DTC 21
DTC 21 - RF Wheel Speed Sensor
CIRCUIT OPERATION
- A toothed ABS rotor generates a voltage pulse as it moves across the pickup field of each wheel speed sensor.
- The amount of voltage generated at each wheel is determined by the clearance between the ABS rotor teeth and the wheel speed sensor, and by the speed of rotation.
- The wheel speed sensors transmit the frequency of the voltage pulses and the amount of voltage generated by each pulse to the ABS electronic control unit (ABS-ECU).
- The ABS hydraulic unit modulates the amount of braking force individually applied to each wheel cylinder.
ABS DTC SET CONDITIONS
- DTCs 11, 12, 13, 14 are output when signal is not input due to breakage of the (+) or (-) wire of one or more of the four wheel-speed sensors. DTCs 21, 22, 23, 24 are output in the following cases:
- Open circuit is not found but no input is received by one or more of the four wheel-speed sensors at 10 km/h (6 mph) or more.
- Sensor output drops due to a malfunctioning sensor or warped ABS rotor.
TROUBLESHOOTING HINTS (The most likely causes for these DTCs to set are:)
DTC 11, 12, 13, 14
- Malfunction of the wheel speed sensor
- Damaged wiring harness or connector
- Malfunction of the hydraulic unit (Integrated with ABS-ECU) DTC 21, 22, 23, 24
- Malfunction of the wheel speed sensor
- Damaged wiring harness and connector
- Malfunction of the hydraulic unit (Integrated with ABS- ECU)
- Malfunction of the ABS rotor
- Malfunction of the wheel bearing
- Excessive clearance between the sensor and ABS rotor
DIAGNOSIS
Required Special Tool:
- MB991223: Harness Set
STEP: 1. Check the wheel speed sensor installation.
Q:Is the wheel speed sensor bolted securely in place at the front knuckle or the rear knuckle?
YES:Go to Step 2.
NO:Install it properly. Then go to Step 9.
STEP: 2. Check wheel speed sensor circuit at the ABS-ECU connector A-02.
1. Disconnect connector A-02 and measure at the harness side.
2. Measure the resistance between the ABS-ECU connector terminals 1 and 3, 4 and 5, 6 and 7, 8 and 9.
Standard Value: 1.28 - 1.92 k ohms
Q:Is the resistance between terminals 1 and 3, 4 and 5, 6 and 7, 8 and 9 within the standard value?
YES: Go to Step 6.
NO:Go to Step 3,4 or 5.
STEP: 3. Check the harness wires between ABS-ECU connector A-02 and wheel speed sensor
NOTE: After inspecting intermediate connector C-05, inspect the wire. If intermediate connector C-05 is damaged, repair or replace it. If the connector has been repaired or replaced, go to Step 9.
Q:Are any harness wires between ABS-ECU connector A02 and wheel speed sensor
YES:Repair them and go to Step 9
NO:Go to Step 7.
STEP: 4. Check the harness wires between ABS-ECU connector A-02 and wheel speed sensor
Q:Are any harness wires between ABS-ECU connector A 02 and wheel speed sensor
YES:Repair them and then go to Step 9
NO:Go to Step 7.
STEP: 5. Check the harness wires between ABS-ECU connector A-02 and wheel speed sensor connector D-11
NOTE: After inspecting intermediate connectors C-212,C-210 and D-16, inspect the wire. If intermediate connector C-212,C210 or D-16 is damaged, repair or replace it. If the connector has been repaired or replaced, go to Step 9 .
Q:Are any harness wires between ABS-EQU connector A02 and wheel speed sensor connector D-11
YES:Repair them and then go to Step 9.
NO:Go to Step 7.
STEP: 6. Check the wheel speed sensor output voltage.
Output Voltage:
- When measured with a voltmeter: 42 mV or more
- When measured with oscilloscope (maximum voltage): 200 mV or more
Q:Does the voltage meet the specification?
YES:Replace the hydraulic unit (integrated with ABS-ECU) and then go to Step 9.
NO:Go to Step 7.
STEP: 7. Check the wheel speed sensor or ABS rotor. If there is damage in any of the check items, replace the wheel speed sensor.
Check items:
- Wheel speed sensor internal resistance
Standard value: 1.28 - 1.92 k ohms
- Insulation between the Wheel speed sensor body and connector terminals
- Toothed ABS rotor check
Q:Is the wheel speed sensor or ABS rotor damaged?
YES:Replace it and then go to Step 9.
NO:Go to Step 8.
STEP: 8. Check the wheel bearing.
Q:Is the wheel bearing damaged?
YES:Replace it and then go to Step 9.
NO:Go to Step 9.
STEP: 9. Check the diagnostic trouble codes.
Q:Do the diagnostic trouble codes 11, 12, 13, 14, 21, 22, 23 and 24 reset?
YES:Go to Step 1.
NO:This diagnosis is complete.