P055B
Engine Oil Pressure Sensor/Switch B Range/Performance.
- Generic
- Powertrain
- Generic code
- High severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 5
- AreaVehicle speed, idle control and auxiliary inputs
- 5B
- FaultThe specific fault in that area
What it means
P055B means the engine control unit has judged the signal from engine oil pressure sensor or switch 'B' to be implausible. The reading does not match what the ECU expects for the engine speed, load, temperature or other oil pressure sensor data. This can be a faulty sensor or wiring, or genuinely abnormal oil pressure. Which sensor is 'B' depends on the model and engine, so check manufacturer data.
Symptoms
- Oil pressure warning light on or flickering
- Engine management light on
- Oil pressure gauge reading erratically, too high or too low
- Engine running in a reduced-power or protection mode on some models
- Increased engine noise, such as ticking or rattling, if pressure is genuinely low
Possible causes
- Low engine oil level or oil in poor condition, such as diluted, degraded or the wrong gradelikely
- Faulty oil pressure sensor or switch B giving a drifting or stuck signallikely
- Damaged wiring, corroded connector or oil-soaked harness at the sensorpossible
- Genuinely low or high oil pressure due to a worn oil pump, blocked pickup strainer or pressure relief valve faultpossible
- Worn engine bearings causing low oil pressurerare
- Faulty variable-displacement oil pump control or its solenoid, on engines that have onerare
- ECU fault or outdated software, only where the manufacturer lists it as a known causerare
How to diagnose
- Check the oil level and condition on level ground, and look for fuel or coolant contamination or the wrong grade.
- Read the stored codes and freeze frame data, noting engine speed, temperature and load when the fault set, and check for related oil pressure or oil level codes.
- Inspect the sensor, its connector and the harness for oil contamination, chafing, corrosion, bent pins and leaks around the sensor.
- Check the live sensor data against the other oil pressure sensor, if fitted, at key on, engine off, and again at idle and higher revs.
- Check the sensor supply voltage, ground and signal wiring against the manufacturer's wiring data.
- Measure actual oil pressure with a mechanical gauge in place of the sensor, and compare it with the manufacturer's specification.
- If pressure is correct, test or substitute the sensor as per manufacturer procedure; if pressure is wrong, investigate the oil pump, strainer, relief valve and engine wear.
- Check for technical service bulletins or software updates for the vehicle, as the sensor layout varies by model and engine.
How to fix
- Correct the oil level and change the oil and filter using the specified grade if it is low, contaminated or wrong.
- Replace the faulty oil pressure sensor or switch, and clean the mounting area.
- Repair or replace damaged wiring and connectors, and clear any oil contamination in the harness.
- Repair the oil pump, clean or replace the pickup strainer, or replace the relief valve if mechanical pressure is out of specification.
- Carry out engine repairs if bearing wear is confirmed.
- Apply a manufacturer software update only if one is documented for this fault.
Can I keep driving?
Do not carry on driving until the oil level is checked and the oil pressure warning light is off. If the warning light stays on or the engine is noisy, stop and have the car recovered, as genuinely low oil pressure can quickly destroy the engine.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.