Check Engine Light - Advice Please

[Wozzathelad]

So...I loaned the GTA to a mate for a few days. They happened to be the most rain soaked days in the history of rain soaked days, which could be relevant. The car was dropped off this morning and my friend was looking worryingly apologetic. On the drive down from the central coast to Sydney (60 mile drive in torrential rain), the check engine light came on, and he pulled over. Temps were fine, oil was good and he thought that switching off would reset the warning. It didn't.

The car arrived at mine with no further dramas and I started it up to park it. Sure enough, after about 10 seconds, the light came on. I'm thinking o2 sensor?. Could be a false reading caused by the amount of wet weather driving its done?. Any ideas on other possibilities and can you hook up one of those OBD scanners to look at fault codes?.

Any help appreciated.

[Dangerm]

I made the mistake of cleaning under the bonnet of my 166 with a water hose once. Gearbox had a spaz, and warning codes galore. I didn't realise the level of chipping/electronics in the motor bay of cars today as I mainly own classics. Took 4 days to dry out properly....