Engine Performance & Diagnostics Flashcards

A TDI shows a high soot load and the DPF differential pressure sensor reads high. The customer drives only short city trips. What is the best first action?

Answer: Perform a stationary or road-test regeneration with a scan tool

Short trips prevent passive and active regeneration, so a forced regeneration is the proper first step.

On a TDI, which measurement helps identify a faulty injector at idle?

Answer: Injector quantity deviation (cylinder balance) in mg/stroke

Quantity deviation shows how much each cylinder's fuel is being corrected, which reveals weak or over-delivering injectors.

A smoke machine is most useful for finding which type of fault?

Answer: Intake vacuum leaks and EVAP system leaks

Smoke pushed into the intake or EVAP system comes out at leak points so they can be seen.

A MAF sensor that reads too little airflow would cause fuel trims to do what?

Answer: Go positive, especially at higher load

The ECM meters fuel for less air than is actually entering, so the mixture goes lean and trims add fuel, mostly at higher airflow.

In VW component naming, which part is N75?

Answer: Boost pressure control (wastegate) solenoid valve

N75 controls wastegate actuator pressure to regulate boost.

A wet compression test raises a low cylinder reading a lot. What does this indicate?

Answer: Worn piston rings

The oil temporarily seals the rings, so a large pressure rise points to ring or cylinder wear.

Before flashing an engine control module (J623) software update with ODIS, what is required?

Answer: Connect a stable battery charger/power supply

A voltage drop during flashing can corrupt the module, so a stable power supply is required.