DTC C1020: Abnormality in RL wheel speed sensor circuit

caution

If there is any problem in the CAN bus lines, an incorrect diagnostic trouble code may be set. Prior to this diagnosis, diagnose the CAN bus lines.
Whenever the ECU is replaced, ensure that the CAN bus lines are normal.
When the hydraulic unit (integrated with ASC-ECU) is replaced, always perform the calibration of steering wheel sensor, G and yaw rate sensor, brake fluid pressure sensor, cut valve, and inlet valve.(Refer to , , , and .)

CIRCUIT OPERATION

Each wheel speed detecting section is a kind of a pulse generator. It consists of the encoder (plate on which the north and south pole of magnet are arranged alternately) for detecting the wheel speed, which rotates at the same speed of the wheels, and the wheel speed sensor. This detecting section outputs the frequency pulse signals in proportion to the wheel speed.
The pulse signals generated by the wheel speed detecting section 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 electric current in each wheel speed sensor circuit. If an open or short circuit in the wheel speed sensor circuit is detected, ASC-ECU sets a corresponding diagnostic trouble code.

PROBABLE CAUSES

Current trouble

Damaged wiring harness and connectors
Noise interference
Malfunction of wheel speed sensor
ASC-ECU malfunction

Past trouble

Carry out the diagnosis with a particular emphasis on the 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 Use Troubleshooting/Inspection Service Points ).

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

Using scan tool MB991958, 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 Diagnostics table ). On completion, go to Step 2.

STEP 2. DTC recheck after repairing the CAN bus line

Q. Is DTC C1020 set?

	Go to Step 3.

	This diagnosis is complete.

STEP 3. Scan tool service data

Check the following service data. (Refer to

Item No.03: RL wheel speed sensor

Q. Is the check result normal?

	Go to Step 10.

	Go to Step 4.

STEP 4. Connector check: Connector check: A-05 ASC-ECU connector, C-45 intermediate connector, D-18 wheel speed sensor <RL> connector

Q. Is the check result normal?

	Go to Step 5.

	Repair the defective connector. Then go to Step 11.

STEP 5. Voltage measurement at A-05 ASC-ECU connector

(1)Disconnect the ASC-ECU connector, connect the special tool ASC check harness (MB991997) to the wiring harness-side connector, and then measure 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 as well as between the ground terminal No. 37 and the body ground.
OK: 1 volt or less

Q. Is the check result normal?

YES

: Go to Step 6.

NO (Not normal at the terminal No. 34 or 33)

: Go to Step 8.

STEP 6. Resistance measurement at A-05 ASC-ECU connector

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

note

Do not connect the special tool to ASC-ECU.

(2)Measure the resistance between the wheel speed sensor circuit power supply terminal (signal terminal) No. 36 and the body ground as well as between the ground terminal No. 37 and the body ground.
OK: No continuity

Q. Is the check result normal?

YES

: Go to Step 7.

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

: Go to Step 8.

STEP 7. Voltage measurement at A-05 ASC-ECU connector

(1)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the ASC-ECU-side connector and the wiring harness-side connector, and then measure 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 and between the wheel speed sensor circuit ground terminal No. 37 and the body ground.
OK:
Terminal No.36 and the body ground: Battery positive voltage
Terminal No.37 and the body ground: 1 V or less

Q. Is the check result normal?

Go to Step 8.

Go to Step 10.

STEP 8. Check of wheel speed sensor as a single unit

Refer to

Q. Is the check result normal?

	Go to Step 9.

	Replace the wheel speed sensor <RL>. (Refer to .) Then go to Step 11.

STEP 9. Wiring harness check between A-05 ASC-ECU connector terminal No. 36 and D-18 wheel speed sensor <RL> connector terminal No. 1, and between A-05 ASC-ECU connector terminal No. 37 and D-18 wheel speed sensor <RL> connector terminal No. 2

Check for short or 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 11.

STEP 10. Check whether the DTC is reset.

(1)Erase the DTC.

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

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?

	Replace the hydraulic unit (incorporates in ASC-ECU).(Refer to .) Then go to Step 11.

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

STEP 11. Check whether the DTC is reset.

(1)Erase the DTC.

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

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?

	Return to Step 1.

	This diagnosis is complete.