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, they connect an ammeter in series with the negative battery cable. After allowing the vehicle to 'go to sleep' for 30 minutes, the ammeter reads 150 milliamperes (mA). What does this reading indicate?
- AA short circuit in the vehicle's wiring.
- BA normal parasitic draw for a modern vehicle.
- CA faulty ammeter reading due to improper connection.
- DAn excessive parasitic draw that needs to be diagnosed.
Show answer & explanationAnswer & explanation
Correct answer: D. An excessive parasitic draw that needs to be diagnosed.
A parasitic draw of 150 milliamperes (0.15 amps) is considered excessive for most modern vehicles. A normal parasitic draw should typically be 50 mA or less, and often closer to 20-30 mA. An excessive draw like 150 mA would significantly drain the battery over several days or weeks.
Why the other options are wrong
- A. While a short circuit can cause excessive draw, a parasitic draw test specifically measures current when the vehicle is off and should be 'asleep.' A direct short would likely cause a much higher current draw and possibly blow a fuse.
- B. A normal parasitic draw is typically 50 mA or less, so 150 mA is considered excessive.
- C. Assuming the ammeter is connected correctly, 150 mA is a real measurement, not necessarily an improper reading. The interpretation of the value is key.
Parasitic Draw
Parasitic draw is the normal and abnormal current draw from the battery when the ignition is off and the vehicle is 'asleep'.
- Normal draw is typically 20-50 mA (0.02-0.05 amps).
- Excessive draw can drain the battery, especially if the vehicle sits for extended periods.
- Requires an ammeter connected in series with the battery cable.
Memory trick: Fifty mA or less, battery blessed.