P055D
Engine Oil Pressure Sensor/Switch B High.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 5
- AreaVehicle speed, idle control and auxiliary inputs
- 5D
- FaultThe specific fault in that area
What it means
P055D means the engine control unit has seen the signal from engine oil pressure sensor or switch 'B' reading higher than expected, either as a high circuit voltage or as an implausibly high oil pressure. Which sensor is 'B', and the exact limits that set the code, depend on the model and engine. The fault can be electrical (sensor, wiring, supply or reference voltage) or a genuine oil pressure problem, so both must be checked.
Symptoms
- Engine management light on with P055D stored
- Oil pressure warning light on, flickering or showing wrongly
- Oil pressure gauge reading very high, pegged or erratic
- Reduced engine performance or limp mode on some models
- Variable oil pump or variable valve timing behaving oddly on engines that use the signal
- No noticeable symptoms other than the warning light
Possible causes
- Faulty oil pressure sensor or switch 'B' giving a false high signallikely
- Signal wire shorted to a voltage supply, or damaged wiring and connector pinslikely
- Open circuit in the ground or sensor return, causing the signal to read highpossible
- Genuinely high oil pressure from a stuck pressure relief valve or faulty oil pressure control valvepossible
- Wrong oil grade or very thick oil, especially when coldpossible
- Faulty engine control unit or sensor reference supplyrare
- Oil contamination or blocked oil gallery near the sensor affecting the readingrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting engine temperature, speed and load when the code set, and check for other oil or sensor supply codes.
- Check the oil level and condition, and confirm the oil grade matches the manufacturer's specification.
- Inspect the sensor, its connector and the wiring for oil contamination, chafing, bent or corroded pins, and heat damage.
- With the engine off, check the sensor's reference voltage, ground and signal at the connector against the model-specific wiring diagram.
- Watch the live oil pressure or sensor voltage data at key on, at idle and when revving, and see whether it stays high or changes with engine speed.
- Test for a short to voltage or an open ground by wiggling the harness and checking continuity and insulation between the sensor and control unit.
- Check actual oil pressure with a mechanical gauge to tell a sensor fault from a real pressure fault.
- If pressure is genuinely high, inspect the pressure relief valve and any oil pressure control valve or variable pump control, following the model's procedure.
How to fix
- Replace the oil pressure sensor or switch if it reads high against a verified mechanical pressure reading.
- Repair or replace damaged wiring, connectors or terminals, and clean off any oil contamination.
- Restore a faulty ground or reference supply circuit as the wiring diagram requires.
- Replace a stuck pressure relief valve or faulty oil pressure control valve, or repair the oil pump, if actual pressure is too high.
- Drain and refill with the correct grade and quantity of oil and a new filter if the oil is wrong or degraded.
- Clear the code and road test, confirming the sensor reading is plausible and the code does not return.
Can I keep driving?
If the oil warning light is off, the engine sounds normal and the gauge reading is sensible, the car can be driven gently for a short time while you arrange a repair. Stop and have it checked if the oil pressure warning light stays on, there are unusual engine noises, or it goes into limp mode.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.