P051D: Crankcase Pressure Sensor A Circuit High
What to do
Ask for the connector to be checked first — including simply that it is plugged in. This sensor sits on the cam cover on many engines, which comes off for spark plugs and gasket work, so one left disconnected after servicing is a common and free-to-fix cause.
Mention any recent work on the top of the engine, however unrelated it seems.
Ask for the sensor's earth connection to be tested, not just its signal wire. A lost earth makes the signal read high and is easy to miss.
Ask for the breather system to be checked at the same time. While this sensor is faulty nothing is watching for a blocked crankcase breather — which is the fault it exists to catch, and the one that pushes oil past the crankshaft seals.
What this code means
The crankcase pressure sensor's signal is above the highest voltage the circuit should produce.
High and open are indistinguishable from inside the module, because these inputs carry a pull-up the module sees whenever nothing is loading the circuit. The measurement that separates them is made at the connector with the sensor unplugged, and it takes a minute.
The trivial cause deserves eliminating first. This sensor is mounted on the cam cover on many engines, and the cam cover comes off for spark plugs, coil packs, gaskets and breather work — so a sensor left unplugged after routine servicing is a genuinely common finding and costs nothing to check.
Beyond that, the ordinary open-circuit causes apply: a corroded terminal that has lost contact, a wire broken inside intact insulation where the loom flexes, or a lost earth floating the signal high.
Check the sensor's ground rather than only its signal wire. It is easy to overlook and produces exactly this reading.
A sensor failed internally open is the honest last conclusion. It happens, but everything above it is cheaper and more likely.
Do not skip the breather check while you are there. This sensor's whole purpose is to notice a blocked or disconnected crankcase ventilation system, and a fault in its circuit means nothing is watching for that — which is the real cost of leaving it.
Likely causes
Start here
- Open circuit in sensor wiring · moderate
- Sensor left disconnected after previous work · easy
- Corroded or loose connector · easy
Less common
- Open sensor ground circuit · moderate
- Faulty crankcase pressure sensor · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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