Inspection Procedure 1: the Scan Tool Cannot Communicate With the ABS/ASC System.

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.
^ 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.

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: ASC-ECU Power Supply Circuit System.)
NO: Repair the CAN bus lines. (Refer to Troubleshooting Can Bus Diagnostics Table.)