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 (0.5A) draw. All doors are closed, and the ignition is off. The technician then begins pulling fuses one by one from the fuse box. When fuse F10 (radio/infotainment) is removed, the draw drops to 50 mA (0.05A). What does this indicate?
- AThe vehicle has an acceptable parasitic draw.
- BThe ammeter is faulty and providing an incorrect reading.
- CThe radio/infotainment system is the source of an excessive parasitic draw.
- DFuse F10 is blown, causing the draw to drop.
Show answer & explanationAnswer & explanation
Correct answer: C. The radio/infotainment system is the source of an excessive parasitic draw.
A parasitic draw of 500 mA (0.5A) is excessive (most vehicles should be below 50 mA after modules go to sleep). When removing fuse F10 causes the draw to drop significantly to 50 mA, it isolates the radio/infotainment system as the source of the excessive drain, bringing the total draw down to an acceptable level.
Why the other options are wrong
- A. 500 mA is an excessive draw; acceptable draw is typically below 50 mA.
- B. The consistent drop in current when the fuse is pulled indicates the ammeter is functioning correctly.
- D. If fuse F10 were blown, the radio/infotainment system would not be drawing current, and the initial 500 mA draw would not have been present.
Parasitic Draw Isolation
The process of systematically identifying the source of an excessive parasitic current draw by removing fuses or disconnecting components until the draw drops to an acceptable level.
- Ammeter connected in series with the battery.
- Target draw is typically below 50 mA after modules sleep.
- Removing a fuse that causes a significant drop identifies the problematic circuit.
Memory trick: Fuse Pull Reveals the Silent Power Thief's Lair.