Power Steering Pressure Sensor/Switch Circuit
The Powertrain Control Module (PCM) uses the Power Steering Pressure (PSP) sensor to monitor hydraulic load and adjust engine idle speed accordingly. Code P0550 is set when the PCM detects an electrical signal from the PSP sensor circuit that falls outside the expected normal operating range.
This code is generally not a safety hazard and will not strand you. However, it can cause the engine to stall during low-speed parking maneuvers, so it should be addressed at your earliest convenience.
Common symptoms
- Illuminated Check Engine Light
- Engine RPM drops significantly when turning the steering wheel at a stop
- Engine stalling during low-speed parking maneuvers
- Rough or erratic engine idle
- Power steering fluid leaking from the sensor area
Likely causes
- Faulty power steering pressure (PSP) sensor
- Corroded, damaged, or loose wiring and connectors in the PSP sensor circuit
- Power steering fluid leak contaminating the sensor connector
- Low power steering fluid level causing erratic pressure readings
- Failed Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Check the power steering fluid level and condition.
Look for: Low fluid levels or heavily degraded fluid can cause erratic pressure spikes, leading to sensor circuit codes.
Visually inspect the PSP sensor, wiring harness, and connector.
Look for: Look for frayed wires, melted insulation, corrosion inside the connector, or power steering fluid leaking directly through the sensor into the electrical pins.
Verify the 5-volt reference and ground at the sensor connector using a multimeter.
Look for: With the key on and engine off, the reference wire should show approximately 5 volts and the ground should have good continuity. Missing voltage indicates a wiring or PCM issue.
Test the PSP sensor signal voltage while turning the steering wheel.
Look for: Back-probe the signal wire with the engine running; the voltage should change smoothly as you turn the wheel and increase hydraulic pressure. A static or out-of-range voltage indicates a failed sensor.
Check for continuity between the sensor connector and the PCM.
Look for: High resistance or an open circuit on the signal wire indicates a break in the wiring harness that needs to be repaired.
This page explains the generic P0550 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
Gear guide: Best OBD2 ScannersRead this code yourself next time — from $20 Bluetooth dongles to bidirectional scan tools.Rather have a pro handle it? Find a vetted local mechanic.