Assessment and Evaluation Flashcards

On a VW TSI engine, which ODIS measured value is most useful for judging fuel trim health?

Answer: Short-term and long-term fuel trim (mixture adaptation) values

Mixture adaptation values show how much the ECM is correcting fueling, which reveals lean or rich conditions.

A long-term fuel trim of +20% at idle that drops near 0% at higher RPM most likely points to what?

Answer: A vacuum (unmetered air) leak

A vacuum leak has the biggest effect at idle, where the unmetered air is a larger share of total airflow.

What is the purpose of a cylinder leak-down test compared with a compression test?

Answer: It shows where compression is being lost

A leak-down test pinpoints the leak path, such as the valves, rings, or head gasket.

A compression test shows one cylinder low, and adding oil raises the reading a lot. What is the likely cause?

Answer: Worn or stuck piston rings

Oil seals the rings for a short time, so a big rise in compression points to ring wear.

When evaluating a 12 V AGM battery in a VW with start/stop, which test is most reliable?

Answer: A conductance or load test with the tester set to the AGM battery type

AGM batteries are sealed, so a conductance or load test set to the correct battery type gives an accurate result.

After replacing the battery on many modern VWs, what step is typically required?

Answer: Adapt or code the new battery in the battery monitoring control module

The battery energy management system has to be told about the new battery so it charges correctly.

What is the best way to evaluate whether a suspension noise comes from a worn control arm bushing?

Answer: Inspect for cracking or excess movement while prying with the vehicle loaded on the ground

Inspecting bushings under load and checking for movement shows deterioration directly.