Inspection Procedure 1

Inspection Procedure 1: The scan tool cannot communicate with the ABS/ASC system.

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 Initial Inspection and Diagnostic Overview ).
- Whenever the ECU is replaced, ensure that the CAN bus lines are normal.
- If the power is supplied with the ground circuit of CAN communication devices open circuited, a potential abnormality may occur to the connected CAN bus line.
- 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 G and Yaw Rate Sensor Calibration , Testing and Inspection , Master Cylinder Brake Fluid Pressure Sensor Calibration , and Testing and Inspection ).

TECHNICAL DESCRIPTION (COMMENT)

When the scan tool MB991958 cannot communicate with the ABS/ASC system, there may be a malfunction to the CAN bus lines, ASC-ECU power supply circuit, ground, or ASC-ECU.

PROBABLE CAUSES

- Damaged wiring harness and connectors
- ASC-ECU malfunction
- Wrong M.U.T.-III wiring harness
- Abnormality in battery or generator
- Abnormality in power supply voltage to ASC-ECU
- ECU malfunction of other system

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

Using scan tool MB991958, diagnose the CAN bus lines.

Using the scan tool, diagnose the CAN bus lines.

Q. Is the check result normal?

YES Check and repair the power supply circuit system (Refer to Inspection Procedure 11).
NO Repair the CAN bus lines CAN Bus Diagnostics Chart).