. Checks for a short to ground in the speed sensor input circuit wire. The ground may be either a "hard" short to ground, or a resistive short. A short with a resistance less than 2 M ohms, though not a hard short, can still cause Code 21 to set.

Diagnostic Aids

Some sources of induced electrical noise which may cause intermittent wheel speed sensor codes to set are: improper routing or sensor cables next to spark plug wires; faulty spark plug wires; cables not retained in brackets; poor terminal engagement of connectors; or intermittent shorts or opens in wiring; or a loss of sensor circuit shield.

The shield is a foil insulator that is wrapped around the wheel speed sensor circuits. Inside the EBTCM harness connector there is an uninsulated drain wire that is attached to the shield and then to the wheel speed sensor return line and taken to ground through the EBTCM. It may be necessary to disassemble the EBTCM connector to check if the drain wire has a poor connection with the wheel speed sensor return connector terminal.