Parasitic Current Drain

Parasitic Draw Test:

TOOLS REQUIRED:
J 39200 Digital Multimeter or equivalent
J 38758 Parasitic Draw Test Switch

NOTE: The parasitic draw test switch should never be turned to the "OFF" position with the engine running, or damage could occur to the attached ammeter or the vehicle electrical system.

Important
^ The switch knob on the J 38758 is marked "ON" and "OFF." When the switch knob is in the "ON" position, the circuit is closed and electrical current may pass through the switch. When the switch knob is in the "OFF" position, the circuit is open and electrical current may not pass through the switch.
1. Remove the battery ground (negative) cable from the battery negative terminal. Refer to "Battery Ground (Negative) Cable Disconnect/Connect". Battery Ground (Negative) Cable Disconnect/Connect
2. Install the J 38758 male end to the battery negative terminal.
3. Turn the J 38758 knob to the "OFF" position.
4. Install the battery ground (negative) cable to the female end of the J 38758.
5. Turn the J 38758 knob to the "ON" position.
6. Road test the vehicle and activate all of the accessories (radio, A/C, etc.).
7. Stop the vehicle. Turn the ignition switch to the "OFF" position and remove the ignition key.
8. Set the digital multimeter (DMM) to the 10 ampere scale and connect it to the terminals on test switch tool.
9. Turn the J 38758 knob to the "OFF" position to allow the current to flow through the DMM.
10. Underhood lamp. Slowly lower the hood while observing the underhood lamp. If the underhood lamp shuts off while lowering the hood, it is working properly and should now be disconnected. If the underhood lamp does not shut off, it is most likely the source of parasitic current drain.
11. Ensure that the interior lights are off and all doors closed.
12. Wait at least 60 seconds. Check the current reading. If the current reading is at or below 2 amperes, turn the J 38758 knob to the "ON" position (to maintain continuity in the electrical system) and switch the DMM down to the two ampere scale for a more accurate reading. Turn the J 38758 knob "OFF". Wait 10 minutes. Check and record the current reading.

NOTE: Always turn the parasitic draw test switch knob to the "ON" position before removing each fuse to maintain continuity in the electrical system and to avoid damaging the ammeter due to accidental overloading (I.E.: opening door to change fuse etc.).

13. Note the reserve capacity rating for the vehicle's battery.
- Divide the reserve capacity number by four.
- Compare this number to the ampere reading taken in step ten.
- The parasitic current drain should not exceed this number.
- Example: If the battery has a reserve capacity rating of 100 minutes, the current drain should not exceed 25 milliamps.
14. If the vehicle has an acceptable amount of current drain and the vehicle battery was weak or failed a load test, check the charging system for proper operation.
15. If the vehicle has an unacceptable amount of current drain, remove each fuse one at a time until the current drain falls to an acceptable level. This will indicate which circuit is causing the drain. In some rare cases, a "non-fused" circuit or component, such as a generator, may be the cause of excessive current drain.

Important
^ Repeat the parasitic current drain procedure after any repair has been completed to ensure that the current drain has returned to an acceptable level.

16. When the cause of the excessive current drain has been located and repaired, remove the J 38758 and connect the battery ground (negative) cable to the battery.Then refer to to diagnose exactly which part of the suspect circuit is causing the drain.