My partner's 2009 C4 THP refused to start the other day - we'd left it in 'auto' when we'd parked it up and it didn't pick up switching it to N before trying to start. Strangely, tried again later and it was fine and the error has not recurred (so far).
Plugged in Diagbox and it came up with fault code P0991 - intermittent fault with the transmission fluid pressure sensor
I've scoured the web and can find nothing on this error code - I can't even find where the sensor is let alone where it plugs into - so I assume this must be a pretty rare issue
As it was an 'intermittent' and hasn't recurred my money is on a bad connection to the wiring loom (the car doesn't see an awful lot of use and lives outside so it's potentially prone to water in connectors under the bonnet, in fact I had to clean the coil pack connectors the other day as cylinder 2 had dropped out) but obviously I'd like to check the wiring out to potentially nip a more serious problem in the bud, like the car dying on a 'smart' (ha ha) Motorway with no hard shoulder and the resultant high probability of being dismembered by a 38-tonner!
Does anyone on the forum happen to know :-
- Where this damn' sensor lives and where the connector to the main wiring loom is?
What the car's LOS strategy is if it fails (I guess it will either go into neutral and power down or you'll be stuck in whatever gear it's in at the time)
If the sensor DOES die, what the replacement process is? At a guess as it's the EGS fluid pressure sensor it'd be the full depressurise / repressurise rigmarole via diagbox
Thinking outside of the box is better than sitting in a dark one.