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Title: ECU Doesn't Seem to Wake Up Without Excessive Battery Voltage Levels Post by: royce5950 on May 21, 2023, 01:02:54 AM What would be causing my ECU (MED9.1) to only wake up if it gets like 13 volts? I have a yellow top optima that is proper size for my Audi A4 B7 and even with the battery being at like 12.4v with the key in the on position the CEL will not come on indicating that the ECU is awake and the vehicle can be started.. But sometimes if I sit there for a few minutes randomly the CEL will illuminate and then I can start the car... But the only guaranteed way to get the ECU to wake up and get the CEL to illuminate so I can start the vehicle is hooking up the charger and getting the system up to like 12.8v or more.. Its left me stuck too many times now and even with having a ton of experience working on these cars I don't know where to begin.. My only guess is some sort of ECM power relay being worn out or something but I dont know.. Anyone care to throw a hypothesis out there?
Thank you Title: Re: ECU Doesn't Seem to Wake Up Without Excessive Battery Voltage Levels Post by: _nameless on May 21, 2023, 01:27:18 AM What would be causing my ECU (MED9.1) to only wake up if it gets like 13 volts? I have a yellow top optima that is proper size for my Audi A4 B7 and even with the battery being at like 12.4v with the key in the on position the CEL will not come on indicating that the ECU is awake and the vehicle can be started.. But sometimes if I sit there for a few minutes randomly the CEL will illuminate and then I can start the car... But the only guaranteed way to get the ECU to wake up and get the CEL to illuminate so I can start the vehicle is hooking up the charger and getting the system up to like 12.8v or more.. Its left me stuck too many times now and even with having a ton of experience working on these cars I don't know where to begin.. My only guess is some sort of ECM power relay being worn out or something but I dont know.. Anyone care to throw a hypothesis out there? Thank you First off you may want to consider proof reading that again... Second have you tested the ECU on the bench and see if the problem is with the ECU itself, shouldn't have an issue connecting even with as low as 6-7v. Unplug the ECU and check power at the plug and resistance to ground. I had a customer with a similar issue and the ECU box was flooded due to clogged drains, ended up having corroded ground wires Title: Re: ECU Doesn't Seem to Wake Up Without Excessive Battery Voltage Levels Post by: royce5950 on May 21, 2023, 01:55:02 AM I have not checked the ECU box yet I am going outside to check it now and I wouldnt be surprised if there were a bit of water in there because the side of the ECU box cracked and I repaired it with plastic JB weld however I always was weary that it could still allow moisture to get in somehow because I didnt think it was going to hold up the same.. will let you know what I find. As far as functionality I did a MPPS read, rewrote the ECU with MPPS and used a stock flash for a couple days then I flashed back to my 8E0910115P 19psi file and still issue persists regardless.. Eeprom is untouched.. I had a crack in my windshield last year and I know for a fact that moisture made its way behind the dash and even during heavy rain I would go around a corner and my feet would get wet because water would fall on them.. But I got the windshield replaced about a year ago and I made sure no moisture was puddled up anywhere.. So water could definitely be an issue somewhere..
Title: Re: ECU Doesn't Seem to Wake Up Without Excessive Battery Voltage Levels Post by: adam- on May 21, 2023, 11:37:20 AM Could log ECU voltage...
Title: Re: ECU Doesn't Seem to Wake Up Without Excessive Battery Voltage Levels Post by: nyet on May 21, 2023, 02:45:49 PM bad wiring
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