ASE T1 Domain 6: Fuel, Air Induction, and Exhaust Systems Diagnosis and Repair

A vehicle exhibits poor fuel economy and the engine runs rich. However, the O2 sensor readings are normal. What could be the most likely cause?

During a road test, a technician notes that the vehicle lacks power during acceleration. A backpressure test on the exhaust system shows higher than normal readings. What is the MOST likely cause?

A vehicle with port fuel injection has higher than normal short-term fuel trim values at idle, but they normalize at higher speeds. What is the MOST likely cause?

After replacing the throttle body on a vehicle, the engine idles erratically and sets a DTC for the idle air control system. Technician A says the throttle body gasket could be leaking. Technician B says that the idle air control valve may need to be relearned. Who is correct?

A vehicle has a rough idle and a "rotten egg" smell coming from the exhaust. The engine's performance improves at higher speeds. What is the MOST likely diagnosis?

A vehicle with a turbocharged engine is experiencing low power output and the check engine light is on. There are codes related to the turbocharger boost pressure. Technician A suggests checking the intercooler system for leaks. Technician B suggests inspecting the turbocharger wastegate for proper operation. Who is correct?

If a vehicle with sequential fuel injection is running lean and has misfires on multiple cylinders, what should a technician check FIRST?

When diagnosing an electronic throttle control ETC system, a technician finds DTCs indicating low voltage at the motor control circuit. What could be the cause?

A vehicle's engine has an intermittent surge at cruising speeds. The fuel trims are normal, and there are no vacuum leaks. What could be the next best component to inspect?

A gasoline direct injection (GDI) engine is experiencing rough idling and misfires. There are no DTCs present. What diagnostic step should be prioritized?