Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGeneral Electrical/Electronic System DiagnosisHard
A technician is diagnosing an intermittent starting issue on a vehicle. The starter motor sometimes clicks but does not crank the engine. The battery has been tested and is fully charged. When the issue occurs, a voltage drop test across the starter solenoid's main power terminal to the battery positive post shows 0.1V. A voltage drop test from the starter motor's ground connection to the battery negative post shows 0.8V. Which of the following is the MOST likely cause of the intermittent starting issue?
- AHigh resistance in the starter motor's ground circuit.
- BA short circuit in the starter motor's windings.
- CInsufficient current from the battery to the starter.
- DA faulty starter motor solenoid.
Show answer & explanationAnswer & explanation
Correct answer: A. High resistance in the starter motor's ground circuit.
The voltage drop test on the ground side of the starter circuit shows 0.8V, which is significantly higher than the acceptable range (typically less than 0.2V). This indicates excessive resistance in the ground circuit, which can prevent the starter motor from drawing enough current to crank the engine, leading to a 'click but no crank' symptom. The 0.1V on the positive side is acceptable.
Why the other options are wrong
- B. A short in the windings would likely cause excessive current draw, potentially blowing a fuse or damaging the battery, and wouldn't be directly indicated by these voltage drop readings.
- C. While true that insufficient current is reaching the starter, the voltage drop test specifically identifies the high resistance on the ground side as the cause, not a general battery issue (since the battery is good).
- D. The solenoid itself might be clicking, but the high ground side voltage drop points to a different issue preventing cranking.
Starter Ground Circuit Resistance
Excessive resistance in the starter motor's ground path can prevent sufficient current flow, leading to 'click, no crank' symptoms.
- Ground circuit resistance should be very low (typically < 0.2V drop).
- High resistance restricts current, reducing motor torque.
- Often caused by corroded connections or loose cables.
Memory trick: Ground's High Drop Steals the Starter's Crank Power.