Code No.C1206: Wheel speed sensor (FL) (short circuit)

caution

If there is any problem in the CAN bus lines, an incorrect diagnosis code may be set. Prior to this diagnosis, diagnose the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table ).
Before replacing the ECU, ensure that the communication circuit is normal.

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 ASTC-ECU.
The hydraulic unit assembly (integrated with ASTC-ECU) modulates the amount of braking force individually applied to each wheel cylinder.

DIAGNOSIS CODE SET CONDITIONS

Diagnosis code No.C1206 is set if any abnormal voltage from the wheel speed sensor is detected without the outputs of the code No.C1205.

PROBABLE CAUSES

Current trouble

Damaged wiring harness and connectors
Teeth lack or clogging of the ABS rotor
Malfunction of the front hub assembly
Noise interference
Wheel speed sensor malfunction
ASTC-ECU malfunction

Past trouble

Carry out diagnosis with particular emphasis on wiring harness and connector failures between ASTC-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 PROCEDURE

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

Use M.U.T.-III 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 Diagnostics Table ). On completion, go to Step 2.

STEP 2. Diagnosis code recheck after resetting CAN bus lines

(1)Erase the diagnosis code.

(2)Drive the vehicle at 15 km/h or more.

note

The ABS warning lamp does not turn OFF in some cases unless the vehicle runs at 15 km/h or higher.

Q. Is the diagnosis code No.C1206 set?

	Go to Step 3.

	This diagnosis is complete.

STEP 3. M.U.T.-III diagnosis code

Check that the diagnosis code No.C1205 is also set.

Q. Is the diagnosis code No.C1205 also set?

	Perform the diagnosis for the diagnosis code No.C1205 (Refer to ).

	Go to Step 4.

STEP 4. Check for wheel speed sensor installation

Check how the front wheel speed sensor (LH) is installed correctly (Disconnection of front wheel speed sensor (LH), loose mounting bolt, etc.).

Q. Is the check result normal?

	Go to Step 5.

	Reinstall the front wheel speed sensor (LH) correctly (Refer to ). Then go to Step 12.

STEP 5. Check the front hub for looseness.

note

If the wheel bearing or front hub or axle shaft bearing are loose, the gap between the wheel speed sensor and ABS rotor may become excessive.
Check the front hub, which diagnosis code indicates, for looseness. (Refer to GROUP 26 - On-vehicle service - Wheel Bearing Axial Play Check ).

Q. Is the check result normal?

	Go to Step 6.

	Replace the front hub assembly (Refer to GROUP 26 - Front Axle Hub Assembly ). Then go to Step 12.

STEP 6. Check the ABS rotor.

Check the ABS rotor (FL), which diagnosis code indicates, for foreign material or deformation.

Q. Is the check result normal?

	Go to Step 7.

	If the ABS rotor (FL) is contaminated with foreign material, clean it. If the front hub assembly is deformed, replace it (Refer to GROUP 26 - Front Axle Hub Assembly ). Then go to Step 12.

STEP 7. Connector check: A-68 ASTC-ECU connector, A-121 front wheel speed sensor (LH) connector.

Q. Is the check result normal?

	Go to Step 8.

	Repair the defective connector. Then go to Step 12.

STEP 8. Resistance measurement at the A-68 ASTC-ECU connector

(1)Disconnect the connector A-68, and connect special tool ASC check harness (MB992159) to the wiring harness-side connector.

note

Do not connect special tool ASC check harness (MB992159) to the ASTC-ECU.

(2)Measure the resistance between the A-68 ASTC-ECU connector terminal No.29 and body earth.
OK: No continuity

Q. Is the check result normal?

Go to Step 11.

Go to Step 9.

STEP 9. Resistance measurement at A-121 front wheel speed sensor (LH) connector

(1)Disconnect the front wheel speed sensor (RH) connector, and measure the resistance at the harness connector side.

(2)Disconnect the A-68 ASTC-ECU connector.

(3)Measure the resistance between the front wheel speed sensor (LH) terminal No.1 and body earth and between the front wheel speed sensor (LH) terminal No.2 and body earth.
OK: No continuity

Q. Is the check result normal?

	Go to Step 10.

	Repair the harness wire between A-121 front wheel speed sensor (RH) connector terminal No.1 and A-68 ASTC-ECU connector terminal No.13, or between A-121 front wheel speed sensor (RH) connector terminal No.2 and A-68 ASTC-ECU connector terminal No.29. Then go to Step 12 .

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 front wheel speed sensor (LH) (Refer to ). Then go to Step 11.

STEP 11. Check whether the diagnosis code is reset.

(1)Erase the diagnosis code.

(2)Drive the vehicle at 15 km/h or more.

note

The ABS warning lamp does not turn OFF in some cases unless the vehicle runs at 15 km/h or higher.

Q. Is the diagnosis code No.C1206 set?

	Replace the hydraulic unit (integrated with ASTC-ECU) (Refer to ). Then go to Step 12.

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

STEP 12. Check whether the diagnosis code is reset.

(1)Erase the diagnosis code.

(2)Drive the vehicle at 15 km/h or more.

note

The ABS warning lamp does not turn OFF in some cases unless the vehicle runs at 15 km/h or higher.

Q. Is the diagnosis code No.C1206 set?

	Return to Step 1.

	This diagnosis is complete.