P0551

Power Steering Pressure Switch Circuit:

CIRCUIT OPERATION
- A battery positive voltage is applied to the power steering pressure switch output terminal (terminal 1) from the ECM (terminal 54) or PCM (terminal 52) via the resistor in the ECM or PCM .

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 or PCM .
- 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 12 volts and 0 volt.
- While driving with the steering wheel held straight, the power steering pressure switch turns "OFF."
- The ECM or PCM checks whether the power steering pressure switch turns "OFF" or "ON" during driving.

DTC SET CONDITIONS

Check Conditions
- Intake air temperature is higher than -10°C (14°F).
- Barometric pressure is higher than 76 kPa (11 psi).
- Engine coolant temperature is higher than 30°C (86°F).
- Drive for two seconds or more with the engine speed at 2,500 r/min or more, the volumetric efficiency at 55 percent or more, and vehicle speed is 5 km/h (3.1 mph) or more. Stop the vehicle [vehicle speed is 1.5 km/h (0.93 mph) or less]. Repeat 10 times or more.

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

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, or loose connector.
- ECM failed.
- PCM failed.

DIAGNOSIS
Required Special Tool:
MB991502: Scan Tool (MUT-II)

CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.

STEP 1. Using scan tool MB991502, check data list item 27: Power Steering Pressure Switch.
1. Connect scan tool MB991502 to the data link connector.
2. Start the engine and run at idle.
3. Set scan tool MB991502 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.

If within specifications, this malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope With Intermittent Malfunction.

If not within specifications, go to Step 2.

STEP 2. Check the circuit at power steering pressure switch connector B-19.
1. Disconnect connector B-19 and measure at the harness side.
2. Turn the ignition switch to "ON" position.
3. Measure voltage between terminal 1 and ground.
- Voltage should be battery positive voltage.

4. Turn the ignition switch to "LOCK" (OFF) position. If within specifications, go to Step 3.

If not within specifications, check intermediate connector B-47 and repair or replace as required.
Refer to Harness Connector Inspection. If the intermediate connector B-47 is in good condition, go to Step 4.

STEP 3. Check harness connector B-19 at the power steering pressure switch for damage.
If harness connector B-19 is in good condition, replace the power steering pressure switch. Then go to Step 7.

If harness connector B-19 is damaged, repair or replace it.
Refer to Harness Connector Inspection. Then go to Step 7.

STEP 4. Check harness connector C-58 at the ECM or harness connector C-55 at the PCM for damage.
If harness connector C-58 or C-55 is in good condition, go to Step 5.

If harness connector C-58 or C-55 is damaged, repair or replace it. Refer to Harness Connector Inspection. Then go to Step 7.

STEP 5. Check the harness wire between power steering pressure switch connector B-19 and ECM connector C-58 or PCM connector C-55 .
If the wire between power steering pressure switch connector B-19 and ECM connector C-58 or PCM connector C-55 is not damaged, go to Step 6.

If the wire between power steering pressure switch connector B-19 and ECM connector C-58 or PCM connector C-55 is damaged, repair it. Then go to Step 7.

STEP 6. Check the power steering pressure switch.
Refer to On-vehicle Service - Power Steering Oil Pressure Switch Check.

If correct, replace the ECM or PCM. Then go to Step 7.

If incorrect, replace the power steering pressure switch. Then go to Step 7.

STEP 7. Test the OBD-II drive cycle.
1. Carry out a test drive with the drive cycle patter. Refer to Procedure 6 - Other Monitor.
2. Read the diagnostic trouble code, and confirm that diagnostic trouble code P0551 does not reset.