Operation CHARM: Car repair manuals for everyone.
Home >> GMC Truck >> 2000 >> C 6500 TopKick V8-7.4L VIN D >> Repair and Diagnosis >> Starting and Charging >> Battery >> Testing and Inspection >> Component Tests and General Diagnostics >> Battery Electrical Drain/Parasitic Load (Current Draw)

Battery Electrical Drain/Parasitic Load (Current Draw)




Battery Electrical Drain/Parasitic Load (Current Draw)

Tools Required
* J 38758 Parasitic Draw Test Switch
* J 42000 Digital Multimeter

Before starting this procedure, turn the engine control switch to the LOCK position, turn off all electrical accessories, and close the vehicle's doors.

Caution: Refer to Battery Disconnect Caution in Cautions and Notices

Notice: J 38758 should never be turned to the OFF position, with the engine running or damage could occur to the vehicle's electrical system.

1. Disconnect the negative battery cable at the battery. Refer to Battery Cable Replacement (Negative Cable to Engine) Battery Cable Replacement (Negative Cable to Engine)Battery Cable Replacement (Positive Cable) Service and RepairBattery Cable Replacement (Negative Cable to Frame) Battery Cable Replacement (Negative Cable to Frame).




2. Use the following procedure in order to install the J 38758 to a Side Terminal Battery:

1. Install the male end of the J 38758 to the negative battery terminal.
2. Turn the knob of the J 38758 to the OFF position.
3. Install the negative battery cable to the female end of the J 38758 .




3. Use the following procedure in order to install the J 38758 to a Top Threaded Post Battery:

1. Remove the terminal bolt from the battery cable end of the J 38758 .
2. Thread a terminal adapter (GM P/N 12303040) onto the negative terminal post of the battery (1).
Important: Verify that the bottom of the adapter firmly contacts the pad or base of the battery post.


3. Install the battery cable end of the J 38758 over the threaded end of the terminal adapter (GM P/N 12303040).
4. Thread a second terminal adapter over the first.
5. Turn the knob of the test switch to the OFF position.
6. Use a pair of terminal adapters in order to install the negative battery cable to the female end of the J 38758 .

4. Turn the test switch to the ON position.
5. Road test the vehicle and activate all accessories including the radio and air conditioning.
6. Turn the ignition switch to the OFF position and remove the key.

Important: Electrical continuity in the ground circuit to the battery must be maintained from this point forward. Use the J 38758 (in the ON position) or the J 39200 in order to maintain electrical continuity.


7. Some components, including PCMs, have timers that draw several amps of current when the components cycle down. This condition may cause an incorrect parasitic current drain reading. Wait 15 minutes in order to allow the above components to power down before continuing the test.

Important: If using a digital multimeter other than the J 39200 , ensure that the vehicle does not have excessive current drain. Excessive current drain may damage the multimeter when the multimeter is installed. Use the following procedure in order to test the current drain level:


1. Connect a jumper wire with an in-line 10 amp fuse to the J 38758 terminals.

2. Turn the J 38758 to the OFF position.

3. Wait 10 seconds.

4. Inspect for a blown fuse.

If the fuse does not blow, the current draw is less than 10 amps and the J 39200 may operate safely.

5. Turn the J 38758 to the ON position.

Turning the J 38758 to the ON position before installing the J 39200 maintains continuity in the electrical system.

6. Remove the fused jumper wire.

7. Install the J 39200 .


8. Set the J 39200 to the 10 amp scale and connect the multimeter to the J 38758 .
9. Turn the J 38758 to the OFF position. Current now flows through the J 39200 only.
10. Wait at least 60 seconds in order to observe the current reading.
If the current reading is at or below 2 amps, turn the test switch to the ON position (in order to maintain continuity in the electrical system) and switch the J 39200 to the 2 amp scale for a more accurate reading.
11. Turn the J 38758 to the ON position.
12. Measure the reading in milliamps, if necessary.
13. Refer to Battery Specifications in Battery Usage [1][2]Battery in order to determine the reserve capacity of the battery.
14. Divide the reserve capacity value by 4 and compare the result to the J 39200 reading.
The current drain reading should not exceed the value determined above. Example: If a battery has a reserve capacity of 100 minutes, the current drain should not exceed 25 milliamps.

NOTICE: Always turn the test switch knob to the ON position before removing each fuse in order to maintain continuity in the electrical system and to avoid damaging the digital multimeter due to accidental overloading, such as opening a door to change a fuse.

15. If the current draw is excessive, remove the system fuses one at a time until the draw returns to a value less than or equal to the specified value.
In order to protect the J 39200 without disrupting electrical continuity, turn the test switch to the ON position before opening the door.
16. Start with fuses that are hot at all times. Refer to Power Distribution Schematics Power Distribution Schematics in Wiring Systems.
17. Remove the courtesy lamp fuse and observe the J 39200 reading.
18. If the parasitic load remains excessive perform the following steps:

1. Removing the other fuses, one at a time.
2. Leave the courtesy lamp fuse out during diagnosis so the vehicle door can be left open.
3. Observe the J 39200 reading each time a fuse is removed.

19. The PCM fuse should cause a drop of less than 10 milliamps when removed.
20. If the drop is more than 10 milliamps, inspect the PCM wiring for a short to ground. Also, inspect the components connected to the wires. Refer to the related schematics for the system being worked on.
21. Repeat the parasitic current drain test after the condition has been located and repaired. The vehicle could have more than one parasitic current drain.
22. When the cause of the excessive current draw has been located and repaired, remove the J 39200 the J 38758 and the terminal adapters.
23. Connect the negative battery cable. Refer to Battery Cable Replacement (Negative Cable to Engine) Battery Cable Replacement (Negative Cable to Engine)Battery Cable Replacement (Positive Cable) Service and RepairBattery Cable Replacement (Negative Cable to Frame) Battery Cable Replacement (Negative Cable to Frame).

pro multis · About Operation CHARM