Inspection Procedure 13: Steering Wheel Sensor Power Supply Circuit System

Inspection Procedure 13: Steering wheel sensor power supply circuit 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 (Refer to Trouble code diagnosis Can Bus Diagnostics Table).
^ Whenever ECU is replaced, ensure that the CAN bus lines are normal.
^ When the steering wheel sensor is replaced, always carry out calibration to make ASC-ECU learn the neutral point.

OPERATION
^ Steering wheel sensor contains the power supply circuit (terminal No.2) for Steering wheel sensor. The power is supplied from the ETACS-ECU (terminal No.5). The power is supplied from the fusible link No.33 through the multipurpose fuse No.12.
^ When malfunction occurs in Steering wheel sensor power supply, the communication with scan tool becomes unavailable.

PROBABLE CAUSES
^ Damaged wiring harness and connectors
^ Fuse and fusible link malfunction
^ Improper tightening of battery terminal
^ Battery failure
^ Charging system failed
^ Steering wheel sensor malfunction

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
^ MB991997: ASC check harness

STEP 1. Connector check: C-209 steering wheel sensor connector
Q: Is the check result normal?
YES: Go to Step 2.
NO: Repair the damaged connector.

STEP 2. Resistance measurement at C-209 steering wheel sensor connector.
1) Disconnect C-209 steering wheel sensor connector and measure the resistance available at the wiring harness side of the connector.
2) Check the continuity between C-209 steering wheel sensor connector terminal No.5 and body ground.
OK: Continuity exists (2 ohms or less)
Q: Is the check result normal?
YES: Go to Step 4.
NO: Go to Step 3.

STEP 3. Check the wiring harness between C-209 steering wheel sensor connector terminal No.5 and the body ground.
^ Check the ground wires for open circuit.
Q: Is the check result normal?
YES: If a trouble is solved, it is determined that there is an intermittent malfunction such as poor engaged connector(s) or open circuit.
NO: Repair the wiring harness.

STEP 4. Connector check: C-309 ETACS-ECU connector, C-317 ETACS-ECU connector
Q: Is the check result normal?
YES: Go to Step 5.
NO: Repair the damaged connector.

STEP 5. Voltage measurement at C-309 ETACS-ECU connector
1) Disconnect C-306 ETACS-ECU connector and measure the voltage available at the wiring harness side of the connector.
2) Measure the voltage between C-309 ETACS-ECU connector terminal No.1 and body ground.
OK: Battery positive voltage
Q: Is the check result normal?
YES: Go to Step 7.
NO: Go to Step 6.

STEP 6. Check the wiring harness between fusible link No. 34 and C-309 ETACS-ECU connector terminal No.1.
^ Check the power supply lines (battery power supply) for open circuit and short circuit.
Q: Is the check result normal?
YES: If a trouble is solved, it is determined that there is an intermittent malfunction such as poor engaged connector(s) or open circuit.
NO: Repair the wiring harness.

STEP 7. Measure the voltage at the C-209 steering wheel sensor connector.
1) Disconnect C-209 steering wheel sensor connector and measure the voltage at the wiring harness side of the connector.
2) Turn the ignition switch to the ON position.
3) Measure the voltage between the terminal No.2 and the body ground.
OK: Approximately battery positive voltage
Q: Is the check result normal?
YES: Go to Step 10.
NO: Go to Step 8.

STEP 8. Check the fuse No.12.
Visually check for open circuit in fuse No.12.
Q: Is the check result normal?
YES: Go to Step 9.
NO: The short circuit may be present in the power supply circuit. Check the wiring harness between the C-209 steering wheel sensor connector terminal No.2 and the C-317 ETACS-ECU connector terminal No.5, and repair if necessary. And then replace the fuse No.12.

STEP 9. Check the wiring harness between C-209 steering wheel sensor connector terminal No.2 and C-317 ETACS-ECU connector terminal No.5.
^ Check the power supply lines (battery power supply) for open circuit.
Q: Is the check result normal?
YES: Go to Step 10.
NO: Repair the wiring harness between the C-209 steering wheel sensor connector terminal No.2 and the C-317 ETACS-ECU connector terminal No.5.

STEP 10. Using scan tool MB991958, check the ETACS system data list
Check the input signal of IG1 relay.
^ Turn the ignition switch to the ON position.





OK: Normal condition is displayed.
Q: Is the check result normal?
YES: Replace the steering wheel sensor.
NO: Refer to ETACS -Input Signal Procedure 2 "The ignition switch (IG1) signal is not received." Inspection Procedure 1.