Code No.C1542 Fail-safe relay stuck off


caution
  • If the electric power steering-ECU sets diagnosis code No.C1542, diagnose the CAN bus lines. If there is any fault in the CAN bus lines, an incorrect diagnosis code may be set.
  • Whenever the ECU is replaced, ensure that the communication circuit is normal.


DIAGNOSIS CODE SET CONDITIONS

  • Although the fail-safe relay (power relay) is turned on, the system is not energised and the microcomputer determines that the relay contact is open.
  • The fail-safe relay (power relay) is not turned on and the microcomputer determines that the relay contact is open.
    • Criteria for judging malfunction
    • Power supply voltage is less than 8 V and the difference between the ignition voltage and the power supply voltage is more than 2.5 V when the fail-safe relay is off.

PROBABLE CAUSES

  • Defective wire(s) or connector(s) in the power supply circuit to the electric power steering-ECU
  • Malfunction of the electric power steering-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III diagnosis code

caution Before connecting or disconnecting the M.U.T.-III, turn the ignition switch to the "LOCK" (OFF) position.
Check again if the diagnosis code is set.
(1)Turn the ignition switch to the "ON" position.
(2)Erase the diagnosis code.
(3)Turn the ignition switch to the "LOCK" (OFF) position.
(4)Turn the ignition switch to the "ON" position.
(5)Start the engine, and check the diagnosis code.
(6)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Are diagnosis codes C1542 and C1531 set simultaneously?

Go to Step 2.

Go to Step 4.

STEP 2. Check the motor wires of the steering gear and linkage assembly wiring harness for short to earth.

Disconnect electric power steering-ECU connector B-105-1 and measure the resistance.

  • Resistance between electric power steering-ECU connector B-105-1 terminal 31 and body earth
  • Resistance between electric power steering-ECU connector B-105-1 terminal 32 and body earth
OK: Open circuit or more than 300 Ω

Q. Is the check result normal?

Replace the steering gear box and linkage assembly (Refer to ).

Go to Step 3.

STEP 3. Check whether the diagnosis code is reset.

caution Before connecting or disconnecting the M.U.T.-III, turn the ignition switch to the "LOCK" (OFF) position.
Check again if the diagnosis code is set.
(1)Turn the ignition switch to the "ON" position.
(2)Erase the diagnosis code.
(3)Turn the ignition switch to the "LOCK" (OFF) position.
(4)Turn the ignition switch to the "ON" position.
(5)Check if the diagnosis code is set.
(6)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Are diagnosis codes C1542 and C1531 set?

Replace the electric power steering-ECU (Refer to ).

The malfunction is intermittent. Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction .

STEP 4. Check the motor wires of the steering gear and linkage assembly wiring harness for open circuit.

Disconnect electric power steering-ECU connector B-105-1 and measure the resistance.

  • Resistance between electric power steering-ECU connector B-105-1 terminals 31 and 32
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?

Go to Step 5.

Repair the harness connector and terminal, or replace the steering gear box and linkage assembly (Refer to ).

STEP 5. Check whether the diagnosis code is reset.

caution Before connecting or disconnecting the M.U.T.-III, turn the ignition switch to the "LOCK" (OFF) position.
Check again if the diagnosis code is set.
(1)Turn the ignition switch to the "ON" position.
(2)Erase the diagnosis code.
(3)Turn the ignition switch to the "LOCK" (OFF) position.
(4)Turn the ignition switch to the "ON" position.
(5)Start the engine.
(6)Check if the diagnosis code is set.
(7)Turn the ignition switch to the "LOCK" (OFF) position.
(8)Disconnect M.U.T.-III.

Q. Is diagnosis code C1542 set?

Replace the electric power steering-ECU (Refer to ).

The malfunction is intermittent. Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction .