Anti-Lock Braking System (ABS)

DTC C1020: Abnormality in RL wheel speed sensor circuit





















CAUTION:

- If there is any problem in the CAN bus lines, an incorrect DTC may be set. Prior to this diagnosis, diagnose the CAN bus lines

- Whenever ECU is replaced, ensure that the CAN bus lines are normal.

CIRCUIT OPERATION

- The wheel speed sensor is a kind of a pulse generator.
It consists of encoders (a plate on which north and south pole sides of the magnets are arranged alternately) for detecting the wheel speed which rotates at the same speed of the wheels and wheel speed sensors. This sensor outputs frequency pulse signals in proportion to the wheel speed.

- The pulse signals, which the wheel speed sensor creates, are sent to ABS-ECU. ABS-ECU uses the frequency of the pulse signals to determine the wheel speed.

DTC SET CONDITIONS

ABS-ECU monitors the voltage fluctuation in each wheel speed sensor circuit. If ABS-ECU detects the open or short circuit in the circuit, it will set a DTC.

PROBABLE CAUSES

Current trouble

- Damaged wiring harness and connectors

- Noise interference

- Malfunction of wheel speed sensor

- Malfunction of ABS-ECU

Past trouble

- Carry out diagnosis with particular emphasis on wiring harness and connector failures between ABS-ECU and the wheel speed sensor. For diagnosis procedures, refer to How to treat past trouble

DIAGNOSIS

Required Special Tools:

- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)

- MB991827: M.U.T.-III USB Cable

- MB991910: M.U.T.-III Main Harness A

- MB991974: ABS check harness

STEP 1. Using scan tool MB991958, diagnose the CAN bus lines.

Use scan tool to diagnose the CAN bus lines.

Q. Is the check result normal?

YES Go to Step 3.
NO Repair the CAN bus lines
STEP 2. DTC recheck after resetting CAN bus lines

Q. Is the DTC C1020 set?

YES Go to Step 3.
NO The procedure is complete.
STEP 3. Using scan tool MB991958, check the data list

Check the following service data (Refer to Data List Reference Table).

- Item No.03: RL wheel speed sensor

Q. Is the check result normal?

YES Go to Step 12.
NO Go to Step 4.
STEP 4. Voltage measurement at the A-03 ABS-ECU connector





(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and then measure the voltage at the special tool connector side.
NOTE:
Do not connect the special tool to ABS-ECU.

(2)Turn the ignition switch to the ON position.
(3)Measure the voltage between the rear wheel speed sensor (LH) power supply terminal
(signal terminal) No.24 and body ground, and between the ground terminal No.25 and body ground.
OK: 1 V or less

Q. Is the check result normal?

YES Go to Step 5.

NO (Not normal at the terminal No.24 or 25) : Go to Step 6.

STEP 5. Resistance measurement at A-03 ABS-ECU connector





(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and then measure the resistance at the special tool connector side.
NOTE:
Do not connect the special tool to ABS-ECU.

(2)Measure the resistance between the rear wheel speed sensor (LH) power supply terminal
(signal terminal) No.24 and body ground, and between the ground terminal No.25 and body ground.
OK: No continuity

Q. Is the check result normal?

YES Go to Step 8.

NO (Not normal at the terminal No.24 or 25) : Go to Step 6.

STEP 6. Connector check: A-03 ABS-ECU connector, C-39 and D-15 intermediate connector, F-21 rear wheel speed sensor (LH) connector

Q. Is the check result normal?

YES Go to Step 7.
NO Repair the defective connector. Then go to Step 13.
STEP 7. Wiring harness check between A-03 ABS-ECU connector terminal No.24 and F-21 rear wheel speed sensor (LH) connector terminal No.1, and between A-03 ABS-ECU connector terminal No.25 and F-21 rear wheel speed sensor (LH) connector terminal No.2.

- Check for short circuit in rear wheel speed sensor (LH) circuit

Q. Is the check result normal?

YES Replace the wheel speed sensor [RL] (Refer to Anti-Lock Braking System (ABS)). Then go to Step 13.
NO Repair the wiring harness. Then go to Step 13.
STEP 8. Voltage measurement at the A-03 ABS-ECU connector





(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the ABS-ECU-side connector and harness-side connector, and then measure the voltage at the special tool connector side.
(2)Turn the ignition switch to the ON position.
(3)Measure the voltage between the rear wheel speed sensor (LH) power supply terminal
(signal terminal) No.24 and body ground, and between the ground terminal No.25 and body ground.
OK:

Terminal No.24 and body ground: Battery positive voltage
Terminal No.25 and body ground: 1 V or less

Q. Is the check result normal?

YES Go to Step 9.

NO Go to Step 11.

STEP 9. Wiring harness check between A-03 ABS-ECU connector terminal No.24 and F-21 rear wheel speed sensor (LH) connector terminal No.1, and between A-03 ABS-ECU connector terminal No.25 and F-21 rear wheel speed sensor (LH) connector terminal No.2.

- Check for open circuit in rear wheel speed sensor (LH) circuit

Q. Is the check result normal?

YES Go to Step 10.
NO Repair the wiring harness. Then go to Step 13.
STEP 10. Check for wheel speed sensor [RL] as a single unit

Refer to Wheel Speed Sensor Inspection.

Q. Is the check result normal?

YES Go to Step 11.
NO Replace the wheel speed sensor [RL] (Refer to Anti-Lock Braking System (ABS)). Then go to Step 13.
STEP 11. Connector check: A-03 ABS-ECU connector, C-39 and D-15 intermediate connector, F-21 rear wheel speed sensor (LH) connector

Q. Is the check result normal?

YES Go to Step 12.
NO Repair the defective connector. Then go to Step 13.
STEP 12. Check whether the DTC is reset.

(1)Erase the DTC.

(2)Drive the vehicle at 12mph (20 km/h) or higher.
NOTE:
The ABS warning light does not turn OFF in some cases unless the vehicle runs at 12mph
(20 km/h) or higher.

Q. Is DTC C1020 set?

YES Replace the hydraulic unit (integrated with ABC-ECU) (Refer to Anti-Lock Braking System (ABS)). Then go to Step 13.
NO Intermittent malfunction How to Cope With Intermittent Malfunctions).
STEP 13. Check whether the DTC is reset.

(1)Erase the DTC.

(2)Drive the vehicle at 12mph (20 km/h) or higher.
NOTE:
The ABS warning light does not turn OFF in some cases unless the vehicle runs at 12mph
(20 km/h) or higher.

Q. Is DTC C1020 set?

YES Return to Step 1.
NO The procedure is complete.