What Does P051C Mean?
The crankcase pressure sensor circuit is reporting a voltage that is below the minimum expected threshold. This typically means the sensor signal wire is reading near 0V when it should be within a normal operating range. The driver will see the check engine light and may not notice any immediate drivability symptoms, though the PCV system cannot be properly monitored by the ECM.
Common Causes
35%
Short to ground in the sensor signal wire
30%
Failed crankcase pressure sensor with internally shorted output
20%
Corroded or water-damaged sensor connector causing low resistance path to ground
10%
Open 5V reference circuit causing sensor to output minimum voltage
5%
ECM driver circuit fault pulling the signal low
Diagnostic Steps
1
With key on engine off (KOEO), measure the voltage at the crankcase pressure sensor signal pin at the sensor connector — should be approximately 0.5-4.5V. A reading near 0V confirms the low circuit condition.
2
Verify 5V reference supply is present at the sensor connector. If the reference voltage is missing, trace the 5V reference circuit back to the ECM, checking for opens. Note this reference may be shared with other sensors.
3
Disconnect the sensor and check if the signal voltage at the ECM side of the harness rises to approximately 5V (pulled high by the ECM). If it does, the sensor is internally shorted — replace it.
4
If voltage remains low with the sensor disconnected, check the signal wire for a short to ground using a multimeter (resistance to chassis ground should be >10 kOhm). Inspect the harness for chafing, especially near engine mounts and hot exhaust components.
5
Inspect the sensor connector for signs of moisture, corrosion, or green deposits on pins. Clean with electrical contact cleaner and apply dielectric grease.
Estimated Repair Cost
$60 - $300
Parts + labor, varies by vehicle and location
The crankcase pressure sensor circuit is reporting a voltage that is below the minimum expected threshold. This typically means the sensor signal wire is reading near 0V when it should be within a normal operating range. The driver will see the check engine light and may not notice any immediate dri...
The most common cause of P051C (Crankcase Pressure Sensor Circuit Low) is: Short to ground in the sensor signal wire
Typical repair costs for P051C 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 cases. The ECM will use default values for crankcase pressure monitoring. However, the PCV system is not being actively monitored, so any developing PCV issues would go undetected. Address the repair at your earliest convenience.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P051C 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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