engine management problem

[Malcolm27]

Hi my Vauxhall Corsa b 1.2 16valve year 2000. battery went flat i think it was probably lack of use more so now due to corona virus, my neighbour had some jump leads he attached the leads to my car battery his car had its engine running. I saw that he had connected the leads the wrong way round on my car battery! (Note my ignition was off) he reconnected them the correct way round! ,I started my engine and heard various clicking noises thinking the system was resetting its self. I could see my engine management light was flashing all the time ! my engine's fast idle didn't' seem to be working, but the normal idle speed was ok. I tried revving it but it held back then I managed to catch the throttle and rev it to about 4.000rpm but the light stayed on and it then seemed to go in to limp mode I presume the ECU has logged a fault code! Any idea what the problem fault is ? I had no problems before the battery went flat or could the jump leads connected wrongly have caused the problem? Thanks Silverfox .

[Pegscratch]

You've probably cooked something. I'd start by taking the battery leads off completely for now, giving it ten minutes, reconnecting it all back up and then seeing what happens. You may need to clear fault codes but past there on a 2000 Corsa you're probably shopping for a new car.

[Malcolm27]

Hi I charged the battery yesterday and left it connected on the car overnight. I have just been out to start it "But Battery has gone flat again! I'm wondering if its got a dodgy cell that's causing the battery not to retain the charge overnight ! Probably the battery is kaput it's been on since I got my car in 2010! Onley way is to get it checked with a heavy discharge tester ( I don't have one any more)and see if any faulty cells show up ! My local parts shop will test it! If its a new battery that's needed I will have to buy one! I will then have to have the ECU checked out for a fault code and get it reset hopefully every thing then will be ok. Oh I'm nearly 71yrs old now a worn out retired car mechanic ! Thanks for now. Silverfox.

[GreenV8S]

Reverse polarity could have damaged all sorts of things, but if it runs at all that's a good sign. I'd start by disconnecting the alternator and testing that.

[Pegscratch]

Alternator would be one of the first things I'd be wondering about the condition of. Theory is if you connect one to the other the wrong way around you create a circuit that has effectively no voltage. This will be countered by the fact that your battery was dead (probably very low 12v on a good day) versus 14.4+v on the running car you were attached to; so you will likely have had a few volts incorrect polarity. Many electronics *may* have survived but alternators aren't a big fan of it. By the time you sort alternator, battery and any costs associated unless you've a very friendly garage, you're going to be heading towards the value of the car - then you're still not through all of the electronics that might have had a strop.