Audi TT Turbocharging and Forced Induction Systems 3

Question 1

On the Audi TT Mk1 1.8T engine, what turbocharger model is factory installed in the 225 hp variant?

Accepted Answer

K04 turbocharger

Answer

The Audi TT 225 hp (1.8T BAM engine) uses the larger K04 turbocharger compared to the K03 unit found in lower-output variants.

Question 2

What is 'boost creep' and what component failure commonly causes it on the Audi TT?

Accepted Answer

Uncontrolled boost rise beyond target caused by a stuck or undersized wastegate

Answer

Boost creep occurs when the wastegate cannot flow enough exhaust gas to limit boost, causing it to rise above the ECU's target — potentially causing knock or damage.

Question 3

On the Audi TT, which cooling system supports the water-to-air intercooler loop independently of the main engine cooling circuit?

Accepted Answer

A separate low-temperature auxiliary coolant circuit with its own electric pump

Answer

The Mk2 TT's charge air cooling uses a dedicated low-temp auxiliary loop with a separate electric coolant pump, independent from the main high-temp engine circuit.

Question 4

What is the consequence of running an Audi TT turbo engine with restricted or coked oil return lines?

Accepted Answer

Oil backup into the turbo center housing causing seal failure and oil consumption

Answer

If oil cannot drain freely from the turbo, it backs up in the center section, creating pressure that forces oil past the shaft seals into the intake or exhaust.

Question 5

When inspecting an Audi TT turbocharger for shaft play, what is the acceptable axial (in/out) play specification?

Accepted Answer

Up to 0.05 mm is acceptable; greater indicates bearing wear

Answer

A small amount of axial play up to approximately 0.05 mm is normal, but excessive play indicates worn thrust bearings requiring turbo replacement.

Audi TT - Certified Audi TT Specialist Practice Test

Audi TT - Certified Audi TT Specialist Practice Test

Audi TT Turbocharging and Forced Induction Systems 3