What Does P051D Mean?
The crankcase pressure sensor circuit is reporting a voltage above the maximum expected threshold. This typically indicates the signal wire is reading near or at the 5V reference level. The driver will see the check engine light; drivability is usually unaffected but the PCV system is no longer monitored by the ECM.
Common Causes
30%
Short to voltage (5V reference or battery) in the sensor signal wire
30%
Failed crankcase pressure sensor with internally open or high output
20%
Open ground circuit at the sensor preventing proper signal return
10%
Sensor connector damage with signal pin touching reference voltage pin
10%
ECM internal pull-up resistor or driver circuit fault
Diagnostic Steps
1
With KOEO, measure the voltage at the crankcase pressure sensor signal pin — readings near 5V confirm the high circuit condition.
2
Check the sensor ground circuit: measure resistance from the sensor ground pin to a known-good engine ground. Should be <0.5 Ohm. An open ground will cause the signal to float high.
3
Disconnect the sensor and check the signal voltage at the ECM side of the harness connector. If it drops to a normal mid-range voltage, the sensor is faulty — replace it.
4
If voltage stays high with the sensor disconnected, inspect the wiring harness for signal-to-reference shorts. Check for pinched wires, melted insulation near exhaust, or connector pins pushed back in the housing.
5
With the sensor disconnected, use a multimeter to check for continuity between the signal wire and the 5V reference wire — any continuity indicates a short in the harness.
Estimated Repair Cost
$60 - $300
Parts + labor, varies by vehicle and location
The crankcase pressure sensor circuit is reporting a voltage above the maximum expected threshold. This typically indicates the signal wire is reading near or at the 5V reference level. The driver will see the check engine light; drivability is usually unaffected but the PCV system is no longer moni...
The most common cause of P051D (Crankcase Pressure Sensor Circuit High) is: Short to voltage (5V reference or battery) in the sensor signal wire
Typical repair costs for P051D range from $60 to $300, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive in most situations. The ECM defaults to standard PCV operation without active pressure monitoring. Repair should be completed before the next emissions inspection and to restore full system monitoring capability.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P051D to identify the root cause.
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Quick Info
Category
Powertrain
System
Emissions / PCV System
Difficulty
Type
Generic (SAE)
Recommended Tools
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