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Battery Drain - fuse 40 and relay 429

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armagh02
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Joined: Fri Oct 13, 2017 8:32 pm
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Location: northern ireland

Battery Drain - fuse 40 and relay 429

Post by armagh02 » Fri Oct 13, 2017 8:42 pm

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

RUM4MO
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Drives: B8 S4 & 6R/6C1 1.2TSI 110
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Re: Battery Drain - fuse 40 and relay 429

Post by RUM4MO » Sat Oct 14, 2017 10:29 pm

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.

armagh02
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Posts: 2
Joined: Fri Oct 13, 2017 8:32 pm
Drives: 9n
Location: northern ireland

Re: Battery Drain - fuse 40 and relay 429

Post by armagh02 » Mon Oct 16, 2017 6:33 pm

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?

RUM4MO
Bling Bling Diamond Member
Posts: 2798
Joined: Sat Dec 30, 2006 9:12 pm
Drives: B8 S4 & 6R/6C1 1.2TSI 110
Location: Mid Lothian

Re: Battery Drain - fuse 40 and relay 429

Post by RUM4MO » Tue Oct 17, 2017 12:45 pm

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.

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