Found THEE ground fault that kills the A3 dash cluster gauges

[AHood]

I found out the bad ground that has cut out all the gauges on my A3 cluster. I thought i had a bad cluster or something, but turns out the bad ground is in the engine bay right by the coolant sensor there are two wire terminals that go on a ground stud right next to what appears to be the main engine wire harness plug. one terminal has two wires the other has one. if the two wire terminal is faulty (not grounding) your cluster gauges wont work. hope this helps someone. I did a lot of searching and alot of people said oh you have a bad ground "somewhere" well this is "where".

 

[paramedick]

You mean this one......

 

[AHood]

ok theres 3 terminals. on mine 2 were wired together. well basically if one of those is bad your dash will not work.

 

[vdub_15]

Was your cluster completely not working or just in-accurate?

 

[AHood]

the gauges were not working at all.

 

[G60ING]

Was your cluster completely not working or just in-accurate?

I had an issue where everything on my TDI Corrado (passat B4 cluster with mk3 engine) worked great except my fuel level gauge would be off the charts when the tank was full. After recieving some chips to test in my car the fuel gauge worked correctly. I went back to my original chips but I disconnected my positive battery terminal while swapping the various chipsets. Now my fuel gauge reads correctly. There was no noticeable corrosion on the positive battery terminal.

fyi the fuel level does not get routed to the ecu so you can't blame that either.

 

[sprstu]

No Dash Gauges, car runs and starts great. 98 Jetta TDI, 217xxx. Story:

Last night I replaced my glow plug harness and glow plugs, the job took about an hour. I Started by disconnecting the battery, knowing I was going to work with an electrical system and all. I unplugged all the harnesses surrounding the glow plug/temp/fuel shut off to get better access. I cut and soldered in the new glow plug harness wires and put everything back together. Thats when everything started to go wrong. First was the non-start. Then the CEL. I read codes for short to ground on fuel shut off, coolant temp, and glow plugs. I then took everything apart and put it back together, seemingly all was well. I checked for connectivity across all the wires in the harness, all good. Still no start.
I then jumped the fuel shut off and we had ignition. Bad ground. I cleaned the main grounding point (as pictured above) put everything back together, car started great, but no gauges. I then checked with a test light to make sure all three grounds were good, testing the grounding post showed good, then on the body of each wire showed good. Still no gauges.
Car starts and runs perfect, the clock and odometer show when the key is 'off' but once it goes into ACC or run they go out. No tach, fuel or temp. All warning lights show across the bottom. CEL reads temp sender open to POSITIVE as well.

Is there any other grounding points than the one above?

 

[rdkern]

I believe there's a main one under/near the battery, and if like the B4, one on the other side of the boost pipe from the battery, near the washer fluid tank.

Look carefully.

 

[tdidieselbobny]

Just polished up the grounds under the battery tray.It is held down by 4-10mm head bolts,and the PS reservoir allen bolt(5mm)-the one ground had 3 wires going to it,the other was a single line from battery. The nut heads were either 11mm or 12mm that hold the wires.

 

[sprstu]

I took out the battery tray and found the other grounds, I sanded them and cleaned the area on and around the bolt they fit on. I also re-cleaned the ground from the pic above and no change, if anything its worse again because I dont think my fuel shut off is opening, again. I will take it apart again tomorrow and cry a little more inside.
Side note, I pulled fuses 21 and 22, waited 30 seconds and put them back in, the temp and fuel gauge did a full sweet and came back to the bottom but did not activate with the key, neither did the Tach.

 

[sprstu]

I have found that it was no and is not the wiring or the grounds, all are in god working order. Upon disconnection of the round harness and coupler I broke a tab and thus preventing the harness from seating properly. There is a small connection in the harness but once a large power supply, like the glow plugs firing, is sent through it the system shorts out due to weak grounds.
This problem throws 7 different codes all at once,
short to ground; glow plugs, coolant temp sensor, fuel shut off valve
short to positive; coolant temp sensor
glow plug fault code and fuel 109 code.

Now comes the hard part, finding that round coupler piece part number 3a0 973 103