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View Full Version : Electrical puzzle for you guys!



Sgoff2006
08-19-2024, 08:50 AM
2011 s4. All stock. 110k miles. I have been having crank/no start problems (with alot of codes) alot recently. First it started out doing it only when the car sat overnight and progressively is getting worse and worse. I can make it start everytime by unhooking the battery for a second and hooking it back it up. After that it fires up perfectly.

-here are the codes while the crank/no start condition is happening https://imgur.com/a/ibL4Pvg
When I clear the codes with obdeleven they all go away except https://imgur.com/a/qsblGYV

I thought maybe battery, but mine is new and here is specs of it during the no start. .https://imgur.com/a/17byooY
https://imgur.com/a/titKulj

Also when the car is not starting, should my fuel pressure be this high? https://imgur.com/a/Qmja48Q


Remember, all I have to do to make it all go away and fire right up, is unplugging the battery.

Things I have tried
-checked all fuses in ecu fuse box and swapped the 2 634 relays with each other
-logged my battery's performance
-cleared codes swapped the relays in the trunk fuse box with each other.
-to make sure I wasn't leaking fuel pressure in the lines or injectors, I logged fuel pressure while it was running and made sure it increased slowly after turning the car off

I'm illiterate to actually checking relays with meters and reading wiring diagrams. It sucks to have to unhooking and hook back up battery 4x a day :( help me out

Sgoff2006
08-19-2024, 10:01 AM
Just found another clue... in the trunk fuse box there are 2 relays labeled "634". We'll I took them both out and hooked each of them to a 9v battery and you can hear one click but not the other. I put the good one in the left slot and bad one in the back spot in the fuse box and it started right up. Does anyone know what these fuses do and if they are exchangeable with other relays that can be found locally?


EDIT:
Nevermind, it's already crank/no start again -.- my life.
I'm defiantly on to something about that relay though I think, I just checked the 3 "643" relays in the underwood ecu fuse box with a 9v battery and they all checked out. So i hope it maybe just this 1 relay that needs replaced