C1540

DTC C1540 Power supply voltage abnormality (high voltage)

CAUTION:

- If there is any problem in the CAN bus lines, an incorrect DTC may be set. Prior to this diagnosis, diagnose the CAN bus lines Scan Tool Testing and Procedures ).
- Whenever ECU is replaced, ensure that the CAN bus lines are normal.

OPERATION

- Power is supplied to the electric power steering-ECU from the battery or the ignition switch.

FUNCTION

- To control the steering gear and linkage assembly, the battery voltage is supplied to the electric power steering-ECU.

TROUBLE JUDGMENT

Judgment Criterion

- The power supply voltage is more than 17.5 V.
- The power supply monitor voltage does not meet a predetermined voltage stored in the microcomputer, and the microcomputer determines that there is a problem in the power supply system.

Fail Safe, Back Up Function

- The electric power steering-ECU stops the motor control and illuminates the electric power steering warning display, then sets the DTC C1540.

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 3.
NO Repair the CAN bus lines CAN Bus Diagnostics Chart). On completion, go to Step 2.
STEP 2. DTC recheck after resetting CAN bus lines

(1)Erase the DTC.

(2)Turn the ignition switch from the "LOCK" (OFF) position to the "ON" position.

(3)Check if the DTC is set.

Q. Is the DTC C1540 set?

YES Go to Step 3.
NO This diagnosis is complete.
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 Battery Charging, Battery Removal and Replacement). Then go to Step 7.
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). Then go to Step 7.
STEP 5. Using scan tool MB991958, check the data list

Check the following data list Data List Reference Table.

- Item No. 22: Power relay voltage

- Item No. 23: Ignition voltage

Q. Is the check result normal?

YES Go to Step 7.
NO Go to Step 6.
STEP 6. Check whether the DTC is reset.

(1)Erase the DTC.

(2)Turn the ignition switch from the "LOCK" (OFF) position to the "ON" position.

(3)Check if the DTC is set.

Q. Is the DTC C1540 set?

YES Replace the electric power steering-ECU (Refer to Service and Repair). Then go to Step 7.
NO Intermittent malfunction How to Cope With Intermittent Malfunctions).
STEP 7. Check whether the DTC is reset.

(1)Erase the DTC.

(2)Turn the ignition switch from the "LOCK" (OFF) position to the "ON" position.

(3)Check if the DTC is set.

Q. Is the DTC C1540 set?

YES Return to Step 1.
NO This diagnosis is complete.