Signal wire shorted to ground or chafed against the body or engine; Faulty crankcase pressure sensor with an internal fault; Corroded, damaged or loose sensor connector or terminals; Open circuit or fault in the sensor's reference voltage supply; Damaged crankcase ventilation hose or component causing a genuine pressure problem that affects the sensor reading; Fault in the engine control unit's sensor input or supply.

P051C

Crankcase Pressure Sensor A Circuit Low.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
5: AreaVehicle speed, idle control and auxiliary inputs
1C: FaultThe specific fault in that area

What it means

P051C means the engine control unit saw the signal voltage from crankcase pressure sensor 'A' fall below the expected range. This is an electrical circuit fault, not necessarily a real pressure problem. The sensor is used to monitor crankcase pressure and the integrity of the ventilation system. Its location and exact function depend on the model and engine.

Symptoms

Engine management light on
Possible rough idle or slightly uneven running on some engines
Oil leaks, whistling or oil seepage if there is also a real crankcase pressure problem
Other stored codes relating to the sensor supply voltage or ventilation system
Often no noticeable change in driving at all

Possible causes

Signal wire shorted to ground or chafed against the body or enginelikely
Faulty crankcase pressure sensor with an internal faultlikely
Corroded, damaged or loose sensor connector or terminalslikely
Open circuit or fault in the sensor's reference voltage supplypossible
Damaged crankcase ventilation hose or component causing a genuine pressure problem that affects the sensor readingpossible
Fault in the engine control unit's sensor input or supplyrare

How to diagnose

Read all stored codes and freeze frame data, noting when the fault set and whether other sensor supply codes are present
Visually inspect the sensor, its connector and the wiring harness for chafing, heat damage, oil contamination, corrosion and pushed-out terminals
Inspect the crankcase ventilation hoses, connections and oil separator for splits, disconnections or blockages, as the model dictates
With the ignition on, check the live sensor voltage reading and compare it with the manufacturer's specification
Check the sensor's supply voltage and earth at the connector, using the wiring diagram for that model
Wiggle-test the harness with the engine running and watch for the reading or code changing
With the harness disconnected, test the signal wire for a short to ground and for continuity back to the control unit
Only after the wiring and sensor are proven good, check the control unit's inputs and look for any manufacturer service information

How to fix

Repair or replace the damaged wiring section, using proper soldered or sealed joints
Clean or replace the corroded or damaged connector and terminals
Replace the crankcase pressure sensor if it is proven faulty
Repair or replace any damaged ventilation hoses or components found during the checks
Rectify any shared reference voltage fault found on other sensors
Repair or replace the control unit only once all other causes are ruled out, following the manufacturer's procedure

Can I keep driving?

Low severity

The car can usually be driven in the short term, but get it checked soon, as the ventilation system is not being properly monitored. Stop and seek help if you notice oil leaks, heavy smoke, rough running or a flashing warning light.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.