OBD-II Code P0551 — What It Means & How to Fix It

What Does This Error Mean?

P0551 means the power steering pressure sensor is giving readings outside the expected range or inconsistent with actual operating conditions. The PCM monitors power steering pressure so it can slightly increase idle speed when steering effort is high — this prevents the engine from stalling when the power steering pump puts a heavy load on the engine. When the sensor reads incorrectly, the PCM may not compensate properly, which can cause the engine to stumble or stall when turning at low speed.

Affected Models

Vehicles 1996 and newer with hydraulic power steering and a power steering pressure sensor
Common on GM, Ford, Chrysler, Toyota, Honda, and Nissan
Any vehicle where the power steering pump is belt-driven and connected to the engine
Front-wheel-drive vehicles where sharp low-speed turns create the most power steering load
Higher mileage vehicles where power steering pressure sensors have aged or corroded

Common Causes

Power steering pressure sensor has failed — giving out-of-range voltage output
Power steering fluid is low, causing erratic pressure that pushes sensor readings outside normal range
Sensor connector has corroded terminals causing erratic or biased signal
Air is trapped in the power steering system from a recent fluid service, causing unstable pressure
PCM reference voltage to the sensor has drifted, causing the sensor output to read incorrectly

How to Fix It

Check the power steering fluid level first. Low fluid level causes erratic pressure, which can trigger P0551. Top up the fluid to the proper level with the manufacturer-recommended type.

Do not mix different power steering fluid types. If you are unsure what fluid is in the system, flush and refill rather than just topping up.
Locate the power steering pressure sensor. It is typically on the high-pressure line between the power steering pump and the steering rack or steering box. It looks like a small threaded sensor with a single wire connector.

On some vehicles the sensor is on the pump itself. Check the service manual for the exact location.
Inspect the sensor connector for corrosion and a secure connection. Unplug it, clean with electrical contact cleaner, and reconnect. Clear the code and test — connector faults are a common cause of P0551.

Power steering pressure sensors are exposed to power steering fluid, which can wick into the connector and cause corrosion.
Use a scan tool to view power steering pressure sensor voltage in live data. With the engine idling straight ahead, compare the reading to what the system should produce at rest. Turn the steering wheel fully to one stop — pressure should increase significantly.

At rest (wheels straight, not turning), power steering pressure is typically low. At full lock, pressure is much higher — near the relief pressure limit of the pump.
Replace the sensor if the live data reading is abnormal and the fluid level and connector are fine. Remove the old sensor and install the new one hand-tight plus a quarter turn — do not overtighten. Replenish any fluid spilled and purge air by turning the wheel lock-to-lock several times.

Wrap the connector area with a rag before removing the sensor — power steering fluid sprays out under pressure if the engine is not cold.

When to Call a Professional

Power steering pressure sensor replacement is a DIY-friendly repair. The sensor threads into the high-pressure power steering line — a small amount of fluid will spill during replacement. A shop can handle this in under 1 hour in most cases.

Frequently Asked Questions

Will P0551 make my steering harder?

No — P0551 is a sensor monitoring issue, not a power steering failure. The hydraulic power steering system still works normally. The impact is on idle control — the PCM may not raise idle speed when you turn the wheel, which can cause a slight stumble or stall on sharp, slow turns.

What is the power steering pressure sensor for?

It tells the PCM when the power steering pump is under heavy load. When you turn the wheel at low speed, the pump works hard and places a significant load on the engine. The PCM uses the sensor reading to momentarily raise idle speed, preventing the engine from stalling under this extra load.

Do electric power steering cars have P0551?

No. Electric power steering (EPS) uses an electric motor, not a hydraulic pump. There is no hydraulic pressure to measure, so there is no power steering pressure sensor. P0551 is only relevant on vehicles with belt-driven hydraulic power steering pumps.