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themadscientist
02-24-2013, 09:14 PM
Working on a 97 AEB auto. Customer said car started running like crap suddenly and they parked it. Hooked up VCDS and it has a bunch of short to ground/low input codes for MAF, evap purge valve, N75, etc. Fuses 29 and 34 were shot. I went through the engine wiring with a fine tooth comb and found no broken wires. I disconnected the harness at the bulkhead under the ECU and the main Red/green wire has no continuity to ground on the engine side of things, but the cabin side does. I traced it to the fuse, and when I pull the fuse, there's no continuity to ground on the red/green wire side of the fuse, but there IS continuity to ground on the other side of the fuse terminal where it turns into a solid green wire. Elsa doesn't show me much on that wire. I traced it back to the fuel pump relay, tried unplugging the relay, but it was still shorting. there's also a solid green wire right under the fuel pump relay that bolts to a terminal, which also shows continuity to ground.

If you understood that, please help.

themadscientist
02-24-2013, 09:29 PM
Edit; scratch that. I think I found my the issue. Please feel free to chime in with any relevant info.

ianwpb
02-24-2013, 10:01 PM
My stupid printer won't let me scan anything because I'm out of black ink, so I'll do my best here...

Fuel pump relay
- Terminal 3 is Ro/Bl to ECU
- T87a is Gn/Sw to F34 (15A). From the fuse it's Gn/Ge to the injectors. Injector 1 to ECU is Sw/Gn, 2 is Br/Bl, 3 Br/Gn, 4 Sw/Li.
- T87f the Gn wire goes to F29 (20a) - 2 Ro/Gn wires split off. 1 goes to the LDP. The other goes to the N75 (to ECU Ge/Ws), N80 (to ECU Li), both 02 sensors, and the MAF.
- T87f Gn/Ws to F28 (15a) Gn/Ge to Fuel pump

As for the MAF -
Pin 1 Br ground to E25 ("Engine wire harness ground connection 1"). It shares the Ground with the ICM. I don't know much about the 1.8t but this jumps out at me..
Pin 2 Ge to ECU T80/12
Pin 3 Ro/Gn
Pin 4 Gn to ECU T80/13

There's more to the diagram obviously, but as far as fuse 29 and 34 go, this is it. Hope this helps.

themadscientist
02-24-2013, 10:24 PM
My stupid printer won't let me scan anything because I'm out of black ink, so I'll do my best here...

Fuel pump relay
- Terminal 3 is Ro/Bl to ECU
- T87a is Gn/Sw to F34 (15A). From the fuse it's Gn/Ge to the injectors. Injector 1 to ECU is Sw/Gn, 2 is Br/Bl, 3 Br/Gn, 4 Sw/Li.
- T87f the Gn wire goes to F29 (20a) - 2 Ro/Gn wires split off. 1 goes to the LDP. The other goes to the N75 (to ECU Ge/Ws), N80 (to ECU Li), both 02 sensors, and the MAF.
- T87f Gn/Ws to F28 (15a) Gn/Ge to Fuel pump

As for the MAF -
Pin 1 Br ground to E25 ("Engine wire harness ground connection 1"). It shares the Ground with the ICM. I don't know much about the 1.8t but this jumps out at me..
Pin 2 Ge to ECU T80/12
Pin 3 Ro/Gn
Pin 4 Gn to ECU T80/13

There's more to the diagram obviously, but as far as fuse 29 and 34 go, this is it. Hope this helps.

Thanks, I just looked it up on a different computer, it shows the relay pinout. The solid green wire is the only one in question (87F) it also has /DTI next to it. I'm pretty sure it still had continuity to ground when I unplugged the relay, so I'll probably just double check everything, run an overlay and call it good.

rwoodland
02-24-2013, 10:27 PM
believe there is a shared ground at rear of engine compartment bolted to firewall. Ive run into the nut coming looses. also had one with front end colision which pinched harnes at rear f valve cover, also had bad relays. Find shared circuit, ground/componet affected sensors and circle on diagram and star there, 10 year audi tech on recent carreer change with all diagrams in my garage and not right in front of me. find common denominators and eliminate easist to access. I love wiring diag. tick is to stayfocusd take time to understand circuits and eliminate easiest to access. good luck if you ned more assistance will be glad to grab my diagrams and help.

themadscientist
02-24-2013, 10:40 PM
believe there is a shared ground at rear of engine compartment bolted to firewall. Ive run into the nut coming looses. also had one with front end colision which pinched harnes at rear f valve cover, also had bad relays. Find shared circuit, ground/componet affected sensors and circle on diagram and star there, 10 year audi tech on recent carreer change with all diagrams in my garage and not right in front of me. find common denominators and eliminate easist to access. I love wiring diag. tick is to stayfocusd take time to understand circuits and eliminate easiest to access. good luck if you ned more assistance will be glad to grab my diagrams and help.

I appreciate it. I ruled out any shorts in the engine bay by going through the entire harness in question, then finally disconnecting it from it's bulkhead just behind and below the ECM. Once it that section of the engine harness was disconnected from the rest of the vehicle, it showed no continuity to ground. That's when I started digging into the dash. I pulled the fuse for the circuit in question and only the powering side (solid green wire) still showed a short. I removed the relay and it still showed a short. I'm looking at the factory diagram No 84/3 - motronic control unit, fuel pump relay, air mass meter, injectors.