Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGeneral Electrical/Electronic System DiagnosisMedium
A technician is performing a parasitic drain test. After connecting an ammeter in series with the battery negative cable, the technician observes a 500 mA (0.5 Amp) draw. The vehicle's specifications state a maximum allowable parasitic drain of 50 mA. Which of the following is the NEXT step the technician should take?
- ADisconnect the battery to prevent further drain.
- BBegin removing fuses one by one while monitoring the ammeter.
- CStart the engine to see if the draw clears.
- DCheck the battery's state of charge.
Show answer & explanationAnswer & explanation
Correct answer: B. Begin removing fuses one by one while monitoring the ammeter.
A 500 mA draw is significantly higher than the allowable 50 mA, indicating an excessive parasitic drain. The next logical step to isolate the source of the drain is to systematically remove fuses (or disconnect circuit breakers) one by one while continuously monitoring the ammeter. When the draw drops significantly, the last fuse removed (or circuit disconnected) identifies the problematic circuit.
Why the other options are wrong
- A. While disconnecting the battery prevents further drain, it doesn't help locate the source of the problem.
- C. Starting the engine would interrupt the test and not help identify the source of the drain.
- D. The battery's state of charge is a result of the drain, not the cause, and checking it won't help find the source of the drain.
Parasitic Drain Isolation
The process of identifying the specific circuit responsible for an excessive electrical current draw when the vehicle is off, typically by systematically disabling circuits.
- Ammeter connected in series with battery.
- Vehicle must be in 'sleep' mode (all systems off).
- Fuses are removed one by one to pinpoint circuit.
Memory trick: High drain is a thief, pull fuses for relief.