VW Emissions Control & Environmental Compliance 2

Question 1

Which VW-specific scan tool parameter indicates the NOx storage catalyst has reached its sulfur poisoning threshold?

Accepted Answer

Adaptation value exceeding 100%

Answer

When the NSC adaptation value exceeds 100%, the ECM flags sulfur saturation and initiates a desulfation request.

Question 2

On a VW TDI with AdBlue, what is the consequence of allowing the DEF tank to run completely empty?

Accepted Answer

Engine power is reduced by 25% and a no-restart interlock activates after the next key-off

Answer

EPA regulations require a no-restart interlock when SCR DEF fluid is absent, and VW implements a torque reduction followed by a start-inhibit after refill confirmation.

Question 3

A technician reads an active fault P2002 (DPF efficiency below threshold) on a VW Golf TDI. Which measurement most directly confirms DPF restriction?

Accepted Answer

Differential pressure across the DPF exceeding specification at a given exhaust mass flow

Answer

The ECM calculates DPF efficiency using the differential pressure sensor readings relative to exhaust mass flow; high differential pressure at normal flow confirms restriction.

Question 4

What is the primary purpose of the lean NOx trap (LNT) on VW GDI engines during highway driving?

Accepted Answer

To store NOx during lean operation and reduce it during brief rich purge cycles

Answer

The LNT stores NOx as nitrates during lean operation and releases and reduces them during timed rich regeneration events.

Question 5

A VW 2.0 TSI engine fails a state I/M test for high HC at idle. The ECM shows no DTCs. Which component failure is MOST likely?

Accepted Answer

Crankcase ventilation valve stuck open causing oil vapor bypass

Answer

A stuck-open PCV valve allows unmetered oil vapor into the intake, raising HC emissions without necessarily setting a DTC.

(VW) Volkswagen Certified Technicians Practice Test

(VW) Volkswagen Certified Technicians Practice Test

VW Emissions Control & Environmental Compliance 2