Oil in engine wiring connectors VAUXHALL Corsa Mk III (D) Hatchback (S07)

You are experiencing recurring engine roughness, repeated O2 sensor failures, and oil contamination in the wiring harness connectors of your 2007 Corsa D 1.0L. Despite replacing multiple components (O2 sensor, ignition coil pack, air flow sensor, spark plugs), the problem persists, and oil is now leaking from the oil pressure switch.

Key Issues Identified

- Oil in Wiring Harness Connectors:
Oil contamination in connectors for the O2 sensor, ignition coil pack, and airflow sensor is a significant clue. This suggests oil is traveling through the wiring harness, not just leaking externally.

- Repeated O2 Sensor Failure:
Cheap replacement sensors failed quickly, and even a quality Denso sensor did not resolve the rough running issue.

- Oil Pressure Switch Leak:
The oil pressure switch is leaking oil from its seal, and this coincides with the appearance of oil in wiring connectors.

Likely Root Cause

Leaking Oil Pressure Switch Allowing Oil into Wiring Harness

This is a common issue on Vauxhall/Opel Corsas of this era. When the oil pressure switch fails, oil can leak not only externally but also internally through the electrical connector. This allows pressurized engine oil to wick along the wiring harness, contaminating connectors for sensors such as the O2 sensor, ignition coil pack, and airflow sensor. This contamination can cause short circuits, sensor malfunctions, and erratic engine behavior.

Engine wiring loom is contaminated with oil and can trigger more fault codes than you could write down. Best case scenario - Replace switch &..."

Why This Causes Your Symptoms

- Electrical Malfunctions: Oil is a poor conductor but can carry contaminants, causing intermittent shorts or resistance in sensor circuits, leading to rough running and error codes.
- Sensor Failures: Oil in connectors can damage sensitive electronics in O2 sensors and other components.
- Recurring Faults: Even after replacing sensors and parts, if the oil leak persists, new parts quickly become contaminated and fail.

What To Do Next

1. Replace the Oil Pressure Switch Immediately
The oil pressure switch is a known weak point and is inexpensive and easy to replace. Make sure to clean the area thoroughly and use a new sealing washer if required.

2. Clean or Replace Affected Wiring and Connectors
- Disconnect and inspect all connectors contaminated with oil.
- Clean the connectors with electrical contact cleaner.
- In severe cases, sections of the wiring harness may need to be replaced if oil contamination is extensive and cannot be cleaned out.

3. Inspect for Other Oil Leaks
While the oil pressure switch is the most likely culprit, check for any other leaks around the engine (e.g., rocker cover gasket, sump).

4. Clear Fault Codes and Test
After cleaning and repairs, clear the ECU fault codes and monitor engine performance. If rough running persists, further diagnosis may be needed, but resolving the oil ingress is the critical first step.

Summary Table

Issue | Likely Cause | Solution

Oil in wiring connectors | Leaking oil pressure switch | Replace switch, clean harness
Repeated sensor failures | Oil contamination of connectors | Clean/replace sensors & harness
Engine running rough | Electrical faults from oil ingress | Fix leak, clean/replace affected

Final Advice

Do not fit any more new sensors until the oil leak from the oil pressure switch is fixed and the wiring is thoroughly cleaned. Otherwise, you risk damaging new parts again. This is a well-documented problem on your model and fixing the oil leak at the source is essential for a lasting repair