Non Starter - Troubleshooting Help Required!

[prj]

Considering he took out the dash, the problem is most likely somewhere in the wiring.
A simple continuity test with a multimeter on these might show the problem:
Test ECU PIN 49 to G28 (Speed sensor) signal pin
Test ECU PIN 47 to G4 (Crankshaft position sensor) signal pin
Test ECU PIN 48 to G28 GROUND pin and G4 GROUND pin.

Make sure ECU PIN 49 is not short to GND (measure resistance between PIN 49 and chassis).

[S2central.net]

I do wonder if the dash removal disturbed some cables - it shouldnt really if it was done cleanly and properly - there is a chance that someone disturbed the plugs under the main fusebox.

Another to check is that G4 and G28 are connected to the correct plugs.

G4 is the crank reference sensor - you get a massive AC spike from that once every crank rotation - this connects to the cable with a BLACK coloured plug at the bulkhead.

G28 lines up to count flywheel teeth - this has a GREY coloured plug at the bulkhead.

Look at the diagram on top of page 7 attached to be 100% sure on positioning.

Also - unplug the two white connectors that supply power to the coil packs - you should see 12V on all 5 wires when the key is on.

[UrS4boy]

...Another to check is that G4 and G28 are connected to the correct plugs.

G4 is the crank reference sensor - you get a massive AC spike from that once every crank rotation - this connects to the cable with a BLACK coloured plug at the bulkhead.

G28 lines up to count flywheel teeth - this has a GREY coloured plug at the bulkhead.

Look at the diagram on top of page 7 attached to be 100% sure on positioning.

Also - unplug the two white connectors that supply power to the coil packs - you should see 12V on all 5 wires when the key is on.

This photo shows the connectors on an UrS6 but they should be the *similar* on an ABY. Point is Audi colour-coded the harness and ancilliary plugs so all you have to to is make sure the colours match when you make the connections. If the G28 is plugged into the black harness connector instead of the grey, then the ECU will have bad G4 and G28 signals.

[S2central.net]

Positions are different but colours are the same.

[UrS4boy]

Positions are different but colours are the same.

Edited to delete "same" and replace with "similar" and add "Point is Audi colour-coded the harness and ancilliary plugs so all you have to to is make sure the colours match when you make the connections. If the G28 is plugged into the black harness connector instead of the grey, then the ECU will have bad G4 and G28 signals."

[newsh]

No after market alarm is fitted, I had the Clifford Concept 50 removed.

I have remembered an intermittent problem it has, when I start the car sometimes the engine just turns over quite slowly without actually firing up. If you then switch off and try again it fires up. Is it possible this is the root of the problem?

Ok, at least there's no alarm/immob confusing things. Perhaps it could be a bad ignition switch, again a multimeter will tell you if the 12v is getting to the ecu.

[prj]

He said in other thread FP Relay is getting energized.
If it is, ecu is definitely getting G28 signal, probably getting G4 signal, for sure has correct voltages, and what's lacking is the hall sensor signal, because his wiring (as much as I understood) is defect in that area.