P051B

What it means

P051B is the generic code for a range or performance fault in the crankcase pressure sensor 'A' circuit. The engine control unit compared the crankcase pressure signal with what it expected for the current operating conditions, or with other sensor readings such as manifold pressure and barometric pressure, and found it implausible. The signal may be stuck, drifting or out of step with the engine's actual state. The exact sensor location and how it is checked vary by model and engine.

Symptoms

• Engine warning light on
• Oil leaks or seeping gaskets and seals
• Rough or unstable idle
• Oil mist or smoke from the breather or exhaust
• Whistling or hissing from the crankcase area
• Oil consumption higher than normal

Possible causes

• Blocked, restricted or faulty crankcase ventilation system (separator, hoses, valve or breather passages), causing real pressure to be abnormallikely
• Damaged, chafed or corroded wiring or connector at the crankcase pressure sensor, including a poor ground or reference voltage faultlikely
• Faulty or contaminated crankcase pressure sensor reading out of range or driftinglikely
• Air leak in the ventilation hoses or a loose, split or disconnected breather pipe giving a false pressure readingpossible
• Excessive blow-by from worn piston rings, cylinders or turbocharger seals raising crankcase pressurepossible
• Oil level too high or oil contamination affecting the ventilation system and sensorpossible
• Fault within the engine control unit or an outdated calibration where the manufacturer has issued a known updaterare

How to diagnose

1. Read the stored and pending codes with freeze frame data and note engine speed, load and temperature when the fault set. Check for related codes such as pressure sensor or ventilation faults.
2. Check the engine oil level and condition. Look for overfilling, fuel dilution or sludge.
3. Visually inspect the sensor, its connector and wiring for damage, oil contamination, corrosion, water ingress or chafing.
4. Inspect all crankcase ventilation hoses, the oil separator and breather connections for blockages, cracks, splits, disconnection or collapsed pipes.
5. With a scan tool, view live crankcase pressure at idle and under load, and compare it with manifold and barometric pressure with the engine off and at idle. Check whether it responds sensibly.
6. Check the sensor supply voltage, ground and signal wire for continuity, shorts and voltage drop, following the manufacturer's wiring data for that model.
7. Assess blow-by with a suitable test, such as a crankcase pressure or compression and leak-down check, if the ventilation system and sensor check out.
8. Check for technical service bulletins or calibration updates for the specific model and engine.

How to fix

• Clean or replace blocked ventilation components such as the oil separator, valve and hoses as the testing shows.
• Repair or replace damaged wiring, terminals or connectors, and clean up any oil contamination at the connector.
• Replace the crankcase pressure sensor if it is confirmed faulty, then clear the code and verify the reading.
• Refit, seal or replace leaking or disconnected breather pipes.
• Correct the oil level and change the oil and filter if it is contaminated.
• Repair the underlying engine wear or turbocharger fault if excessive blow-by is confirmed, or apply a manufacturer calibration update if one is known to cover this fault.

Can I keep driving?

Nearby codes

• P051AGenericCrankcase Pressure Sensor A Circuit
• P051CGenericCrankcase Pressure Sensor A Circuit Low