A fault code doesn’t yet mean the unit or sensor itself is faulty: often it’s the plug and connector leading to it.
Possible causes
- Air leak
- Low fuel pressure or poor-quality petrol
- Spark plugs or coils (several worn at once)
- MAF sensor
- Valve timing is off
What you can do yourself
- If Check Engine is flashing, don’t load the engine: unburned petrol damages the catalytic converter.
- Think back to where you last filled up.
- Check the spark plugs and coils, look at the fuel trims on the “Sensors” tab.
Stop and don’t drive on if:
- The Check Engine light is flashing
- The temperature gauge is in the red or the overheating light is on
- The red oil pressure light is on
- Smoke from under the bonnet, a burning or petrol smell
- Strong jerking, knocking from the engine, or the car barely moves
OOleg’s tip: don’t pressure-wash the engine
Never wash the engine with a Kärcher (a pressure washer), steam or anything like that — there’s a special foam cleaner for that. Once the rubber seals in the connectors have dried out, moisture gets inside and the sensor connectors and the computer (ECU) connector rot.
OCases from Oleg’s practice
- Omoda 2023 Misfiring, vibration, Check Engine: P030400 and P030000. We moved the coil from cylinder 3 to cylinder 4 — the code stayed on cylinder 4. The culprit was the cylinder 4 spark plug, even though the set had been replaced a few thousand km earlier. How it went ↗
- Volkswagen Passat 2002 Unstable idle, misfires, about fifteen codes stored. After cleaning and adapting the throttle body the idle became steadier; next we recommended the spark plugs, HT leads, O2 sensors, EVAP, MAF sensor and a search for air leaks. How it went ↗
On Oleg’s website:Engine compression test ↗
The explanation comes from the error code reference in the AvtoElektrik PRO app.