Inspection Procedure 29

Inspection procedure 29: Power steering pressure switch system














CIRCUIT OPERATION

- A battery positive voltage is applied to the power steering pressure switch output terminal (terminal No. 1) from the ECM (terminal No. 58) via the resistor in the ECM.

COMMENT

- The power steering pressure switch converts the existence of a power steering load into a high/low voltage, and inputs it into the ECM.

- When the steering wheel is turned, hydraulic pressure rises. The power steering pressure switch closes, and the applied battery positive voltage will be grounded. With this, the power steering pressure switch output voltage will fluctuate between 0 and 12 V.

- While driving with the steering wheel held straight, the power steering pressure switch turns "OFF".

- The ECM checks whether the power steering pressure switch turns "OFF" or "ON" during driving.

TROUBLESHOOTING HINTS (The most likely causes for this case:)

- Power steering pressure switch failed.

- Open power steering pressure switch circuit, harness damage or connector damage.

- ECM failed.

DIAGNOSIS

Required Special Tool:

- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.

- MB991827: USB Cable

- MB991910: Main Harness A

STEP 1. Using scan tool MB991958, read the diagnostic trouble code (DTC).





CAUTION:
To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK"
(OFF) position before connecting or disconnecting scan tool MB991958.

(1)Connect scan tool MB991958 to the data link connector.
(2)Turn the ignition switch to the "ON" position.
(3)Read the DTC.
(4)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is DTC P0551 set?

YES Refer to, DTC P0551 - Power Steering Pressure Switch Circuit Range/Performance P0551.

NO Go to Step 2.

STEP 2. Check harness connector B-17 at power steering pressure switch for damage.

Q. Is the harness connector in good condition?

YES Go to Step 3.
NO Repair or replace it. Harness Connector Inspection.
Then confirm that the malfunction symptom is eliminated.
STEP 3. Measure the power supply voltage at power steering pressure switch harness side connector B-17.

(1)Disconnect the connector B-17 and measure at the harness side.

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





(3)Measure the voltage between terminal No. 1 and ground.

- Voltage should be battery positive voltage.
(4)Turn
the ignition switch to the "LOCK" (OFF) position.

Q. Is battery positive voltage (approximately 12 V) present?

YES Go to Step 7.

NO Go to Step 4.

STEP 4. Check harness connector B-108 at ECM for damage.

Q. Is the harness connector in good condition?

YES Go to Step 5.
NO Repair or replace it. Harness Connector Inspection.
Then confirm that the malfunction symptom is eliminated.
STEP 5. Check for open circuit between power steering pressure switch connector B-17 (terminal No. 1) and ECM connector B-108 (terminal No. 58).

Q. Is the harness wire in good condition?

YES Go to Step 6.
NO Repair it. Then confirm that the malfunction symptom is eliminated.
STEP 6. Using scan tool MB991958, check data list item 83: Power Steering Pressure Switch.

(1)Start the engine and run at idle.

(2)Set scan tool MB991958 to the data reading mode for item 83, Power Steering Pressure Switch.

- If the steering wheel is not turned while idling, "OFF" should be displayed.

- If the steering wheel is turned while idling, "ON" should be displayed.

(3)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is the operating properly?

YES It can be assumed that this malfunction is intermittent. How to Cope With Intermittent Malfunctions.
NO Replace the ECM (Refer to, Removal and Installation Removal and Replacement).
Then confirm that the malfunction symptom is eliminated.
STEP 7. Check harness connector B-108 at ECM for damage.

Q. Is the harness connector in good condition?

YES Go to Step 8.
NO Repair or replace it. Harness Connector Inspection.
Then confirm that the malfunction symptom is eliminated.
STEP 8. Check for harness damage between power steering pressure switch connector B-17 (terminal No. 1) and ECM connector B-108 (terminal No. 58).

Q. Is the harness wire in good condition?

YES Replace the power steering pressure switch. Then confirm that the malfunction symptom is eliminated.
NO Repair it. Then confirm that the malfunction symptom is eliminated.