P051D

What it means

P051D means the engine control unit has seen the signal from crankcase pressure sensor 'A' sit higher than its expected electrical range. This is a circuit fault: the voltage on the signal wire is above the normal operating window. The sensor is used to monitor crankcase ventilation, and its exact location and the way it is monitored vary by make, model and engine.

Symptoms

• Engine management light on
• Possible rough or unstable idle on some engines
• Oil leaks or seepage at seals and gaskets if crankcase pressure is genuinely high
• Oil mist or whistling noises from the breather system
• Possible reduced performance if the engine control unit applies a fallback strategy
• No noticeable symptoms other than the warning light

Possible causes

• Wiring fault such as the signal wire shorted to a voltage supply or to the sensor reference feedlikely
• Open circuit in the sensor ground wire or a poor ground connection, which pulls the signal highlikely
• Faulty crankcase pressure sensorlikely
• Corroded, damaged or loose connector terminals at the sensor or control unitpossible
• Genuinely excessive crankcase pressure from a blocked, frozen or faulty ventilation system, or heavy blow-by, on systems that report this as a high faultpossible
• Fault inside the engine control unit, such as the sensor supply or input circuitrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data. Note engine speed, load and temperature when the fault set, and look for related sensor supply or ventilation codes.
2. Check for any manufacturer service information or software updates relating to this code for the specific model and engine.
3. Visually inspect the sensor, its wiring and connector for chafing, heat damage, oil contamination, corrosion and pushed-back pins.
4. View live crankcase pressure sensor data with the ignition on and the engine off, and check the reading is plausible. Compare it with the reading at idle.
5. Unplug the sensor and check the reference supply and ground against the wiring diagram. Look for a missing ground or a supply voltage on the signal wire.
6. Check the signal wire for a short to voltage and for continuity back to the control unit, with the connector unplugged at both ends.
7. Inspect the crankcase ventilation hoses, breather and separator for blockage, collapse, ice or damage, and check for signs of excessive blow-by.
8. If the wiring and ventilation are sound, test or substitute the sensor as the manufacturer procedure directs.

How to fix

• Repair or replace damaged wiring, and restore the correct signal, reference and ground circuits.
• Clean, repair or replace corroded or damaged connectors and terminals.
• Replace the crankcase pressure sensor if it fails testing.
• Repair or replace blocked or damaged crankcase ventilation components, and address any underlying cause of excess blow-by.
• Update or correct the engine control unit software only if the manufacturer lists an outdated calibration as a known cause, or repair or replace the control unit if testing proves it faulty.

Can I keep driving?

Nearby codes

• P051CGenericCrankcase Pressure Sensor A Circuit Low
• P051EGenericCrankcase Pressure Sensor A Circuit Intermittent/Erratic