Cancelling engine warning light
 

Citroen Saxo Desire, 1.1L. Engine began to run rough. Engine management light came on. Went for easiest option and checked spark plugs. One had failed (oiled up). Stuck a replacement plug in - problem solved, running well again.
Warning light remains on though. I know it has to be re-set using a diagnostic unit, but I keep reading that disconnecting the battery for an hour or so and then re-connecting it will re-set the light.
Anybody tried this - did it work?

You need to find out why the spark plug oiled up,or you'll be forever changing the plugs mate.

I replaced all the plugs around five weeks ago. No problems yet. Could it just have been a failure of the original plug itself, which would mean it wasn't sparking and therefore oiling up? The plugs had never been changed since the car was new in year 2000 apparently.
Would still appreciate advice about my original query.

Disconnecting the battery won't reset the light,you can buy cheap OBD readers on ebay to clear the fault codes.Or a garage could do it cheaply for you.

That's not how the EML works

The light will only stay on if a problem persists, when the problem goes away the light goes out but the code stays stored.

You need to know what the code is to have any idea of where to look, in order to start fixing it.

an oiled up plug would point to a mechanical issue, stem seals/rings etc.

It wasn't just wet and sooty from a misfire? definitely oil?

Will have to check plug again for any repeat of the oiling issue. If its shows signs of oiling up again I guess there may be a seal problem. Over five weeks now since I fitted a new set and still running normally.
Just a final query. Does a year 2000 Saxo 1.1 Desire have a multi-pin OBD connector under the dash? If so, where exactly is it?

Keep an eye on it, but if there is still a problem the light remains lit. It could be unrelated.

If it is an mpi engine with 3 plug ECU, this is OBD-II compliant. The socket is next to the bonnet release.

If it is a single plug ECU, this is not OBD compliant and you will need PEugeot Planet software/diagbox with lexia cable to read the fault codes. The socket is in the same place and looks identical to the OBD-II. (some generic garage computers can read these ECU's such as Snap On Modis etc) :y:

UPDATE: Used the vehicle for months without any issues, but the warning light remained lit throughout. MOT time came along and placed a discreet strip of black tape over the light.
Car Passed the MOT without incident, emissions ok. ODB Code Reader received at Christmas useful present!). Three codes detected.P0304 (Misfire all cylinders), P0711 (transmission fluid temp.), P1B00 (Undefined?).
Regarding the misfire code, the engines runs normally under acceleration, normal cruising and smooth idling. I suppose transmission fluid temp. could be faulty sensor.
I erase the fault codes and switch MIL (warning light) to OFF and car runs for a couple of days without light re-appearing. Then out of the blue, it lights up again.
I am thinking about changing the coil pack, but with the car running fine, I wonder whether this is necessary. Any one else had similar trouble?

P0304 is specific to cylinder number 4. Misfire on all cylinders is P0300. Your MOT certificate may indicate a misfire this if they supplied you with an emissions sheet because every time the car misfires, the ppm will go up by 1 - providing it's not burning any oil! These engines run really clean when in good order. Your ppm limit is 200, if it shows 100 or something, there is a misfire or burning oil etc and would still result in a pass.

The other 2 codes point to a potential ECU fault. There are no transmission temperature sensors. Could just be a spurious error. Some codes are allowed to be set by the manufacturer. In which case you need PP2000/Lexia/Diagbox to read the correct definition of the codes supplied as a generic reader (such as ELM etc) won't be giving you the correct definitions.

Anyways, going back to your misfire code, that triggers when the ECU detects a certain number of misfires over a period of time - you won't necessarily feel them.