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 PCM (terminal 52) via the resistor in the 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 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 PCM checks whether the power steering pressure switch turns "OFF" or "ON" during driving.

DTC SET CONDITIONS

Check Area
- Engine coolant temperature is higher than 30° C (86° F).
- Intake air temperature is higher than -10° C (14° F).
- Barometric pressure is higher than 76 kPa (11 psi).
- Drive for 4 seconds or more with the engine speed at 2,500 r/min or more, the volumetric efficiency at 55 percent or more and the vehicle speed is 5 km/h (3.1 mph) or more. Stop the vehicle, lowering the vehicle speed to 1.5 km/h (0.93 mph). 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.
- PCM failed.

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

CAUTION: To prevent damage to the scan tool, turn the ignition switch "OFF" before connecting or disconnecting the scan tool.




STEP 1. Using scan tool MB991502, check data list 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 not within specifications, go to Step 2.

If within specifications, it can be assumed that this malfunction is intermittent. Refer to vehicle level Testing and Inspection.

STEP 2. Check the power steering pressure switch.
Refer to On-vehicle Service.

If correct, go to Step 3.

If incorrect, replace the power steering pressure switch. Then go to Step 6.

STEP 3. Check the circuit at the power steering pressure switch connector A-76.
1. Disconnect connector A-76 and measure at the harness side.
2. Turn the ignition switch "ON".




3. Measure voltage between terminal 1 and ground.
- Voltage should be approximately 12 volts (battery positive voltage).

4. Turn the ignition switch "OFF".
If not within specifications, go to Step 4.

If within specifications, repair or replace the power steering pressure switch connector. Refer to vehicle level Testing and Inspection. Then go to Step 6.







STEP 4. Check the harness wire between the power steering pressure switch connector A-76 and the PCM connector C-90.
If the wire between the power steering pressure switch connector A-76 and the PCM connector C-90 is not damaged, go to Step 5.

If the wire between the power steering pressure switch connector A-76 and the PCM connector C-90 is damaged, repair it. Then go to Step 6.




STEP 5. Check harness connector C-90 at the PCM for damage.
If harness connector C-90 is damaged, repair or replace it.

Refer to vehicle level Testing and Inspection.

If harness connector C-90 is in good condition, replace the PCM.

Then go to Step 6.

CAUTION: To prevent damage to the scan tool, turn the ignition switch "OFF" before connecting or disconnecting the scan tool.




STEP 6. Using scan tool MB991502, check data list item 27: Power Steering Pressure Switch.
Check that the MUT-II display is "OFF" when the steering wheel is stopped, and that the display is "ON" when the steering wheel is steered in the idling state.