Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGeneral Electrical/Electronic System DiagnosisMedium
A technician is diagnosing an intermittent starting issue on a vehicle. The starter motor clicks once but does not crank the engine. A voltage drop test is performed on the battery positive cable from the battery post to the starter motor's battery terminal while attempting to crank. The multimeter reads 0.5 volts during the click. What does this reading indicate?
- AA good battery positive cable connection.
- BA discharged battery.
- CA faulty starter solenoid.
- DExcessive resistance in the battery positive cable.
Show answer & explanationAnswer & explanation
Correct answer: A. A good battery positive cable connection.
A voltage drop of 0.5 volts or less on a high-current circuit like the battery positive cable during cranking is generally considered acceptable. This indicates that the cable itself and its connections have low resistance and are not the primary cause of the starting issue.
Why the other options are wrong
- B. A discharged battery would cause low system voltage, but the voltage drop test measures resistance in the cable, not battery charge.
- C. While a faulty starter solenoid could cause the click-no-crank, the voltage drop test on the positive cable is evaluating the cable's integrity, not the solenoid directly.
- D. Excessive resistance would result in a significantly higher voltage drop (e.g., several volts).
Voltage Drop Test (High Current)
Measures the voltage lost across a wire or connection under load, indicating resistance in that path. For high-current circuits, small drops are normal.
- Performed with the circuit under load.
- Measures resistance of the wire/connection itself.
- Acceptable drop varies by circuit, but typically <0.5V for main power cables.
Memory trick: Little drop is good, big drop is bad, for the starter to crank, don't be sad.