davtur87 Posted February 17, 2021 Share Posted February 17, 2021 Hi guys, My car is a Ford Focus 1.6 petrol, 2007 I made a very stupid mistake yesterday. I fitted a new battery, and I connected the battery the wrong way around (+ to -, and - to +). There was a loud whirring noise and I quickly disconnected it and realised my stupidity. I've now connected the battery the correct way around, and now the car won't start up. The electrics seem to be still working, the central, locking, dashboard, eletric windows are all fine. However, the car won't turn over and the dash is showing 'engine system fault'. I did some reading online, and some people are saying 'it will have fried everything' and others say there are fuses to protect the components of the car including the ECU. Has anybody got an ideas about what I can try? Thanks very much in advance 1 Quote Link to comment Share on other sites More sharing options...
JW1982 Posted February 17, 2021 Share Posted February 17, 2021 Fuses are only intended to protect the electrical system from overcurrent. Reversed polarity is not protected by the fuses in any way. There is a huge chance that the reversed polarity damaged the PCM. 1 Quote Link to comment Share on other sites More sharing options...
davtur87 Posted February 17, 2021 Author Share Posted February 17, 2021 Not what I wanted to hear, but thanks for your advice! Sounds like my best option is to get it booked in to a garage for them to confirm this.. Am i right in thinking that if it is the PCM, then I'm looking at hundreds of ££s to sort it? Thanks again mate Quote Link to comment Share on other sites More sharing options...
AR7530v6 Posted February 17, 2021 Share Posted February 17, 2021 32 minutes ago, JW1982 said: There is a huge chance that the reversed polarity damaged the PCM. Well, protection against wrong polarity is cheap and simple and also kind of basic matter in electronic designing. And as said, it's not implemented by fuses, but it's internal feature of module. I doubt, that the manufacturer (Bosch, Magneti Marelli, Lucas, etc.) of car electronics would left wrong polarity or overvoltage protection away from their modules.🤔 There are so many possible faulty devices from broken wire, fuse, relay or sensor to electronic module(s) - or maybe the reverse polarity protection just operated as it's designed. Also, error codes may help for troubleshooting. I prefer to book the garage. Quote Link to comment Share on other sites More sharing options...
Jonro2009 Posted February 17, 2021 Share Posted February 17, 2021 Have you checked the high ampere fuses in the engine fuse box? It's worth checking them and seeing if there is any 'basic' reasons for the problem. As @AR7530v6 says it's unlikely but not impossible that any part of the ECU is fried. Check all the fuses in the engine bay and then move on to the fuses in the cabin, although it's less likely one of those has blown. It's worth doing the simple stuff first. Are you able to connect a fault code reader up? Quote Link to comment Share on other sites More sharing options...
davtur87 Posted February 24, 2021 Author Share Posted February 24, 2021 Thanks for the replies lads. I’ve checked the fuses and they all appear to be ok. Biting the bullet and getting an auto electrician out to have a look. Thanks for all your advice 1 Quote Link to comment Share on other sites More sharing options...
StephenFord Posted February 24, 2021 Share Posted February 24, 2021 1 hour ago, davtur87 said: Biting the bullet and getting an auto electrician out to have a look. Thanks for all your advice Don't forget to report back so we all learn! 3 Quote Link to comment Share on other sites More sharing options...
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