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Battery Drain - fuse 40 and relay 429

Posted: Fri Oct 13, 2017 8:42 pm
by armagh02
I have long running problem with battery drain on 2007 1.2 polo. Drain is 0.3 amp (battery goes flat over a couple of days) - when draining the throttle body is running intermittently and relay 429 is warm - when fuse 40 (ECU) is pulled the drain stops and even when fuse 40 is put back in the drain doesnt start again until the car is started. I tried changing relay 429 but then the power steering pump packed in - coincidence?? - any ideas

Re: Battery Drain - fuse 40 and relay 429

Posted: Sat Oct 14, 2017 10:29 pm
by RUM4MO
There is a situation with later cars where the BCM can end up keeping some normally sent to sleep power supplies awake due tom S/W errors, these can be fixed by a BCM S/W fix/patch, but it sounds like what you have here is a faulty "part" that is keeping the system awake, this car probably does not have a BCM the CCM probably covers this activity and it sounds like there is a fault that is wakening up these normally switched off or sent to sleep switched power supllies. So they all need checking, you know that it is engine ECU activity that is draining the battery, you need to get someone to narrow that down to a function, wire or assembly to stop this happening.

Re: Battery Drain - fuse 40 and relay 429

Posted: Mon Oct 16, 2017 6:33 pm
by armagh02
Thanks I have had a diagnostic scan but there is no faults found - mechanic thought it might be faulty ignition switch? could the ECU be faulty?

Re: Battery Drain - fuse 40 and relay 429

Posted: Tue Oct 17, 2017 12:45 pm
by RUM4MO
Unfortunately this sort of problem rarely ends up showing much on a scan, what is needed is a basic understanding of which systems get put to sleep and when, with that knowledge the next thing to do is to isolate selected areas by removing fuses and checking for resulting current drain over a long period of time! Not too easy and can be very time consuming, but if you know what you are doing, you will locate the area that is being either kept awake or being wakened up due to an issue.