Faulty oil pressure sensor or switch B; Damaged, chafed or oil-soaked wiring to the sensor (open circuit, short to earth or short to voltage); Corroded, loose or contaminated connector at the sensor or control unit; Genuinely low or incorrect oil pressure caused by low oil level, wrong grade, diluted oil, worn pump or worn bearings; Fault in the sensor reference voltage supply or earth shared with other sensors; Faulty control unit or its internal sensor circuit.

P055A

Engine Oil Pressure Sensor/Switch B Circuit.

Generic
Powertrain
Generic code
Medium severity

How this code is built

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

What it means

P055A is the generic code for a fault in the circuit of engine oil pressure sensor or switch 'B'. The engine control unit saw a signal or voltage from that sensor circuit outside the expected range. This points to a sensor, wiring or connector problem, but it can also be a real oil pressure or oil condition issue. Which sensor is 'B' and the exact fault limits depend on the make, model and engine.

Symptoms

Engine warning light on
Oil pressure warning light on, flickering or showing falsely
Oil pressure gauge reading erratic, zero or maxed out
Engine entering a reduced-power or protection mode on some models
Other oil-related or sensor supply fault codes stored

Possible causes

Faulty oil pressure sensor or switch Blikely
Damaged, chafed or oil-soaked wiring to the sensor (open circuit, short to earth or short to voltage)likely
Corroded, loose or contaminated connector at the sensor or control unitlikely
Genuinely low or incorrect oil pressure caused by low oil level, wrong grade, diluted oil, worn pump or worn bearingspossible
Fault in the sensor reference voltage supply or earth shared with other sensorspossible
Faulty control unit or its internal sensor circuitrare

How to diagnose

Read all stored codes and freeze frame data, noting engine speed, oil temperature and when the fault set, then check for related codes
Check the oil level and condition, and confirm the correct grade has been used, before anything else
Visually inspect the sensor, its wiring and connector for oil leaks, chafing, heat damage, corrosion and bent or pushed-back pins
Check live data for the oil pressure signal at key on and at idle, and see if it is stuck, erratic or implausible
Check the wiring diagram for your model, then test the sensor supply, signal and earth at the connector for correct voltage, continuity and shorts
Verify actual oil pressure with a mechanical gauge to separate a real pressure problem from a sensor or circuit fault
Wiggle-test the harness with the engine running and watch the live signal for dropouts
Compare sensor resistance or output against the manufacturer's specification for the engine

How to fix

Top up or change the oil and filter with the correct specification if level or condition is the cause
Replace the oil pressure sensor or switch if it is faulty or leaking
Repair or replace damaged wiring and fix any open circuits or shorts
Clean, repair or replace corroded or loose connectors and terminals
Investigate and repair the engine if a mechanical gauge confirms genuinely low oil pressure
Repair the shared supply or earth fault, or as a last resort have the control unit diagnosed and replaced

Can I keep driving?

Medium severity

Short, gentle trips are usually acceptable if the oil level is correct and no oil pressure warning is showing, but get it fixed soon. If the oil pressure warning light comes on or the gauge shows low pressure, stop driving and switch off the engine, as running without oil pressure can quickly destroy it.

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