What it means
Same as P051A with the signal voltage above the plausible range. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
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 measures crankcase pressure for the control module’s assessment of the PCV system. P051D sets when the sensor signal rises above the circuit’s expected range. A signal shorted to the supply voltage, including wiring pinched against a battery feed, can make the reported pressure appear abnormally high.
Common causes
Most likely first.
- Signal shorted to supply
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
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
- Save freeze-frame data and check sensor A’s live signal to confirm that the high reading is present when the fault occurs.
- Inspect the sensor connector for corrosion, loose terminals, water ingress, and pins that have moved backward.
- Trace the signal wire for pinched or damaged insulation, especially where it passes near power wiring or sharp edges.
- Move the harness gently while monitoring the signal to check for a reading that changes with wire movement.
- Test for a short to supply voltage and verify the circuit’s power, ground, and signal against the manufacturer’s specification.
Common fixes
- Secure or repair loose, corroded, or damaged sensor A connector terminals.
- Repair the signal wire where it is pinched or chafed against a supply wire.
- Repair a confirmed short to supply voltage in the sensor harness.
- Replace crankcase pressure sensor A if the circuit checks out but its output remains high.
Can I keep driving?
A short, gentle drive may be reasonable if the engine runs normally and there are no oil leaks, but arrange diagnosis soon because the high signal prevents reliable PCV pressure monitoring. Stop if rough running becomes severe or oil starts leaking.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.