ASE G1 Auto Maintenance and Light RepairElectrical/Electronic SystemsMedium
A technician is performing a parasitic draw test. With the ignition off and all accessories off, the multimeter reads 500 mA. What is the MOST appropriate next step in diagnosing this excessive draw?
- AStart the engine and check the charging system voltage.
- BDisconnect the battery and charge it fully.
- CBegin pulling fuses one at a time while observing the multimeter.
- DTurn on the headlights to see if the draw increases.
Show answer & explanationAnswer & explanation
Correct answer: C. Begin pulling fuses one at a time while observing the multimeter.
A parasitic draw of 500 mA (0.5 Amps) is significantly higher than the acceptable range (typically 20-50 mA). To locate the source of this draw, the technician should systematically disconnect circuits by pulling fuses one at a time while monitoring the multimeter. When the draw drops significantly, the last fuse pulled indicates the circuit containing the fault.
Why the other options are wrong
- A. Checking the charging system is unrelated to an excessive parasitic draw when the vehicle is off.
- B. Charging the battery addresses the symptom (dead battery) but does not diagnose the cause of the parasitic draw.
- D. Turning on the headlights would intentionally increase the draw, making it harder to diagnose the existing parasitic draw, and is not a diagnostic step for this issue.
Parasitic Draw Diagnosis
Diagnosing an excessive parasitic draw involves measuring current with a multimeter and systematically isolating circuits by removing fuses until the draw drops to an acceptable level.
- Acceptable draw is typically 20-50 mA.
- Multimeter connected in series.
- Fuses pulled one-by-one to isolate.
Memory trick: Parasitic Draw: Current leaking out when it shouldn't.