What it means
Same as P051A with the signal voltage below 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 sends a signal that lets the control module monitor crankcase pressure and PCV operation. P051C sets when that signal falls below the circuit’s expected range. A signal wire shorted to ground, poor connector contact, or chafed wiring can pull the reading low.
Common causes
Most likely first.
- Signal shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
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
- Capture freeze-frame data and monitor sensor A’s signal on a scan tool to confirm it is reading low when P051C is active.
- Inspect sensor A’s connector for water, corrosion, pin push-back, or a loose fit that could create high contact resistance.
- Trace the signal wire near the sensor and along its harness for chafing, crushed insulation, or contact with ground.
- Move the harness gently while watching the live signal to see whether the low reading changes with wire position.
- Test the signal circuit for a short to ground and check power and ground against the manufacturer’s specification before condemning the sensor.
Common fixes
- Clean and secure corroded or loose sensor A connector terminals.
- Repair the chafed signal wire and protect it from rubbing against nearby parts.
- Repair a signal wire short to ground or a damaged harness section.
- Replace crankcase pressure sensor A if its signal remains low despite a verified, sound circuit.
Can I keep driving?
If the engine is stable and there is no oil leaking, keep any necessary drive short and gentle while arranging diagnosis. Stop if rough running worsens or oil begins leaking, since incorrect crankcase pressure can aggravate seal leaks.
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.