Faulty power steering pressure sensor or switch giving an implausible or stuck signal; Damaged wiring, chafed insulation or poor connections in the sensor circuit (signal, reference or ground); Corroded or loose sensor connector, or fluid contamination of the plug; Low, aerated or degraded power steering fluid, or a worn pump causing abnormal pressure readings; Blocked or restricted power steering hose or fault in the steering rack affecting pressure; Fault in the engine control unit input circuit.

P0551

Power Steering Pressure Sensor/Switch Circuit Range/Performance.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
5: AreaVehicle speed, idle control and auxiliary inputs
51: FaultThe specific fault in that area

What it means

P0551 is the generic code for a range or performance fault in the power steering pressure sensor or switch circuit. The engine control unit compares the signal from the sensor or switch with what it expects, for example against steering input, engine load or vehicle speed, and sees a value that is implausible or does not change as it should. The sensor is used so the engine can raise idle speed or compensate for load when the steering is turned, so the main effects are on idle quality.

Symptoms

Engine warning light on
Rough, unstable or low idle when turning the steering, especially at parking speeds
Engine stalling or nearly stalling at full steering lock
Idle speed not rising when the steering is turned
Heavy or inconsistent steering feel if the hydraulic system is also at fault
Whining or groaning from the power steering pump

Possible causes

Faulty power steering pressure sensor or switch giving an implausible or stuck signallikely
Damaged wiring, chafed insulation or poor connections in the sensor circuit (signal, reference or ground)likely
Corroded or loose sensor connector, or fluid contamination of the pluglikely
Low, aerated or degraded power steering fluid, or a worn pump causing abnormal pressure readingspossible
Blocked or restricted power steering hose or fault in the steering rack affecting pressurepossible
Fault in the engine control unit input circuitrare

How to diagnose

Read and record the freeze frame data and check for any other stored codes, especially idle, sensor reference voltage or steering related ones
Check the power steering fluid level and condition, and look for leaks, foaming or contamination around the pump, hoses and sensor
Inspect the sensor, its connector and wiring for damage, chafing, corrosion, fluid ingress or heat damage
Using live data, watch the sensor reading or switch state with the engine idling and the steering centred, then turned slowly lock to lock, and check it responds as expected for your model
Check the sensor reference voltage, signal and ground at the connector with a multimeter against the manufacturer's specification
Test the wiring for continuity and short circuits between the sensor and the control unit
Check the pump and system pressure if the sensor and circuit test good, following the procedure for the specific vehicle
Clear the code and road test to see if it returns

How to fix

Replace the power steering pressure sensor or switch if it fails testing
Repair or replace damaged wiring and clean or renew corroded or damaged connector terminals
Top up or replace the power steering fluid with the correct specification and bleed air from the system
Repair or replace a worn pump, restricted hose or faulty steering rack if pressure is abnormal
Update or reflash the control unit software only if the manufacturer lists an outdated calibration as a known cause for this model

Can I keep driving?

Low severity

The car can normally be driven and booked in for repair soon. Take care at low speed and when parking, as the engine may stall or idle badly on full steering lock, and have it checked promptly if the steering feels heavy or the pump is noisy.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.