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 (Refer to GROUP 54C - Diagnostic trouble code diagnosis ).
Whenever ECU is replaced, ensure that the CAN bus lines are normal.
When the hydraulic unit (integrated with ASC-ECU) is replaced, always carry out the calibration of the steering wheel sensor, the G and yaw rate sensor and brake fluid pressure sensor (Refer to , and ).

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 ASC-ECU. ASC-ECU uses the frequency of the pulse signals to determine the wheel speed.

DTC SET CONDITIONS

ASC-ECU monitors the voltage fluctuation in each wheel speed sensor circuit. If ASC-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 ASC-ECU

Past trouble

Carry out diagnosis with particular emphasis on wiring harness and connector failures between ASC-ECU and the wheel speed sensor. For diagnosis procedures, refer to How to treat past trouble (GROUP 00 - How to Cope with Intermittent Malfunction ).

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

MB991997: ASC check harness

STEP 1. M.U.T.-III CAN bus diagnosis

Use scan tool to diagnose the CAN bus lines.

Q. Is the check result normal?

	Go to Step 3.

	Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostic table ). On completion, go to Step 2.

STEP 2. DTC recheck after resetting CAN bus lines

Q. Is DTC C1020 set?

	Go to Step 3.

	The procedure is complete.

STEP 3. M.U.T.-III data list

Check the following service data (Refer to

Item No.03: RL wheel speed sensor

Q. Is the check result normal?

	Go to Step 12.

	Go to Step 4.

STEP 4. Voltage measurement at the A-51 ASC-ECU connector

(1)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the voltage at the special tool connector side.

note

Do not connect the special tool to ASC-ECU.

(2)Turn the ignition switch to the ON position.
(3)Measure the voltage between the wheel speed sensor power supply terminal (signal terminal) No.36 and the body ground, and between the wheel speed sensor ground terminal No.37 and the body ground.
OK: 1 volt or less

Q. Is the check result normal?

Go to Step 5.

NO (Not normal at the terminal No.36 or 37)

: Go to Step 6.

STEP 5. Resistance measurement at A-51 ASC-ECU connector

(1)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the resistance at the special tool connector side.

note

Do not connect the special tool to ASC-ECU.

(2)Resistance between the wheel speed sensor power supply terminal (signal terminal) No.36 and the body ground, and between the wheel speed sensor ground terminal No.37 and the body ground.
OK: No continuity

Q. Is the check result normal?

Go to Step 8.

NO (Not normal at the terminal No.36 or 37)

: Go to Step 6.

STEP 6. Connector check: A-51 ASC-ECU connector, C-39 intermediate connector, D-15 intermediate connector, F-21 wheel speed sensor <RL> connector

Q. Is the check result normal?

	Go to Step 7.

	Repair the defective connector. Then go to Step 13.

STEP 7. Wiring harness check between A-51 ASC-ECU connector terminal No.36 and F-21 wheel speed sensor <RL> connector terminal No.1, and between A-51 ASC-ECU connector terminal No.37 and F-21 wheel speed sensor <RL> connector terminal No.2.

Check for short circuit in wheel speed sensor <RL> circuit

Q. Is the check result normal?

	Replace the wheel speed sensor <RL> (Refer to ). Then go to Step 13.

	Repair the wiring harness. Then go to Step 13.

STEP 8. Voltage measurement at the A-51 ASC-ECU connector

(1)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the ASC-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 wheel speed sensor circuit power supply terminal (signal terminal) No.36 and the body ground.
OK: Battery positive voltage

Q. Is the check result normal?

Go to Step 9.

Go to Step 11.

STEP 9. Wiring harness check between A-51 ASC-ECU connector terminal No.36 and F-21 wheel speed sensor <RL> connector terminal No.1, and between A-51 ASC-ECU connector terminal No.37 and F-21 wheel speed sensor <RL> connector terminal No.2.

Check for open circuit in wheel speed sensor <RL> circuit

Q. Is the check result normal?

	Go to Step 10.

	Repair the wiring harness. Then go to Step 13.

STEP 10. Check for wheel speed sensor as a single unit

Refer to

Q. Is the check result normal?

	Go to Step 11.

	Replace the wheel speed sensor <RL> (Refer to ). Then go to Step 13.

STEP 11. Connector check: A-51 ASC-ECU connector, C-39 intermediate connector, D-15 intermediate connector, F-21 wheel speed sensor <RL> connector

Q. Is the check result normal?

	Go to Step 12.

	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 12 mph (20 km/h) or more.

note

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

Q. Is DTC C1020 set?

	Replace the hydraulic unit (ASC-ECU) (Refer to ). Then go to Step 13.

	Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).

STEP 13. Check whether the DTC is reset.

(1)Erase the DTC.

(2)Drive the vehicle at 12 mph (20 km/h) or more.

note

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

Q. Is DTC C1020 set?

	Return to Step 1.

	The procedure is complete.