P0550 means the engine control module detected a malfunction in the power steering pressure (PSP) sensor or switch circuit that it does not classify further. The specific members of the family are P0551 (range or performance), P0552 (low), P0553 (high) and P0554 (intermittent). Some manufacturers use only P0550 for any fault on the circuit; others reserve it for a signal that is present but contradicts other inputs, such as pressure reported with the engine off.
Severity: low. Can you keep driving? Yes. Hydraulic power steering works regardless of this signal. The engine computer uses it to raise idle when the pump loads the engine at low speed, so the symptom is a stumble or stall while turning the wheel at idle, or a high idle, with the check engine light on. On vehicles with electric steering the same code can come from the steering module's load message, with the same idle symptoms.
Why an engine code names the steering
A hydraulic pump at full lock can take several horsepower and pull a small engine's idle down far enough to stall it. The PSP device on the pump or the high-pressure line warns the module before that happens, so it can add air or throttle. That is the circuit's entire purpose, which is why a steering sensor lives in the powertrain code list.
Switch or sensor
Two wires means a switch that closes or opens at a set pressure; the module sees a high or low state. Three wires means a sensor with a 5-volt reference, a ground and a signal that rises with pressure. The test differs, and the scan tool's definition ("sensor/switch") does not say which the vehicle has. Look at the connector.
Causes, in the order they are found
The switch or sensor itself, leaking power steering fluid into its own connector or failed internally. Fluid on the device body or inside the connector is a diagnosis on its own.
A connector contaminated with fluid or with a terminal that has lost tension.
A wire chafed or broken in the harness near the pump, the belt and the brackets the harness crosses.
A ground with resistance, on designs where the switch grounds through the harness rather than through its threads.
A weak pump or low fluid on switch designs, when the pump cannot reach the switch's pressure and the module sees a state that never changes.
The module, last.
A diagnostic order that turns a general code into a specific one
- Record the freeze frame and companion codes. Idle control codes beside it confirm the symptom path.
- Check fluid level and look for leaks above the device.
- Open the connector and look for fluid, corrosion and loose terminals.
- For a switch, key on, unplugged: the signal wire should read the module's pull-up voltage (several volts). Then measure across the switch pins: open with the engine off, and the opposite state with the engine running and the wheel turned to a lock (the manual states which way the switch works).
- For a sensor, key on, unplugged: about 5 V on the reference, near 5 V on the signal, under 0.1 V of drop on the ground. Plug it back in and watch the signal live: it should rise smoothly as the wheel is turned to a lock at idle.
- Wiggle-test the harness with the engine running and the parameter on the scan tool.
- Replace the device only after the wiring passes, then clear and verify lock to lock at idle several times. Let the readiness monitors complete before an inspection.
Frequently asked questions
Can I drive with a P0550 code?
Yes. Power steering assist does not depend on this signal. Expect a stumble or stall when turning the wheel at idle, or a high idle, and the check engine light. Fix it to avoid stalling at low speed, but it is not a safety fault.
What is the difference between P0550 and P0552?
P0552 means the module classified the fault as a signal too low. P0550 means it found a fault it did not classify, or a reading that contradicts other data. The tests are the same; P0550 simply gives less of a hint about which wire.
Is P0550 the power steering pump?
Rarely. The switch or sensor, fluid in its connector, or a damaged wire account for most cases. A pump is suspected only when fluid is full, the device and wiring test good, and the pump cannot build the pressure a switch needs.
How much does it cost to fix P0550?
A power steering pressure switch or sensor is an inexpensive part with a short replacement and a fluid top-up. A connector or wire repair is similar. The pump is last on the list.
Related codes
- P0551: range or performance. P0552: low; see P0552. P0553: high. P0554: intermittent; see P0554.
- P0505 to P0507: idle control system codes, the symptom side; see P0507.
The code number itself tells you the family and the domain; how to read an OBD2 code number explains what each character means.