Faulty engine oil pressure sensor or switch B, including internal failure or contamination; Damaged or corroded wiring harness or connector at the sensor B circuit; Open or shorted circuit in the signal or ground wire between the sensor and the PCM; Low engine oil level or degraded oil causing incorrect pressure readings; PCM software issue or internal fault in the pressure sensor input circuit; Aftermarket oil filter or incorrect oil viscosity causing pressure deviations that trigger the code

DTC codes / P05xx · Vehicle speed, idle control and auxiliary inputs / P055A

P055AEngine Oil Pressure Sensor/Switch B Circuit

Q: What does code P055A mean?

Engine Oil Pressure Sensor/Switch B Circuit. P055A indicates that the powertrain control module has detected an electrical fault in the circuit for engine oil pressure sensor or switch B, which is a secondary oil pressure monitoring device on many modern engines. The computer compares the signal voltage from this sensor against expected values and sets the code when the circuit is out of range, open, shorted, or erratic.

P055A indicates that the powertrain control module has detected an electrical fault in the circuit for engine oil pressure sensor or switch B, which is a secondary oil pressure monitoring device on many modern engines. The computer compares the signal voltage from this sensor against expected values and sets the code when the circuit is out of range, open, shorted, or erratic.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

Illumination of the check engine light or oil pressure warning light on the dashboard
Often no symptoms besides the warning light, especially if the primary oil pressure sensor is still functioning
Intermittent or flickering oil pressure warning under certain driving conditions
Reduced engine performance or limp mode if the PCM derates power to protect the engine
Erratic or inaccurate oil pressure gauge readings if the vehicle is equipped with a real gauge

Common causes, most likely first

Faulty engine oil pressure sensor or switch B, including internal failure or contamination
Damaged or corroded wiring harness or connector at the sensor B circuit
Open or shorted circuit in the signal or ground wire between the sensor and the PCM
Low engine oil level or degraded oil causing incorrect pressure readings
PCM software issue or internal fault in the pressure sensor input circuit
Aftermarket oil filter or incorrect oil viscosity causing pressure deviations that trigger the code

How to diagnose and fix it

Check engine oil level and condition, and top off or change oil if necessary
Inspect the sensor B connector and wiring for corrosion, chafing, or loose pins
Use a scan tool to view live oil pressure sensor B data and compare with a mechanical gauge
Perform a voltage drop test on the sensor B signal and ground circuits to identify resistance
Replace the engine oil pressure sensor or switch B if electrical tests confirm it is faulty
Clear the code and verify the repair by running the engine and monitoring live data for the sensor B circuit

Don't overlook the oil condition first

A dirty or clogged oil filter can cause pressure fluctuations that mimic a sensor B failure, so always verify oil maintenance history before replacing parts.
The sensor B circuit often shares a ground with other engine sensors, so a bad ground can set P055A along with other unrelated codes.
On some vehicles, sensor B is a switch rather than an analog sensor, and the PCM only expects a simple on/off signal, so a stuck switch can set the code without any drivability symptoms.
A faulty oil pressure relief valve in the oil pump can cause actual low oil pressure that triggers the code, so mechanical pressure testing is essential before condemning the sensor.
Intermittent wiring faults that only appear when the engine is hot or vibrating are common, so wiggle-test the harness while watching live data to catch them.

Can I keep driving with P055A?

If the oil pressure warning light is not illuminated and the engine sounds normal, you can drive cautiously to a repair shop, but avoid heavy loads and high speeds. If the warning light is on or the engine is making ticking or knocking noises, stop driving immediately and have the vehicle towed to prevent catastrophic engine damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.