P0551 Code: Power Steering Pressure Sensor/Switch Circuit Range/Performance

What the P0551 code means

When you turn the steering wheel with the vehicle stopped, the hydraulic power steering pump loads the engine. The pressure sensor (or switch) warns the computer so it raises the idle a little and the engine does not stall.

The sensor gets a 5 V reference and a ground from the computer and returns a signal between about 0.5 and 4.5 V. A range or performance fault, which is what the P0551 code reports, means the sensor is reading but reading wrong, or that there is a real abnormal condition.

Without a good signal, the engine can stumble or stall when you turn the wheel all the way during maneuvers. Power steering fluid leaking out through the sensor itself is a frequent failure.

This kind of fault rarely shows up with a multimeter, because everything looks electrically correct. You have to compare what the part says against reality: with a gauge, a thermometer, a tachometer, or by commanding the component with the scan tool and seeing whether the physical result matches the command.

P0551 code symptoms

• Check engine light on.
• Idle that drops when you turn the wheel.
• The engine stalls or shakes when you turn the wheel while stopped.

Likely causes of the P0551 code

1. Degraded or out-of-calibration sensor. It gives believable readings that are wrong.
2. A real abnormal condition. The system really is running outside normal.
3. High resistance in the connector. Corrosion shifts the reading.
4. Damaged or blocked port, hose or reluctor wheel, depending on the type of sensor.

How to diagnose the P0551 code step by step

1. Read the sensor value on the scan tool and compare it with what you expect.
2. Inspect the connector for corrosion, water or loose pins.
3. Check the supply and ground with the key on: the reference should be correct, with less than 0.1 V of voltage drop on the ground.
4. Measure the signal with the connector plugged in and watch whether it changes with the condition.
5. Do a wiggle test on the harness with the scan tool in graph mode.
6. Check the continuity of each wire to the computer (under 1 ohm).

How to fix the P0551 code

• Repair the connector or the wiring.
• Replace the sensor if the tests confirm it is bad.
• Correct the real condition if there is one.
• Clear the codes and verify with a road test.

Technical reference data

• It can be a switch (2 wires) or a 5 V pressure sensor (3 wires).
• These values are a general guide: check the manufacturer data for your vehicle.

Brand-specific notes

This code is most common on vehicles with hydraulic power steering. Look for fluid leaking onto the sensor connector before you condemn the sensor.

P0551 on Nissan

Common on Nissan vehicles with hydraulic power steering.

P0551 on Honda

Common on Honda vehicles with hydraulic power steering.

P0551 on GM

Common on GM vehicles with hydraulic power steering.

Frequently asked questions about P0551