Hi,

I have a 2008 Q7 4.2 TDI S-Line.

A few months ago it displayed an error: Turbo Control Unit faulty. The check engine light came on, the glow plug indicator flashed, and it went into limp mode. I took it to the dealer, who plugged in their diagnostic tool, and they said it's the left side turbo. But, after clearing the error it was 100% for about four months.

Then, it happened again. I took it back again, but this time the error would not clear. The dealer's advice was to completely replace the left side turbo at huge expense.

I figured it's worth a try to repair it first, so a local mechanic swapped out the control unit, which the had imported from Netherlands. They had it programmed and tested at the dealer, so it should be OK. However, the same error keeps being displayed.

They tried everything they could think of, including cleaning all wire connectors and having the turbo pressure tested. They even took the new control unit out and replaced it with a second one. No luck. For some reason the error remains.

It is now back at the dealer who wants to start replacing parts without knowing what the core problem is. I am afraid costs might run await with such a trail-and-error approach, and seeing that it is an old car it wouldn't make much sense to spend more than the car is worth.

Please help! I am out of ideas.