Drivable — worth looking into
Check engine came on after a wash or heavy rain
You washed the car or drove through a downpour — and the light came on. It often clears itself in a day or two.
There is no danger, but the symptom will not go away by itself: it is the early stage of something that gets pricier.
What to look at in the live data
- The freeze frame: a fault recorded right after a wash almost always points to moisture, not to a part.
- Misfires by cylinder: water in the plug wells causes them selectively, not on all cylinders at once.
- Repeatability: a code that returns in dry weather has nothing to do with water — look for the real cause.
Common causes, cheapest first
- Water in the plug wells or on the coils: the spark goes astray and misfires appear.
- Moisture in a sensor connector — the contact drifts until it dries out.
- Pressure washing forced water where it should not be: connectors low in the engine bay suffer most often.
Codes that show up with this
P0300Random/multiple cylinder misfire detectedP0301Cylinder 1 misfire detectedP0302Cylinder 2 misfire detectedP0303Cylinder 3 misfire detected
These parameters in the reference
Engine RPMShort term fuel trim B1Control module voltageO2 sensor B1S2 voltageDistance with MIL onTime run with MIL onDistance since codes clearedTime since codes clearedWarm-ups since codes cleared
Lamps that may be on
Do it step by step
Two counters and one swap answer the question a garage charges money for.How to find which cylinder is misfiring
A symptom is not a diagnosis. The same sign comes from a dozen different causes — the readings are what tell them apart, not the feeling.
How the app helps
CarScan shows exactly these readings live, remembers the highest and the lowest value of the trip, and puts them into a report you can hand to a mechanic.