No start, no glow plug light

[Greasy_Bastard]

I have a 1999 Audi A4 TDI, AFN engine. It is the 99 facelift model.

A couple weeks ago I hopped in the car but it didn't start. Cranks fine. The glow plug light doesn't turn on when I turn the key. And no clicking sound is heard when the key is turned to On-position.

I checked all the fuses I could find. There were a couple big ones under the steering wheel and in the ECU box. All seemed fine.

Next I changed a couple relays, 219(the equivalent of 109 in this model), 202(glow plug/injection pump relay). No difference.

I tried to disconnect the battery negative wire, reached into the ecu box and wiggled all the relays, reached around the ecu to push the connectors in.

Tried to disconnect the coolant temperature sensor, turned on power, waited for 20s and tried to start. Wouldn't catch.

Today I tried to check the fault codes with VCDS I borrowed from a friend. Couldn't connect to engine module and not much else - only central locking, abs brakes, radio, immobilizer.

Im starting to think there is a problem with the ECU or the wiring to it.

I went through some threads. Some managed to solve the problem by changing the 109 relay, some discovered a wire had gone bad somewhere.

Anyone have any experience with a similar problem?

 

[Seatman]

Maybe try and find a pin pin out diagram for the ecu, see if you can find the power and check it's actually reaching the ecu.

Also can the ecu get wet in the A4? I've seen it in an A6, ecu was soaked through due to a blocked drain, caused all kinds of issues. A good dry out and all was well again.

 

[Greasy_Bastard]

That's a good idea to check the pins that supply the power. It wouldn't be surprising if there is some corrosion damage in there. It's hard to keep all the leaves and stuff out of that small space where the box sits.

 

[Greasy_Bastard]

I checked the ecu box, it was clean and dry. Changed the ignition switch, the old one looked brand new. No effect, didn't get the glow plug light and car didn't start.

So I removed all the fuses from the fuse box. Then replaced them and got the glow plug light and car started nicely.

Now the central locking doesn't work, but that has been an ongoing problem in the wintertimes.

Im somewhat puzzled what caused this no start condition. Have to play around with the fuses to see if it returns. Something strange with the electrical system.

I even found the correct wiring diagrams from www.vag-hub.com. Can't really decipher them yet.

 

[Seatman]

I checked the ecu box, it was clean and dry. Changed the ignition switch, the old one looked brand new. No effect, didn't get the glow plug light and car didn't start.

So I removed all the fuses from the fuse box. Then replaced them and got the glow plug light and car started nicely.

Now the central locking doesn't work, but that has been an ongoing problem in the wintertimes.

Im somewhat puzzled what caused this no start condition. Have to play around with the fuses to see if it returns. Something strange with the electrical system.

I even found the correct wiring diagrams from www.vag-hub.com. Can't really decipher them yet.

Must be a fuse connection not being as tight as it could be or something, I've had plugs like that. Unplug and reseat and everything is good again. . No idea which though, whenever I look up fuse diagrams they tend to be wrong for whatever car I have lol.