P0550 Code: Power Steering Pressure Sensor/Switch Circuit

What the P0550 code means

Turning the steering wheel while the vehicle is stopped demands a lot from the power steering pump, and the engine itself drives that pump. If nobody warned the engine, it would lose rpm every time the driver maneuvers to park.

That is why the power steering pressure sensor exists. Its job is to let the computer know the pump is working hard, so the computer raises the idle slightly and makes up for the load before you notice it.

The P0550 code is stored when that sensor does not deliver a valid signal. The characteristic symptom is unmistakable: the engine drops in rpm or stalls when you turn the wheel to the stop with the vehicle standing still, typically while parking.

It helps to tell this code apart from a real steering problem. Here the power steering keeps working: the pump runs and the wheel turns normally. What fails is the warning to the engine, so the symptom shows up in the engine and not in the steering.

It is worth telling two kinds of sensor apart, because the test changes. Some vehicles use a simple pressure switch, which has only two states and is checked by confirming that it flips when you turn the wheel to the stop. Others use an analog sensor that gives a proportional signal, and there you have to watch whether the voltage rises progressively with effort. Applying the wrong test gives a result that looks like a fault and is not.

P0550 code symptoms

• Drop in rpm when you turn the wheel with the vehicle stopped.
• The engine stalls when maneuvering to park.
• Check engine light on.
• Unsteady idle during maneuvers.
• The steering keeps assisting normally.
• The symptom gets worse with the air conditioning on.
• Possibly an idle that is a bit higher than normal all the time.
• On switch-type systems, the signal does not flip when you turn the wheel to the stop.

Likely causes of the P0550 code

1. Failed pressure sensor. The most frequent cause.
2. Connector that is corroded or has moisture, common because of where it sits in the engine compartment.
3. Wiring damaged by heat or rubbing.
4. Power steering fluid leaking onto the connector, which causes corrosion.
5. Low power steering fluid level.
6. Worn power steering pump, which does not build the expected pressure.
7. Poor ground in the circuit.
8. Loose accessory belt, which makes the pump slip.

How to diagnose the P0550 code step by step

1. Watch the sensor signal in live data while you turn the wheel. It should change clearly at the stops and return when you let go.
2. Check the power steering fluid level and condition. A low level changes the real pressure and produces the same symptom.
3. Inspect the connector for corrosion, moisture and traces of power steering fluid.
4. Look for leaks in the lines near the sensor.
5. Measure the sensor resistance or its signal voltage, depending on the type, and compare it with the specification.
6. Check the supply voltage and the ground of the circuit.
7. Check the accessory belt tension, because a loose belt makes the pump slip.
8. Listen to the pump at full lock. A loud, sustained whine points to wear or a lack of fluid.
9. Find out whether the sensor is a switch or an analog type before you test it. The first only flips between two states, and the second gives a signal proportional to effort.

How to fix the P0550 code

• Replace the pressure sensor when its signal does not change as you turn the wheel or it is out of specification.
• Clean or replace the corroded connector and protect it with dielectric grease.
• Repair power steering fluid leaks that wet the connector.
• Correct the fluid level using the manufacturer specification.
• Repair damaged wiring and route it away from hot areas.
• Tighten or replace the accessory belt if it slips.
• Replace the power steering pump if it does not build the expected pressure.
• Apply the test that matches the type of sensor installed, because the wrong method gives false diagnoses.

After the repair, check that the engine holds its idle when you turn the wheel to the stop with the vehicle standing still.

Technical reference data

• The sensor can be a two-state switch or an analog sensor, depending on the vehicle.
• On analog sensors, the signal usually moves between 0.5 and 4.5 volts depending on the pressure.
• The computer raises the idle by 50 to 200 rpm when it detects steering load.
• Typical power steering pump pressure at full lock: 70 to 100 bar (about 1,000 to 1,450 psi).
• The symptom gets worse with the air conditioning on, because it adds another load to the engine.
• Switch-type sensors: two states. Analog sensors: proportional signal between 0.5 and 4.5 volts.

Brand-specific notes

The symptom of this code is often mistaken for an idle or throttle body problem, because what the driver notices is that the engine stalls while maneuvering. The clue that separates them is the direct link to turning the wheel: if it happens only when you turn and not in other situations, look here before you chase the idle.

Power steering fluid leaking onto the connector is a frequent cause and easy to see. Before you order the sensor, check whether the connector is soaked: if it is, the leak has to be repaired too, or the new part will corrode just the same.

Frequently asked questions about P0550