P0551

DTC P0551: Power Steering Pressure Sensor Circuit Range/Performance

Power Steering Pressure Switch Circuit:

CIRCUIT OPERATION
- A battery positive voltage is applied to the power steering pressure switch output terminal (terminal No.1) from the ECM (terminal No.54) via the resistor in the ECM.

TECHNICAL DESCRIPTION
- 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 volt and 12 volts.
- 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.

DESCRIPTIONS OF MONITOR METHODS
- Power steering pressure switch stays on during specified go/stop operations.

MONITOR EXECUTION
- Continuous

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
- Not applicable

Sensor (The sensor below is determined to be normal)
- Engine coolant temperature sensor

DTC SET CONDITIONS

Logic Flow Chart:

Logic Flow Chart

Check Conditions
- Engine coolant temperature is higher than 62 degrees C (144 degrees F).
- Drive for 4 seconds or more with the vehicle speed is 50 km/h (31 mph) or more. Stop the vehicle [vehicle speed is 1.5 km/h (1 mph) or less]. Repeat 10 times or more.

Judgment Criterion
- Power steering pressure switch continues to be "ON".

OBD-II DRIVE CYCLE PATTERN
None.

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Power steering pressure switch failed.
- Open or shorted power steering pressure switch circuit, harness damage, or connector damage.
- ECM failed.

DIAGNOSIS

Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991911: Main Harness B

STEP 1. Using scan tool MB991958, check data list item 27: Power Steering Pressure Switch.

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. Start the engine and run at idle.
3. Set scan tool MB991958 to the data reading mode for item 27, Power Steering Pressure Switch.
- If the steering wheel is stopped while idling, "OFF" will be displayed.
- If the steering wheel is steered while idling, "ON" will be displayed.

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

Q: Is the sensor operating properly?

YES: It can be assumed that this malfunction is intermittent.

NO: Go to Step 2.

STEP 2. Measure the power supply voltage at power steering pressure switch connector A-40 by backprobing.

1. Do not disconnect connector A-40.
2. Start the engine and run at idle.

3. Measure the voltage between terminal No.1 and ground by backprobing.
- When steering wheel is stationary, voltage should be battery positive voltage.
- When steering wheel is turned, voltage should be 1 volt or less.
4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the measured voltage within the specified range?

YES: Go to Step 3.

NO: Go to Step 5.

STEP 3. Check harness connector A-40 at power steering pressure switch for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 4.

NO: Repair or replace it. Then go to Step 14.

STEP 4. Using scan tool MB991958, check data list item 27: Power Steering Pressure Switch.

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.

STEP 5. Check harness connector A-40 at power steering pressure switch for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 6.

NO: Repair or replace it. Then go to Step 14.

STEP 6. Measure the power supply voltage at power steering pressure switch harness side connector A-40.

1. Disconnect connector A-40 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 volts) present?

YES: Go to Step 11.

NO: Go to Step 7.

STEP 7. Measure the power supply voltage at ECM connector C-119 by backprobing.

1. Do not disconnect the ECM connector C-119.
2. Disconnect the power steering pressure switch connector B-116.
3. Turn the ignition switch to the "ON" position.

4. Measure the voltage between terminal No.54 and ground by backprobing.
- Voltage should be between battery positive voltage.

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

Q: Is battery positive voltage (approximately 12 volts) present?

YES: Go to Step 8.

NO: Go to Step 9.

STEP 8. Check harness connector C-119 at ECM for damage.

Q: Is the harness connector in good condition?

YES: Check harness connector A-13 at the intermediate connector for damage, and repair or replace as required. If the intermediate connector is in good condition, repair the harness wire between power steering pressure switch connector A-40 (terminal No.1) and ECM connector C-119 (terminal No.54) because of open circuit. Then go to Step 14.

NO: Repair or replace it. Then go to Step 14.

STEP 9. Check harness connector C-119 at ECM for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 10.

NO: Repair or replace it. Then go to Step 14.

STEP 10. Check for short circuit to ground between power steering pressure switch connector A-40 (terminal No.1) and ECM connector C-119 (terminal No.54).

NOTE: Check the harness after checking intermediate connector A-13. If the intermediate connector is damaged, repair or replace it. Then go to Step 14.

Q: Is the harness wire in good condition?

YES: Replace the ECM. Then go to Step 14.

NO: Repair it. Then go to Step 14.

STEP 11. Replace the power steering pressure switch.

1. Replace the power steering pressure switch.
2. Retest the system.
3. Check the diagnostic trouble code (DTC).

Q: Is DTC P0551 set?

YES: Go to Step 12.

NO: Go to Step 14.

STEP 12. Check harness connector C-119 at ECM for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 13.

NO: Repair or replace it. Then go to Step 14.

STEP 13. Check for harness damage between power steering pressure switch connector A-40 (terminal No.1) and ECM connector C-119 (terminal No.54).

NOTE: Check the harness after checking the intermediate connector A-13. If the intermediate connector is damaged, repair or replace it. Then go to Step 14.

Q: Is the harness wire in good condition?

YES: Replace the ECM. Then go to Step 14.

NO: Repair it. Then go to Step 14.

STEP 14. Using scan tool MB991958, check data list item 27: Power Steering Pressure Switch.

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. Start the engine and run at idle.
3. Set scan tool MB991958 to the data reading mode for item 27, Power Steering Pressure Switch.
- If the steering wheel is stopped while idling, "OFF" will be displayed.
- If the steering wheel is steered while idling, "ON" will be displayed.

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

Q: Is the switch operating properly?

YES: The inspection is complete.

NO: Retry the troubleshooting.