Ecu won't run fuel pump
 

I'm helping a friend with his 2002 TT Quattro convertible. I've found that the ecu does not trigger the fuel pump relay. It doesn't run to prime the fuel system when the door is opened, or when the motor is started. (gave it some fuel to get it started momentarily). Also found the pump does not produce any fuel pressure if powered externally. We're ordering a new fuel pump to solve that part of the problem. Wiring and fuses check out ok.

What would cause the ecu not to turn on the fuel pump?

Accident detection kills the fuel pump. Certainly from an airbag deployment. Probably other things can cause this as well.

When I opened the fuel tank I found both sides were empty despite the fuel gauge reading almost half a tank. I added fuel and performed a ecu reset. After that the motor started right up.

Time to have the instrument cluster rebuilt.

Tanin Auto Electronix

and

Module Master

both have been highly recommended by fellow posters here.

I'll pass that along to the owner. Thanks for the help.

Never heard of a cluster not causing a fuel pump to turn on. Not to say it doesn't have problems of its own though. The fuel gauge issue could certainly be a cluster issue. It could also be a sending unit problem too.

Assuming you checked all of the relays too? It could be the ECU since that is what triggers the fuel pump relay to turn on.

If the pump doesn't power on when you test it directly then it sounds like you already found the problem.

The cluster definitely has problems. More than just the gas gauge not working properly. It was definitely the ecu reset that got the fuel pump turning on again. The pump did run when powered directly and is picking up fuel again. The owner is happily driving his car every day despite the display issues, which he'll no doubt get fixed when he gets a bit of extra cash available. Thanks for the help.

Great to hear!

Here is a link for when they are ready.
Audi A4 A6 S4 TT Allroad Gauge Cluster Rebuild

We also have some helpful and information videos on that page too specific to Audi TT.

Thanks, I'll definitely pass that along.