Crank no start, ecu fuse blowing

[Rcryan7]

Fuse 29 ecu fuse is blown, my car shut off at idle. The fuse blows every time I start it or try to start the car .
I looked under coolant res to find the coolant sensor wire ripped, and the ecu wiring harness running on the notorious bolt, which ripped through the housing, but I do not see any wires ripped .
Cranks but no start now
2001 s4 manual
Any help would be appreciated
Thanks


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[PwrWgn]

I took a quick look at the wire diagrams and I see the Fuel pump Relay feeds that S29 fuse circuit. It then goes to supply power to the ICMs....maybe just some places to look closer at.

[SideMirror]

Use a multimeter, coil wire diagram, open up EUC box cover, and begin to check each coil wire for shorts between the coil connectors and ECU, Ohms testing. Google how to check relays using a 9v battery.

This link will help you understand how the coil connectors pin outs.

https://www.audizine.com/forum/showt...rsion-Hardwire

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[Silverex]

Use a multimeter, coil wire diagram, open up EUC box cover, and begin to check each coil wire for shorts between the coil connectors and ECU, Ohms testing. Google how to check relays using a 9v battery.

This link will help you understand how the coil connectors pin outs.

https://www.audizine.com/forum/showt...rsion-Hardwire

Sent from my Pixel 7 using Audizine Forum mobile app

Do the coils even get power from fuse 29?


If he does want to check the coils, the power wire (red/green) all get tied together by Ecu then goto T10ar/1 (orange connector under Ecu).

[RMode]

Wires underneath the coolant overflow are arcing, or, coil packs are. I have some decent pics in my build thread, as I had the exact issue a couple months ago

[Rcryan7]

What’s arcing? Thanks


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[Rcryan7]

Don’t worry I looked it up thanks , so wires are touching , I don’t want to cut the harness protecting but I think I will be able to seal it back up OEM
Thanks
I could only think they would be touching somewhere or I also heard it could be a bad ecu, are you referring to the coil packs themselves ?


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[SideMirror]

Do the coils even get power from fuse 29?


If he does want to check the coils, the power wire (red/green) all get tied together by Ecu then goto T10ar/1 (orange connector under Ecu).

fuse 29 provides power from the fuel pump relay to the ignition coils and the leak detection pump.*

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[RMode]

Don’t worry I looked it up thanks , so wires are touching , I don’t want to cut the harness protecting but I think I will be able to seal it back up OEM
Thanks
I could only think they would be touching somewhere or I also heard it could be a bad ecu, are you referring to the coil packs themselves ?


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For my car, the primary culprit was the body side of the crank sensor harness - 3 pin plug right under the coolant overflow. It was brittle, which causes the copper strands of the wire to become exposed, and then once 2 of those touch, it’s an immediate short. Another somewhat common thing is again, that same area, where the engine harness goes to the ecu, there are 1 or 2 studs on the firewall. Over time and again due in part to heat, the harness rubs the stud, and causes the insulation of the wire to erode, and it will also cause shorts.

What I did was basically as described in my thread: I removed the coolant bottle, and inspected each wire in the general area one by one. I fixed every single area where there was exposed wire or where the wire insulation was very worn. But the main solution to my fuse 29 issue was the crank harness itself. For that I replaced the car side of the plug completely with a new one, 3 fresh wires spliced in, and it was done.


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