P051B: Crankcase pressure sensor signal out of range
Crankcase pressure sensor circuit range/performance
Severity: Inspect soon
OBD Advisor says continued driving risks engine damage, and crankcase pressure problems can cause power loss, so get it checked soon.
It gets more serious if:
- Stop: Stop driving if the engine runs rough, loses power or a smoke or oil leak appears.
P051B in short
P051B means the crankcase pressure sensor signal is outside the range the computer expects. Overfilled oil, a dirty PCV valve, blocked PCV hoses, a faulty sensor or wiring are the usual causes. Get it checked soon, since poor crankcase pressure control can cause power loss and damage.
The engine's crankcase vents combustion gases through the PCV system. A pressure sensor tells the computer how much pressure is building.
If the signal is outside the range the computer expects for the conditions, it sets P051B.
OBD Advisor lists overfilled oil, a faulty sensor, a dirty PCV valve, water in the sensor, wiring faults, damaged PCV hoses or gaskets and a failed oil cap as causes.
Most likely causes
These are general causes for this code across vehicles. None is specific to one make or model.
Cause 1: Overfilled oil or a dirty or blocked PCV system
Common general cause- Why it ranks here
- OBD Advisor lists oil overfill and PCV valve, hose and cap faults first and starts diagnosis by checking oil level and the PCV system.
- What would change this
- Rises if the dipstick reads over full, hoses are cracked or the PCV valve is clogged. Falls if those test good.
Cause 2: Faulty crankcase pressure sensor, water in it, or damaged wiring
Common general cause- Why it ranks here
- OBD Advisor lists a faulty sensor, water intrusion and wiring or connector problems.
- What would change this
- Rises if the sensor reads out of range with the engine off or the connector is corroded. Falls if a known-good check passes.
Cause 3: Engine computer software
Possible — needs testing- Why it ranks here
- OBD Advisor lists ECM or PCM software issues.
- What would change this
- Rises if a dealer shows a software update for the code. Falls if physical faults are found.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: With the engine off and level, check the oil level and look over visible PCV hoses and the oil cap.
IfOil is overfull, or a hose or the cap is damaged
It meansCorrect it and recheck.
IfOil and hoses look fine
It meansHave the sensor and wiring tested.
Step 2: Have the sensor signal, connector and wiring tested and compared with specification.
Warning:Testing live sensor circuits can damage the computer. Let a shop do it.
IfThe sensor or its wiring is out of specification
It meansRepair or replace it.
Points to: Faulty crankcase pressure sensor, water in it, or damaged wiring
IfSensor and wiring are fine
It meansAsk a dealer about software.
Symptoms
- Check engine light on
- Reduced power
- Rough idle or misfire
- Poor fuel economy
Compare with: Check engine light with loss of power
How to fix
Step 1: With the engine off, level and cool, check that the oil level is not above the full mark.
Parts and cost context
- Crankcase ventilation (PCV) valve:A PCV valve or hose is often inexpensive, but find the cause first. Labour varies; get a quote.
Labor varies by vehicle and shop; get a quote before you approve a repair.
Compare used part prices on PartPriceGuideOn your vehicle
We don't have reviewed vehicle-specific evidence for P051B yet. The causes and tests above apply across vehicles.
Related codes
No curated relationships for P051B yet.
P051B questions
Can overfilled oil set P051B?
Yes. OBD Advisor lists overfilled oil among the causes, so checking the oil level is the cheapest first step.
Sources and review
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
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