Motronic ECU battery drain/relay fault?

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Mamod17
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Joined: Sun Aug 30, 2015 8:41 am
Location: Sydney

Motronic ECU battery drain/relay fault?

Post by Mamod17 »

Hi,
I have a battery electrical drain coming from possibly the ECU or this part (relay?) highlighted. I've looked on wiring diagrams but can't figure it out. Car turns over and starts fine, but when this part is unplugged, the electrical drain disappears but the car won't start. Could it be a faulty ECU or relay something else? Thanks 😅

1980 635csi VIN NO: 5585576
Part looks like a relay 1373812.3 3/85
Moronic ECU: 0261200002
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1980 JPS635csi Group C Tribute
1986 635csi 5speed Alpine White M-Tech Aust Del
2001 325ci Auto Orient Blue

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1988 635csi Auto Zinnerbot
1988 320i Convertible
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Ralph in Socal
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Re: Motronic ECU battery drain/relay fault?

Post by Ralph in Socal »

That’s typical location for the main relay in series 1 cars. 5 prong and probably is. It powers multiple accessories including the ecu. I would swap that out first with a known good unit. You can also try to determine where the current is going as you may have a failed switch. Good luck

Ralph
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
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88 528e Bronzit (Granpa Car)
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Mamod17
Posts: 124
Joined: Sun Aug 30, 2015 8:41 am
Location: Sydney

Re: Motronic ECU battery drain/relay fault?

Post by Mamod17 »

Thanks Ralph, will try that 👍
1980 JPS635csi Group C Tribute
1986 635csi 5speed Alpine White M-Tech Aust Del
2001 325ci Auto Orient Blue

Previous
1988 635csi Auto Zinnerbot
1988 320i Convertible
bpoliakoff
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Re: Motronic ECU battery drain/relay fault?

Post by bpoliakoff »

My 81 Euro with Motronic, same ECU as yours,. It was idling in the driveway and quit. After checking for fuel, the coil etc We found it to be a relay,5 prong as Ralph said , and mounted in the same place as yours
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.
Mamod17
Posts: 124
Joined: Sun Aug 30, 2015 8:41 am
Location: Sydney

Re: Motronic ECU battery drain/relay fault?

Post by Mamod17 »

bpoliakoff wrote: Wed Dec 22, 2021 11:39 pm My 81 Euro with Motronic, same ECU as yours,. It was idling in the driveway and quit. After checking for fuel, the coil etc We found it to be a relay,5 prong as Ralph said , and mounted in the same place as yours
Thanks for the feedback. Exactly the same thing happened to me. Car idling then quit. Happened a couple of times. Got it going went around the block and waiting for garage door to open cut out on me again. Feels like once the car (or electrics) warmed up the issue became apparent. Then it just refused to start. Battery cabling was a mess so we changed our and remounted the grounding cables the zI could start and hasn't given me trouble since. But tracing the battery drain let us to the relay, so I suspect they may have been separate issues. :lol:
1980 JPS635csi Group C Tribute
1986 635csi 5speed Alpine White M-Tech Aust Del
2001 325ci Auto Orient Blue

Previous
1988 635csi Auto Zinnerbot
1988 320i Convertible
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