Battery Electrical Drain/Parasitic Load Test

Tools Required

• J 38758 Parasitic Draw Test Switch
• J 39200 Digital Multimeter
• A Fused Jumper Wire

1. Disconnect the negative battery cable. Refer to Battery Negative Cable Disconnect/Connect Procedure .
   
   
2. Install the male end of the J 38758 (1) to the negative battery terminal.
   
   
3. Turn the test switch OFF (1).
4. Connect the negative battery cable (2) to the female end of the test switch.
   
   
5. Turn the test switch ON (1).

Notice

Do not turn the parasitic draw test switch to the OFF position with the engine running. Damage will occur to the vehicle's electrical system.

6. Road test the vehicle. Activate all accessories, including the air conditioning system and radio.
7. Turn OFF the ignition switch. Remove the key.

Important

This allows the electronically timed components to power down, preventing false parasitic drain readings.

8. Wait 15 minutes before continuing the test.
   
   
9. Connect the fused jumper wire (1) to the terminals of the test switch.
10. If the fuse does not fail, the J 39200 can be installed. A current of less than 10 amps is present.
    
    
11. Turn the test switch ON (1).
12. Remove the fused jumper wire.
    
    
13. Set the J 39200 to the 10A scale (1).

Important

If an ammeter other than the J 39200 is used, ensure that the vehicle does not have a high current drain that would damage the ammeter when connected to the circuit.

14. Connect the J 39200 to the terminals (2) of the test switch.
    
    
15. Turn the test switch OFF (1). Current is now flowing through the ammeter option of J 39200 .
16. Wait one minute.
17. Wait until the current reading is 2 amps or less.
    
    
18. Turn the test switch to ON (1).
19. Switch the J 39200 from the 10A setting to the 2A setting.
    
    
20. Turn the test switch to OFF (1).
21. Read the current in milliamps. This is the parasitic drain value.
22. Note the battery reserve capacity. Refer to Battery Usage .
23. Divide the battery reserve capacity by 4, this will be the parasitic drain number.
24. The parasitic drain number should not exceed ¼ of the battery's reserve capacity.
25. If the parasitic drain number exceeds ¼ of the battery's reserve capacity go to step 27.
    
    
26. Turn the test switch ON (1).

Notice

The test switch must be in the ON position when removing the fuses in order to maintain continuity in the electrical system. This avoids damaging the digital multimeter due to accidental overloading, such as a door being opened to change a fuse.

27. To find the source of the excessive load perform the following:

A. Remove the courtesy lamp fuse. Note the J 39200 reading.

B. If the parasitic load is still excessive start removing the remaining fuses.

C. Keep the courtesy lamp fuse out during diagnosis, so the door can remain open.

28. Continue removing the fuses one at a time, starting with the fuses that are hot all the time. When the voltage drops across the J 39200 , note the last fuse removed. The current drain comes from the circuit or circuits protected by that fuse.
29. Repair the circuit and perform the parasitic load test again to verify the repair.
    
    
30. Connect the negative battery cable. Refer to Battery Negative Cable Disconnect/Connect Procedure .