DTC 21
DTC 21: Wheel Speed SensorWheel Speed Sensor Circuit
Part 1 of 2
Part 2 of 2
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 voyage 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 wires 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 are 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 or 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 Tools:
- MB991223: Harness Set
- MB991502: Scan Tool (MUT-II)
- MB991529: Diagnostic Trouble Code Check Harness
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 and go to Step 9.
STEP 2. Check wheel speed sensor circuit at the ABS-ECU connector Add.
1. Disconnect the 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, or 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, or 8 and 9 within the standard value?
YES: Go to Step 6.
NO: Terminals 6 and 7>: Go to Step 3.
NO: Terminals 4 and 5>: Go to Step 4.
NO: Terminals 1 and 3, 8 and 9>: Go to Step 5.
STEP 3. Check the harness wires between the ABS-ECU connector A-02 and the wheel speed sensor Front: LH> connector A-22.
NOTE: After inspecting the intermediate connector C-06, inspect the wires. If the intermediate connector C-06 is damaged, repair or replace it. If the connector has been repaired or replaced, go to Step 9.
Q: Is any of the harness wires between the ABS-ECU connector A-02 and the wheel speed sensor Front: LH> connector A-22 damaged?
YES: Repair it and go to Step 9.
NO: Go to Step 7.
STEP 4. Check the harness wires between the ABS-ECU connector A-02 and the wheel speed sensor Front: RH> connector A-37.
Q: Is any of the harness wires between the ABS-ECU connector A-02 and the wheel speed sensor
YES: Repair it and then go to Step 9.
NO: Go to Step 7.
STEP 5. Check the harness wires between the ABS-ECU connector A-02 and the wheel speed sensor connectors D-08
NOTE: After inspecting the intermediate connector C-90, C-94 or D-16, inspect the wires. If the intermediate connector C-90, C-94 or D-16 is damaged, repair or replace it. If the connector has been repaired or replaced, go to Step 9 .
Q: Is any of the harness wires between the ABS-ECU connector A-02 and the wheel speed sensor connectors D-08
YES: Repair it and then go to Step 9.
NO: Go to Step 7.
STEP 6. Check me 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 a damage in any of the following check items, replace the wheel speed sensor or the ABS rotor.
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
Q: Is me wheel speed sensor or ABS rotor damaged?
YES: Replace the faulty part and then go to Step 9.
NO: Go to Step 8.
STEP 8. Check the wheel bearing.
Q: Is me 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 me diagnostic trouble codes 11, 12, 13, 14, 21, 22, 23 or 24 reset?
YES: Go to Step 1.
NO: This diagnosis is complete.