Practice Test #3 1 Flashcards

A technician is testing a battery and finds it reads 12.4 volts at rest but drops to 9.8 volts during cranking. The battery passes a load test at 50% of CCA rating. What is the MOST likely cause of the hard-start condition?

Answer: The battery terminals have high-resistance corrosion reducing available voltage

A resting voltage of 12.4 V indicates a reasonably charged battery, but a severe voltage drop during cranking points to a high-resistance connection rather than a bad battery or starter. Corroded or loose terminals create enough resistance to collapse available voltage under load, causing slow or no-start conditions even when the battery itself passes a capacity test.

During a cooling system inspection, a technician finds the upper radiator hose collapses when the engine cools down after shutdown. What is the MOST likely cause?

Answer: A failed radiator cap that cannot hold vacuum relief open

As the engine cools, the coolant contracts and creates a vacuum inside the system. The radiator cap has a vacuum (return) valve that opens to allow coolant from the overflow reservoir to refill the system. If that valve sticks closed, the vacuum collapses the softest hose — typically the upper radiator hose — instead of drawing coolant back in.

A front-wheel-drive vehicle produces a rhythmic clicking noise that increases with vehicle speed and is loudest during sharp turns. The noise disappears when driving straight. What component is MOST likely at fault?

Answer: A worn or failed outer CV (constant velocity) joint

Outer CV joints are stressed most during turns because the joint operates at a steeper angle. A clicking or popping noise that appears during turns and increases with speed — but disappears on straight roads — is the classic symptom of a worn or dry outer CV joint that has lost its grease due to a torn boot.

A vehicle's OBD-II scanner shows a P0420 code — 'Catalyst System Efficiency Below Threshold.' Which test would BEST confirm the catalytic converter is the root cause before replacing it?

Answer: Compare upstream and downstream oxygen sensor waveforms with a lab scope

P0420 is set when the ECM detects that the downstream (post-cat) O2 sensor is switching at a rate similar to the upstream (pre-cat) sensor, meaning the converter is not storing and releasing oxygen efficiently. Using a lab scope to overlay both sensor waveforms lets the technician see this directly: a good converter shows a nearly flat downstream signal while the upstream signal swings rapidly.

A technician measures excessive play in a rack-and-pinion steering gear. The tie rod ends, ball joints, and wheel bearings are all within specification. What is the MOST likely cause of the steering looseness?

Answer: Excessive internal wear in the rack-and-pinion unit itself

If all external steering linkage components (tie rod ends, ball joints, wheel bearings) are within spec but excessive play remains, the source must be internal to the rack-and-pinion unit — typically worn teeth on the rack or the pinion, or worn bushings inside the housing. The rack-and-pinion assembly would need to be rebuilt or replaced.

An engine oil analysis report shows a high concentration of coolant in the oil. The cooling system pressure test holds steady and no white exhaust smoke is observed. Where is the coolant MOST likely entering the oil?

Answer: A failed intake manifold gasket on an engine with a coolant-crossover passage

Many V6 and V8 engines route coolant through the intake manifold to warm the throttle body or EGR components. A failed intake manifold gasket at a coolant-crossover passage allows coolant to seep directly into the intake port and then into the oil via the drain-back passages — without producing white smoke or failing a cooling system pressure test, because the leak is below combustion pressure.