ADT Powertrain & Engine Management Systems 3 — Questions and Answers
Question 1: On an Audi 2.0 TDI with a variable-geometry turbocharger (VTG), what actuator controls the position of the variable vanes?
- Vacuum-operated diaphragm actuator or electric servo motor (Correct answer)
- Wastegate solenoid valve only
- Boost pressure control valve on the compressor housing
- Intake manifold flap motor
Correct answer: Vacuum-operated diaphragm actuator or electric servo motor
VTG turbochargers on Audi TDI engines use either a vacuum diaphragm or an electric actuator to rotate the variable guide vanes and control boost across the RPM range.
Question 2: An Audi Q7 4.2 FSI shows cylinder-specific misfire codes on cylinders 5 and 6 only. Compression and leakdown tests are within spec. What should be checked NEXT?
- Fuel pressure regulator
- Injector spray pattern and high-pressure fuel delivery to bank 2 (Correct answer)
- Ignition coils on cylinders 5 and 6
- Valve timing on bank 2
Correct answer: Injector spray pattern and high-pressure fuel delivery to bank 2
On bank-specific misfires with good compression, the high-pressure fuel supply circuit (rail pressure, injector function) for that bank should be evaluated next.
Question 3: What is the purpose of the 'Leak Detection Pump' (LDP) in the Audi EVAP system?
- Pump fuel vapors into the intake manifold under boost conditions
- Pressurize the fuel vapor system to detect small leaks as small as 0.5 mm (Correct answer)
- Recirculate purge air back to the fuel tank
- Control fuel vapor flow rate to the charcoal canister
Correct answer: Pressurize the fuel vapor system to detect small leaks as small as 0.5 mm
The LDP pressurizes the EVAP system and monitors pressure decay to detect leaks as small as 0.5 mm in diameter, satisfying OBD-II evaporative monitor requirements.
Question 4: During an Audi S4 3.0 TFSI oil consumption test, how many miles must the vehicle be driven before re-checking oil level per Audi's approved procedure?
- 500 miles
- 1,000 miles (Correct answer)
- 1,500 miles
- 3,000 miles
Correct answer: 1,000 miles
Audi's approved oil consumption test requires the vehicle to be driven 1,000 miles under normal operating conditions before rechecking the oil level to determine consumption rate.
Question 5: A fault code P0087 (fuel rail/system pressure too low) is stored on an Audi 1.8 TFSI. After confirming low rail pressure with a gauge, which component should be tested FIRST?
- High-pressure fuel pump (HPFP) and its cam-driven follower
- Low-pressure fuel pump (LPFP) delivery volume and pressure (Correct answer)
- Fuel pressure regulator valve on the rail
- Injector return flow rate
Correct answer: Low-pressure fuel pump (LPFP) delivery volume and pressure
Low rail pressure diagnosis begins with the low-pressure side; insufficient LPFP delivery is the most common root cause and must be confirmed before condemning the HPFP.
Question 6: On Audi engines using the EA839 engine family, what is the function of the 'cylinder on demand' (COD) system's oil pressure valves?
- Increase oil flow to the HPFP lobe
- Hydraulically lock the rocker arms for deactivated cylinders, holding valves closed (Correct answer)
- Reduce main bearing oil pressure during cylinder deactivation
- Control variable camshaft timing on deactivated cylinders
Correct answer: Hydraulically lock the rocker arms for deactivated cylinders, holding valves closed
Oil pressure control valves supply or cut hydraulic pressure to rocker arm locking pins, which either couple or decouple the cam followers to deactivate valve motion on selected cylinders.
Question 7: When using ODIS-E (Engineering) for an Audi long-term fuel trim (LTFT) analysis, a positive LTFT value of +18% at idle indicates what engine condition?
- The engine is running rich and the ECM is reducing fuel
- The engine is running lean and the ECM is adding fuel to compensate (Correct answer)
- Exhaust gas recirculation is excessive
- The high-pressure fuel pump is over-delivering
Correct answer: The engine is running lean and the ECM is adding fuel to compensate
A positive LTFT means the ECM is adding fuel beyond the base map to correct a lean condition, which can be caused by vacuum leaks, low fuel pressure, or faulty MAF.
ADT Powertrain & Engine Management Systems 3
On an Audi 2.0 TDI with a variable-geometry turbocharger (VTG), what actuator controls the position of the variable vanes?