Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsStarting System Diagnosis and RepairHard
A technician observes that a starter motor is drawing 300 amps during a current draw test, but the engine is cranking normally. The OEM specification for this starter is 150-200 amps. What does this indicate?
- AThe battery is overcharging the starter motor.
- BExcessive resistance in the starter motor circuit.
- CThe starter motor has internal short circuits.
- DAn issue with the engine, such as excessive mechanical drag.
Show answer & explanationAnswer & explanation
Correct answer: D. An issue with the engine, such as excessive mechanical drag.
If the starter motor is drawing significantly more current than specified while still cranking the engine normally, it suggests that the engine itself is harder to turn over than it should be. This could be due to internal engine issues causing excessive mechanical drag, such as tight bearings or incorrect timing.
Why the other options are wrong
- A. Batteries do not 'overcharge' starter motors; they supply current based on the starter's demand and circuit resistance. Overcharging typically refers to alternator output.
- B. Excessive resistance in the starter motor circuit would cause a *lower* current draw and slow or no cranking, not higher current with normal cranking.
- C. Internal short circuits in the starter motor would typically cause excessive current draw, but the motor would likely struggle to turn or not turn at all, not crank normally.
Starter Current Draw Diagnosis
Measuring the current consumed by the starter motor during cranking to assess its internal condition and the mechanical effort required to turn the engine.
- High current draw with normal cranking suggests engine mechanical issues.
- High current draw with slow/no cranking can indicate internal starter shorts.
- Low current draw with slow/no cranking suggests high circuit resistance or weak battery.
Memory trick: High amps, normal crank, means the engine's a mechanical prank!