ADT Emissions Control & Environmental Compliance 2 — Questions and Answers
Question 1: An Audi's NOx sensor reads abnormally high values after SCR catalyst replacement. What is the most likely cause?
- Faulty AdBlue pump
- Incorrect NOx sensor wiring polarity
- SCR catalyst not reaching operating temperature
- Upstream NOx sensor measuring pre-catalyst exhaust (Correct answer)
Correct answer: Upstream NOx sensor measuring pre-catalyst exhaust
The upstream NOx sensor measures raw exhaust before the SCR, so high readings there are normal; the downstream sensor should show reduction.
Question 2: What EPA regulation requires Audi technicians to use refrigerant recovery equipment before servicing an A/C system?
- Clean Air Act Section 608 (Correct answer)
- Clean Air Act Section 609
- CARB Title 13
- SAE J2788
Correct answer: Clean Air Act Section 608
Section 608 of the Clean Air Act mandates refrigerant recovery to prevent venting of ozone-depleting and greenhouse substances during stationary equipment service.
Question 3: A TFSI engine shows a P0299 (turbocharger underboost) code alongside elevated HC emissions. What component should be inspected first?
- EGR valve
- Charge air cooler for oil contamination (Correct answer)
- Catalytic converter substrate
- Crankcase ventilation system
Correct answer: Charge air cooler for oil contamination
A leaking charge air cooler allows oil to enter the intake tract, raising HC emissions and reducing boost pressure simultaneously.
Question 4: Audi's Active Noise Cancellation system is unrelated to emissions, but which on-board system shares its CAN bus messaging to coordinate emissions reduction at high load?
- Engine Sound Actuator (ESA)
- Electrically controlled wastegate (Correct answer)
- Active engine mount
- Acoustic valve in exhaust
Correct answer: Electrically controlled wastegate
The electrically controlled wastegate shares CAN data with the engine ECU to manage boost and combustion efficiency, directly influencing NOx and HC outputs.
Question 5: When performing a leak-down test on an Audi 2.0 TFSI, you find 25% leakage on cylinder 3 with air escaping into the crankcase. What is the emissions impact?
- Increased CO2 only
- Elevated HC due to oil burning from blow-by (Correct answer)
- Reduced NOx due to lower combustion temperature
- No emissions impact
Correct answer: Elevated HC due to oil burning from blow-by
Blow-by past piston rings allows unburned fuel and combustion gases to enter the crankcase, increasing HC emissions when vented through the PCV system.
Question 6: What is the purpose of the secondary air injection pump on early Audi V8 engines during cold start?
- To pressurize the fuel system
- To inject fresh air into the exhaust stream to oxidize HC and CO before the catalyst warms up (Correct answer)
- To reduce turbo lag
- To power the EGR valve during warm-up
Correct answer: To inject fresh air into the exhaust stream to oxidize HC and CO before the catalyst warms up
Secondary air injection supplies oxygen to the exhaust manifold, enabling exothermic oxidation of HC and CO emissions before the catalyst reaches light-off temperature.
Question 7: An Audi B9 A4 with 2.0 TDI fails opacity (smoke) testing at idle. Scan data shows normal boost and rail pressure. What should be checked next?
- Glow plug circuit
- EGR cooler for coolant intrusion causing white smoke
- DPF differential pressure sensor
- Fuel injector return flow (Correct answer)
Correct answer: Fuel injector return flow
Excessive injector return flow indicates worn injector internals causing over-fueling, which produces black smoke at idle without affecting rail pressure readings significantly.
ADT Emissions Control & Environmental Compliance 2
An Audi's NOx sensor reads abnormally high values after SCR catalyst replacement.
What is the most likely cause?