Smudge46

iTrader: (1)

My check engine light doesn't come on at all. It's supposed to light up when you first turn the key but mine doesn't. When I first got my car (03 STI) nearly a year ago it had a full decat exhaust on so I just assumed that the person who had it prior had removed it to stop it coming on. I've looked at the rear of the instrument panel but I can't see which bulb is for the Check engine light. I'll put some pics on tomorrow of the rear of the panel.
Just a thought but can you turn the light off permenantly?

Splitpin

You can't "turn the CEL off" permanently - well you can, but the only way to do it would be by rewriting and reprogramming the ECU firmware, so while it's technically possible it's unlikely.

Far more probable to be either a bust bulb or, as you say, the previous owner has pulled it for some reason (or possibly cut a wire betwen the ECU and instrument cluster). If you can't see which bulb it's meant to be, just remove one at random and hold the instrument panel up to the light (or point a torch into the hole the bulb came from). You should be able to see the logo of whatever bulb it is you removed. Keep going until you find the CEL. If any of the bulb holders are missing, start with them first.

Boro

iTrader: (1)

I wouldnt say turning the ECU light off with a remap was unlikely. Infact id say it was more than likely. Thats if, turning it off does so permanently.

Splitpin

Why would you say it's "more than likely"?

Smudge46

iTrader: (1)

Thanks for the replys. I've tried looking to see which bulb it is but when you look at the back of the panel the bulbs don't line up with the rear of the cel sign.

I'll take some pics and show you what i mean

Boro

iTrader: (1)

IIRC, by sticking a full decat on an STI, a remap would be high on the list of things to do to prevent possible engine failure. If the car went in for a remap after having the decat fitted, it would have been easier to map the light out than remove the bulb.

This is assuming the car has been mapped for the decat of course.

Midlife......

iTrader: (2)

You can "map out" specific CEL's such as the de-cat CEL P0420 etc. but you can't actually switch the cel light off completely with a re-map.

Aftermarket ECU's can use the CEL light for other uses such as det detection (Apexi) though.

Sounds like a non-functioning or absent bulb or some black tape placed over it.

Shaun

Splitpin

No it wouldn't. Deactivating the CEL in firmware completely is possible, but to do so requires rewriting of the ECU code - and this is something that tends to be more than most mappers would normally do. Pulling the bulb would be far quicker.

In any case, deactivating the CEL completely would deprive the driver of a sometimes crucial opportunity to pick up engine issues before they become critical. Programming out certain error codes to map round a decat is one thing. Switching it of completely is a bad idea all round.