P051B: Crankcase Pressure Sensor Circuit Range or Performance

What it means

Same as P051A with the signal in plausible range yet not matching the engine model.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

Crankcase pressure sensor A reports pressure in the crankcase so the control module can assess the PCV system. With P051B, the sensor signal is electrically plausible but does not agree with the pressure the module expects for the engine’s operating conditions. A restricted sensor passage or a drifting sensor can produce this mismatch.

Common causes

Most likely first.

1. Faulty or drifting crankcase pressure sensor
2. Blocked or restricted sensor passage
3. Loose, corroded, or damaged connector
4. Open or shorted sensor wiring

Symptoms

• Check-engine light on
• Rough or unstable idle
• Whistling or hissing from the engine area
• Possible oil leaks or increased oil consumption

How to diagnose it

1. Record freeze-frame data and compare the scan tool’s crankcase pressure reading with engine speed and load to identify when it becomes implausible.
2. Inspect the sensor A connector and wiring for corrosion, looseness, or damage that could distort the signal.
3. Check the sensor passage for oil deposits or blockage that could prevent it from sensing crankcase pressure accurately.
4. Inspect PCV hoses and passages for restrictions or disconnections that could cause pressure outside the expected pattern.
5. Compare sensor A’s response with the manufacturer’s specification and replace the sensor only if the passage and circuit are sound.

Common fixes

• Clear an obstruction from the crankcase pressure sensor passage.
• Repair or replace a restricted, damaged, or disconnected PCV hose.
• Clean or repair a corroded or loose sensor A connector.
• Replace crankcase pressure sensor A if its reading remains out of range for operating conditions.

Can I keep driving?

A brief drive may be possible if the engine is running normally and there are no oil leaks, but avoid hard acceleration and have the pressure mismatch checked soon. Continued incorrect crankcase pressure can contribute to rough running or oil leaks.