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  1. #1
    Established Member Two Rings SacSantorin's Avatar
    Join Date
    Aug 18 2015
    AZ Member #
    349773
    Location
    Almost Canada, WA

    Advice Needed: Can't connect to ECU & No Start

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    Hi guys

    I could use some advice as how to proceed with an issue. I'm pretty strong with working on the car mechanically, but electronics are foreign and scare me. I'm having a no start issue after a bad jump where the donor vehicle got the leads crossed. I currently have no spark or fuel, and can't talk to the ECU with vagcom or my handheld scanner. The check engine light is not coming on with the key on engine off position which is telling me there is an issue with the ECU. I'm also not getting any power to the ECU & fuel pump fuses in the driver side fuse box (fuses 28, 29, 32, 34) when testing with a multimeter with key on engine off position. I have power to other fuses in the box.

    My first thought was either the ECU relay or the Fuel Pump relay, but after throwing parts at that it seems to be something else. Any ideas on another relay or fuse that could be causing this? I've done some searching but haven't found any similar issues with not having power to the fuses. It's a 2000 ATW B5 A4 1.8TQ.

    Thanks in a advanced!
    2000 Audi A4 1.8T | Santorin Blue | Frankenturbo F21L Mixed Flow | Motoza 550cc Tune | Custom 2.5'' Exhaust w/ Milltek Downpipe | 3'' MAF Housing | 3" Ebay Testpipe | CX Racing FMIC | B6 5 Spoke Wheels | ECS Boost Guage | OEM RS4 Grill

  2. #2
    Active Member Two Rings
    Join Date
    Jun 08 2017
    AZ Member #
    400768
    Location
    london

    So you put the + to the - and the - to the +?

    Did you check all the fuses? If they are all good then you’ve probably fried the ecu.

    Do you have access to another ecu to rule that out?


    Sent from my iPhone using Tapatalk

  3. #3
    Veteran Member Four Rings walky_talky20's Avatar
    Join Date
    Jun 30 2008
    AZ Member #
    30427
    Location
    Erie, Pennsylvania

    Sounds like you are on the right track. You have only a few possibilities:

    A - ECU is not getting constant power / ground
    B - ECU is not seeing the key turn on (ignition switch)
    C - ECU is getting everything just fine, but it is smoked (faulty ECU)

    There are just a few things to do to check for these:

    **Step 0: Pull an accurate Engine wiring diagram so you aren't flying blind here.**

    A - Unplug the ECU and check that all power and grounds are present
    B - Unplug the ECU and check that ignition switch power signal is present
    C - If A and B check out fine, it's C. Swap in a used ECU for $50 and give it a shot.
    ^Don't listen to this guy, he's not even a mechanic.
    2001 Laser Red A4 1.8TQM, 5-Speed Swapped, 4.11 Final Drive, APR 93, R8 coil packs, Labree HFC & DP, 2.5" Exhaust, ST Coilovers, 034 RSB, A8 Brakes Front & Rear, 18" RS4 Reps
    2006 Passion Red Volvo V50 T5 AWD 6MT
    "You need to know what you are doing...Its like a rainbow jungle in there." - Redline380

  4. #4
    Active Member Two Rings
    Join Date
    May 29 2017
    AZ Member #
    400260
    Location
    Fort Collins, CO

    For the most part you are shorting out your battery when you cross jumpers like that.
    First thing to do is disconnect the battery from the car, charge it, then do a load test to make sure the battery is still good.
    Maybe voltage is not high enough to turn the ECU on because you melted a few plates inside your battery.
    If it's good then check all your fuses.
    If you are lucky you just have some blown fuses.

    If you are not lucky you may have a dead ECU and/or alternator (may no longer charge if regulator was blown).
    If you are really really not lucky you fried the computer in your dash cluster.
    If you are really really really not luckly you fried wires in your wiring harness (Audi likes to use small gauge wires...)....and you won't be able to get a replacement from Audi....because you could buy a new used Audi for the cost of the new harness.

  5. #5
    Established Member Two Rings SacSantorin's Avatar
    Join Date
    Aug 18 2015
    AZ Member #
    349773
    Location
    Almost Canada, WA

    Thank you everyone for your insight and advice. This community has always been incredibly supportive and has a wealth of knowledge on these cars and one of the main reasons I will always own an Audi.

    At this point, I'm thinking that the ECU might be fried. I'm currently trying to source a used cheap ECU to swap in and test it, but since I bought a new car today (not because of this problem, I've been shopping for the last few months) so this is no longer my daily and I can take my time chasing this problem. I'll be sure to update this thread with anything I find for people with similar issues in the future.


    Thank you all!
    2000 Audi A4 1.8T | Santorin Blue | Frankenturbo F21L Mixed Flow | Motoza 550cc Tune | Custom 2.5'' Exhaust w/ Milltek Downpipe | 3'' MAF Housing | 3" Ebay Testpipe | CX Racing FMIC | B6 5 Spoke Wheels | ECS Boost Guage | OEM RS4 Grill

  6. #6
    Veteran Member Four Rings walky_talky20's Avatar
    Join Date
    Jun 30 2008
    AZ Member #
    30427
    Location
    Erie, Pennsylvania

    Do you have an engine diagram so you can verify power and grounds to check at the ECU location? If you need one, just drop me a PM with your email address.
    ^Don't listen to this guy, he's not even a mechanic.
    2001 Laser Red A4 1.8TQM, 5-Speed Swapped, 4.11 Final Drive, APR 93, R8 coil packs, Labree HFC & DP, 2.5" Exhaust, ST Coilovers, 034 RSB, A8 Brakes Front & Rear, 18" RS4 Reps
    2006 Passion Red Volvo V50 T5 AWD 6MT
    "You need to know what you are doing...Its like a rainbow jungle in there." - Redline380



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