Engine management warning light on then off

Last night I drove my car to the MOT station to leave it there. overnight. All was perfectly normal. This morning I received a phone call to say that my C3 Picasso Exclusive 1.3 BlueHDi had failed because they engine management light remained on (in fact I think they were suggesting that nearly all the lights were on at first). They said it had been driven a short distance to see if it would clear but that it had remained on. When I asked if they'd plugged in a code reader they said it would cost £48.50!
As it was being serviced at the same time I asked them to go ahead with that anyway. A short while later I received a phone call to say that when they went to move the car onto the ramp for servicing, the light had gone off and that they were now able to pass it for the MOT.
Has anybody else ever had this happen? If it had been a dodgy garage I would have said it sounded like a scam, but it is a local one with a very good reputation.
Also, now knowing the cost of a simple diagnostic check, can anybody recommend a reasonably priced, non-professional code reader? Nothing too fancy, but good enough to pinpoint any problems. I think I should be able to buy one cheaper than the cost of getting a reading.

Hi

Yes, the check engine light will at time go out by itself just as mysteriously as it came on.

The engine ECU will check for fault status and if after a pre-determined number of engine starts or runs or wheel revolutions without fault, the light will clear. It all depends on what the fault was and you need to read them to find out.

This Autel OBD2 reader on amazon will read the basic codes.

You should have at least one stored code for the MIL the garage saw, unless they actually deleted it without telling you.


If you want anything more than OBD2, you will need a late version of lexia/diagbox