P051A

What it means

P051A means the engine control unit has detected a fault in the circuit of crankcase pressure sensor A, which monitors pressure inside the crankcase as part of the ventilation system. The fault is set when the sensor signal or supply is missing, out of range or electrically implausible. Sensor location, signal type and how the strategy is used depend on the engine and model.

Symptoms

• Engine management light on
• Possible rough idle or uneven running on some engines
• Oil leaks from seals or gaskets if crankcase pressure is genuinely high
• Oil smoke or oily residue around the breather system
• Other ventilation or emissions-related fault codes stored alongside

Possible causes

• Damaged, corroded or loose wiring or connector at the crankcase pressure sensorlikely
• Faulty crankcase pressure sensorlikely
• Open circuit, short to earth or short to supply in the signal, reference or earth wirepossible
• Oil contamination or blockage of the sensor port or its connecting hosepossible
• Fault in the crankcase ventilation system (blocked or disconnected breather, damaged hose) affecting the readingpossible
• Engine control unit internal fault or outdated softwarerare

How to diagnose

1. Read all stored codes and freeze frame data, noting engine temperature, load and speed when the fault set, and check for related ventilation or sensor supply codes.
2. Visually inspect the sensor, its connector, wiring and nearby hoses for damage, oil ingress, chafing, heat damage or corrosion.
3. Check the sensor port and any connecting pipe or hose for blockage, oil sludge, cracks or disconnection.
4. With the engine running, view live crankcase pressure data and compare it with the manufacturer's expected values; check it responds plausibly to engine speed and load.
5. Test the sensor reference supply and earth at the connector against the manufacturer's wiring data.
6. Check the signal wire for continuity, and for shorts to earth or supply, with the control unit and sensor disconnected.
7. Inspect the crankcase ventilation system for blockage, restricted or leaking components as the model specifies.
8. If the wiring and sensor tests are good, check for software updates and consider control unit testing as a last step.

How to fix

• Repair or replace damaged wiring and clean or replace corroded or loose connectors.
• Replace the crankcase pressure sensor if it is faulty or oil-contaminated.
• Clear blockages and replace damaged or disconnected breather hoses and ventilation components.
• Repair the supply, earth or signal circuit faults found during testing.
• Apply a manufacturer software update only if an outdated calibration is a known cause for that model, or repair or replace the control unit if it is confirmed faulty.

Can I keep driving?

Nearby codes

• P0519GenericIdle Air Control System Performance
• P051BGenericCrankcase Pressure Sensor A Circuit Range/Performance