DTC P0551: Power Steering Pressure Switch Circuit Range/Performance

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.
  

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 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)

• Not applicable
  

• Engine coolant temperature sensor
  

DTC SET CONDITIONS

• Engine coolant temperature is higher than 20°C (68°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 (1.0 mph) or less]. Repeat 10 times or more.
  

• 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.
  

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 83, Power Steering Pressure Switch. If the steering wheel is not turned while idling, "OFF" will be displayed. If the steering wheel is turned while idling, "ON" will be displayed. (4)Turn the ignition switch to the "LOCK" (OFF) position. Q. Is the switch operating properly? It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions . Go to Step 2.

(3)Measure the voltage between terminal No. 1 and ground by backprobing. When steering wheel is not turned, 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? Go to Step 3. Go to Step 5.

	Go to Step 4.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 13.

	It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions .

	Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP 42B, ID Code Registration Necessity Judgment Table <Vehicles with KOS> or GROUP 42C, ID Codes Registration Judgment Table <Vehicles with WCM> . Then go to Step 13.

	Go to Step 6.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 13.

(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? Go to Step 10. Go to Step 7.

	Go to Step 8.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 13.

(1)Disconnect all ECM connectors. Connect the power plant ECU check harness special tool MB992110 between the separated connectors. (2)Disconnect the power steering pressure switch connector B-17. (3)Turn the ignition switch to the "ON" position.

(4)Measure the voltage between terminal No. 58 and ground. 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? Repair harness wire between power steering pressure switch connector B-17 (terminal No. 1) and ECM connector B-108 (terminal No. 58) because of open circuit. Then go to Step 13. Go to Step 9.

	Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP 42B, ID Code Registration Necessity Judgment Table <Vehicles with KOS> or GROUP 42C, ID Codes Registration Judgment Table <Vehicles with WCM> . Then go to Step 13.

	Repair it. Then go to Step 13.

	Go to Step 11.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 13.

	Go to Step 12.

	Repair it. Then go to Step 13.

	Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP 42B, ID Code Registration Necessity Judgment Table <Vehicles with KOS> or GROUP 42C, ID Codes Registration Judgment Table <Vehicles with WCM> . Then go to Step 13.

	The inspection is complete.

	The inspection is complete.

	Retry the troubleshooting.