Engine Diagnostics Flashcards
7 cards from real ASE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Engine Diagnostics flashcards as text
Right after a timing belt replacement, the engine sets a camshaft/crankshaft position correlation code. What is the most likely cause?
Answer: Timing belt installed one or more teeth off
A correlation code after belt work usually means the cam and crank are out of time.
During a power balance test, disabling cylinder 4 causes almost no rpm drop while the others drop about 100 rpm. What does this mean?
Answer: Cylinder 4 is contributing little power
A cylinder that already makes little power causes almost no rpm change when disabled.
A spark plug has a white, blistered insulator tip. What does this indicate?
Answer: Overheating from a lean mixture or a plug heat range that is too hot
Blistered white insulators result from excessive combustion chamber temperatures.
A spark plug is covered in wet, black, oily deposits. What is the most likely cause?
Answer: Oil entering the cylinder through worn rings or valve guides
Wet oily deposits mean engine oil is getting into the combustion chamber.
An ECT sensor reports -40°F on a fully warm engine. Which symptom is most likely?
Answer: Rich running, poor fuel economy, and black smoke
The PCM thinks the engine is cold and adds extra fuel, causing a rich condition.
An engine cranks but will not start, with no spark and no injector pulse, and the tachometer reads zero while cranking. What is the most likely cause?
Answer: Faulty crankshaft position sensor
Without a crank position signal, the PCM cannot fire the coils or pulse the injectors.
When performing a cranking compression test, which step is correct?
Answer: Hold the throttle wide open and disable fuel and ignition
A wide-open throttle allows full airflow, and disabling fuel and ignition prevents flooding and coil damage.