Code
P051D
Generic
P — Powertrain
Crankcase Pressure Sensor A Circuit High
Views:
UK: 19
EN: 25
RU: 20
AI status
Completed
Completed
100%
Causes
- Shorted sensor signal wire to battery voltage (VB+) or accessory power
- Failed/crankcase pressure (PCV) sensor (internal electronics fault)
- Corroded, damaged or loose connector/pins at sensor or PCM
- Open or high-resistance ground or reference circuit
- PCM internal fault (rare)
- Contaminated or oil-fouled sensor causing electrical fault
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
- Possible rough idle, reduced driveability or hesitation (if PCM enters failsafe)
- Increased crankcase pressure or oil leaks if PCV system impaired
- Oil smell or oily residue at sensor/connector area
- Stored fault code related to pressure sensor circuit
What to check
- Read freeze frame and freeze data, confirm P051D is current or pending
- Visually inspect sensor, connector and wiring for damage, oil, corrosion or loosened pins
- Check for presence of oil/vapor contamination at sensor and connector
- Verify vehicle battery voltage is stable and within spec
- Backprobe sensor connector and measure signal voltage with key ON, engine OFF and with engine running
- Check reference voltage (typically ~5 V) and sensor ground at the connector
Signal parameters
- Sensor type: typically analog voltage output proportional to crankcase pressure (varies by vehicle)
- Reference voltage: ~5.0 V (check vehicle-specific spec)
- Signal voltage expected range: roughly 0.5–4.5 V depending on pressure (consult OEM specifications)
- At key ON, engine OFF: signal typically near a mid-range value (~1–3 V) — check vehicle spec
- High-circuit fault trigger: signal voltage above allowed high threshold (near battery/5 V)
Diagnostic algorithm
- Confirm the code and gather freeze frame data; note conditions (engine temp, RPM, load).
- Perform a visual inspection of the sensor, connector and wiring for damage, corrosion, or oil contamination. Repair visible issues.
- With key ON (engine OFF), backprobe the sensor connector: verify reference voltage (~5 V) present and a good ground. If reference missing, trace supply/fuse.
- Measure sensor signal voltage with key ON and with engine running. If signal is near battery voltage or > allowed threshold, suspect short to power or sensor fault.
- Disconnect the sensor and measure the signal wire at the harness side for voltage. If voltage is still high with sensor unplugged, trace wiring for short to power toward PCM or a splice.
- Check continuity and resistance between sensor ground/reference/signal pins and the PCM pins. Repair any open/high resistance circuits.
- If wiring checks clear, bench-test or replace the crankcase pressure sensor and retest. Use OBD data to confirm normal signal behavior after replacement.
- If new sensor and wiring are good but code returns, consider PCM input circuit fault—verify with OEM diagnostic flow before replacing PCM.
- Clear codes, perform a drive/functional test and re-scan to confirm repair.
Likely causes
- Short to battery voltage on the sensor signal wire
- Faulty crankcase pressure sensor
- Corroded connector or bent terminal causing intermittent high voltage
- Blown sensor reference fuse or wiring fault on the 5V reference
- Oil contamination inside sensor affecting the circuit
Fault status
Status
P051D - Crankcase Pressure Sensor A Circuit High: PCM detected the crankcase pressure sensor signal voltage above the expected range (possible short to battery, sensor or wiring fault).
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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