Inspection Procedure 3

Inspection Procedure 3: The steering has become heavy, but electric power steering warning display does not illuminate.
(Power supply voltage assist fall)

COMMENTS ON TROUBLE SYMPTOM

Intermittent failure may be present in the power supply system. Check the battery and the generator to confirm that normal direct voltage flows.

PROBABLE CAUSES

- Malfunction of CAN bus line

- Defective battery

- Charging system failed

- Malfunction of the electric power steering-ECU

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 (Vehicles with CAN communication system)

STEP 1. Using scan tool MB991958, diagnose the CAN bus lines.

Use scan tool to diagnose the CAN bus lines.

Q. Is the check result normal?

YES Go to Step 2.
NO Repair the CAN bus lines CAN Bus Diagnostics Chart).
STEP 2. Using scan tool MB991958, check the data list

Check the following data list Data List Reference Table.

- Item No. B11: Odometer :rec.V1

- Item No. B12: Power relay voltage :rec V1

- Item No. B13: Vehicle speed :rec.V1

- Item No. B21: Odometer :rec.V2

- Item No. B22: Power relay voltage :rec V2

- Item No. B23: Vehicle speed :rec.V2

- Item No. B31: Odometer :rec.V3

- Item No. B32: Power relay voltage :rec V3

- Item No. B33: Vehicle speed :rec.V3

- Item No. B41: Odometer :rec.V4

- Item No. B42: Power relay voltage :rec V4

- Item No. B43: Vehicle speed :rec.V4

- Item No. B51: Odometer :rec.V5

- Item No. B52: Power relay voltage :rec V5

- Item No. B53: Vehicle speed :rec.V5

Q. Is the check result normal?

YES Go to Step 3.
NO Check the combination meter and repair if necessary Removal and Replacement). Then go to Step 5.
STEP 3. Check the battery voltage.

Start the engine and measure the battery voltage Battery Test).

Q. Is the check result normal?

YES Go to Step 4.
NO Check the battery and repair if necessary Procedures, Battery Removal and Replacement).
STEP 4. Check the charging system.

Start the engine and measure the charging system Generator Output Line Voltage Drop Test).

Q. Is the check result normal?

YES Go to Step 5.
NO Check the charging system and repair if necessary Removal and Replacement).
STEP 5. Retest the system

Q. Is the check result normal?

YES Intermittent malfunction How to Cope With Intermittent Malfunctions).
NO Replace the electric power steering-ECU (Refer to Service and Repair).