No, don't ignore it. The light going off doesn't mean the fault has cleared — it means the ECU has decided the fault isn't currently present, but the fault code is still stored. A diagnostic scan will read it. Most common causes: a misfire, a dodgy MAF sensor, or an early O2 sensor fault.
This is the question I probably get asked the most. Driver sees the orange light pop on, panics, then it goes off the next day and they think they're in the clear. They're not — and here's why.
What the light actually does
The engine management light (EML) comes on when the ECU sees a reading outside its expected range. Some faults are 'pending' — the ECU wants to see it happen a couple more times before it commits to lighting the lamp permanently. So the light can go out, but the code stays stored in memory for the next 40-odd warm-up cycles.
Common intermittent triggers
On petrol cars: a misfire under load (coil pack or plug going off), a sticky EGR valve, or an O2 sensor that's lazy when cold. On diesels: a sensor in the DPF or exhaust circuit, or a slightly stuck swirl flap. On any modern car: a loose petrol cap can throw an evap code that clears itself.
Why you shouldn't just ignore it
Two reasons. One: a stored fault code is an MOT advisory and could become a failure if the light comes back on at MOT time. Two: small faults get bigger. A misfire that's clearing itself today is killing your catalytic converter quietly — and a cat is a £400+ part.
What to do
Get a proper diagnostic scan — not the cheapo Halfords reader, a workshop scan tool that reads pending codes and live data. At Bob's it's £45 and we'll tell you exactly what's stored, what's live, and whether it needs fixing now or watching.
Will the fault code clear itself? — The light might go out, but the code stays in memory for around 40 drive cycles (a week or two of normal driving) before the ECU wipes it. So even if the light's off today, a scan tomorrow will still show what happened.
Can I just disconnect the battery to clear it? — You can, but you've solved nothing — the fault will come back next time you drive. And on a lot of modern cars, disconnecting the battery loses your radio code, window memory and steering angle reset. Get it scanned properly.
Is it safe to drive with an intermittent EML? — Usually yes for short trips. If the light is steady amber, drive carefully and book it in. If it's flashing, stop — that's an active misfire and you'll wreck the catalytic converter within minutes.