P0551
Power Steering Pressure Sensor Circuit Range/PerformanceP0551 is a generic OBD-II powertrain diagnostic trouble code: Power Steering Pressure Sensor Circuit Range/Performance. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0551 means
P0551 is set when the PCM/ECM detects that the voltage or frequency signal from the power steering pressure (PSP) sensor is outside the expected range for the current operating conditions — that is, the signal is present and within electrical bounds but inconsistent with what the module expects given engine speed and steering input. The PSP sensor monitors hydraulic pressure in the power steering system and feeds this data to the PCM so it can raise idle speed when heavy steering loads are detected, preventing stalling during low-speed parking manoeuvres.
When P0551 is active, the PCM may ignore PSP input and stop compensating idle speed for steering load. This can lead to a rough or dropping idle when the steering wheel is turned to full lock, and in some cases the engine may stall. On vehicles where the PSP signal also feeds into the traction control or stability system, those functions may be degraded as well.
Common root causes include a failing PSP sensor that produces an erratic or stuck signal, low power steering fluid level that causes abnormal pressure readings, a worn or failing power steering pump generating inconsistent pressure, and wiring or connector faults in the sensor circuit. Because this is a range/performance code rather than a simple open/short, a scan tool with live data is essential to observe how the sensor behaves under actual steering loads.
Common causes
Most-frequently reported root causes when P0551 is logged.
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1
Faulty power steering pressure sensor producing an erratic or stuck-in-range signal.
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2
Low power steering fluid level causing abnormal or intermittent hydraulic pressure.
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3
Worn or failing power steering pump generating inconsistent pressure output.
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4
Damaged, corroded, or loose wiring connector at the PSP sensor.
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5
Chafed or intermittently open/shorted signal wire in the PSP sensor harness.
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6
Air in the power steering hydraulic circuit causing erratic pressure readings.
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7
Failed PCM input circuit for the PSP signal (rare).
Symptoms drivers notice
How to diagnose P0551
A typical diagnostic flow when this code is present.
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1
Connect an OBD-II scanner, record all stored codes and freeze frame data, and note any companion codes related to the power steering or idle system.
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2
Check the power steering fluid level and condition; top up to the correct level and inspect for leaks before proceeding.
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3
With the scanner displaying live PSP sensor data, observe voltage or pressure readings at idle versus at full steering lock; a signal that does not change with steering input indicates a faulty sensor or open wiring.
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4
Inspect the PSP sensor connector and harness for corrosion, bent pins, chafed insulation, or loose fit; repair any faults found.
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5
Use a digital multimeter to verify the sensor's 5-volt reference, signal, and ground circuits match the service manual specifications at the connector.
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6
If wiring checks pass, replace the PSP sensor with an OEM or OEM-equivalent part.
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7
Clear the code, test-drive with several full-lock steering manoeuvres, and confirm the code does not return and idle compensation is functioning correctly.
Related powertrain codes
Frequently asked questions
Can P0551 cause my engine to stall?
Yes. The PCM uses the PSP signal to raise idle speed when the power steering pump loads the engine at full steering lock. If the signal is lost or erratic, the idle compensation may not activate and the engine can stall, especially on vehicles with marginal base idle calibration.
Is P0551 specific to hydraulic power steering, or does it apply to electric power steering too?
P0551 applies to vehicles equipped with a hydraulic power steering pressure sensor. Vehicles with fully electric power steering (EPAS) typically do not have a PSP sensor and will not set this code.
Can low power steering fluid cause P0551 without a faulty sensor?
Yes. A low fluid level or air in the system can cause the hydraulic pressure to behave erratically, producing sensor readings that are out of the expected performance range and triggering P0551 even with a perfectly functional sensor.
How urgent is it to fix P0551?
It is moderately urgent. The vehicle remains driveable in most cases, but the stalling risk during parking manoeuvres and the potential for degraded stability control make it worth addressing within a few days rather than deferring indefinitely.
Disabling P0551 in software
RaceTune can permanently disable P0551 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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