P055E
Oxygen Sensor Control Module System Voltage.
- 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
- 5E
- FaultThe specific fault in that area
What it means
P055E is the generic code for a system voltage fault reported by the oxygen sensor control module. The module monitors its own supply voltage and has seen it outside the expected range, either too low, too high or unstable. Because the module can no longer be sure its sensor readings are accurate, the engine control unit may stop using the oxygen sensor data for fuel control. Whether this is a separate module or part of the engine control unit depends on the vehicle.
Symptoms
- Engine warning light on
- Poor fuel economy
- Rough running or unstable idle
- Hesitation or poor performance under load
- Other charging or battery-related warnings, or other stored voltage codes
- Failed emissions test
Possible causes
- Weak or poorly charged battery, or a charging system fault giving low or unstable supply voltagelikely
- Corroded, loose or damaged battery terminals, earth straps or earth pointslikely
- Damaged wiring, poor connections or water ingress at the oxygen sensor control module power and earth feedslikely
- Blown fuse or faulty relay in the module's power supplypossible
- Alternator regulator fault causing overvoltage or voltage spikespossible
- Internal fault in the oxygen sensor control modulerare
- Outdated or faulty control unit software where the manufacturer has issued a known correctionrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting battery voltage, engine speed and load when the code set. Look for other voltage or communication codes.
- Check the battery's state of charge and condition with a proper battery test, and inspect the terminals for corrosion or looseness.
- Measure the charging voltage at the battery with the engine running at idle and at raised revs, and check that it is stable and within the manufacturer's specification.
- Visually inspect the wiring and connectors at the oxygen sensor control module for chafing, heat damage, corrosion, water ingress or pushed-back pins. Where fitted, check the module's location for moisture.
- Check the fuses and relays that supply the module, using the vehicle wiring diagram for the correct circuits.
- Measure the voltage and earth integrity at the module's power and earth pins with the circuit loaded, using voltage drop tests rather than just a continuity check.
- Check for manufacturer software updates or technical bulletins for this model and engine.
- If supply, earths and wiring all test good, check the module against the manufacturer's test procedure before deciding it has failed.
How to fix
- Recharge, or replace the battery if it fails a load test.
- Repair or replace the alternator or its regulator if the charging voltage is out of range or unstable.
- Clean and tighten battery terminals, earth straps and earth points, replacing any that are corroded or damaged.
- Repair damaged wiring or connector terminals at the module, and fix any source of water ingress.
- Replace any faulty fuse or relay in the supply circuit, after finding why it failed.
- Replace the oxygen sensor control module, or update its software where a manufacturer correction applies, only once the supply and wiring are proven good.
Can I keep driving?
The car can usually be driven for a short time, but book it in soon. Fuel control and emissions may be affected, and the underlying voltage problem could leave you with a flat battery or a breakdown.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.