Current Drain Testing

TOOLS REQUIRED:
Terminal Adapters GM P/N 12303040
J 38758 Parasitic Draw Test Switch J 39200 Digital Multimeter

CAUTION: Refer to "Service Precautions".

NOTICE: The parasitic draw test switch must never be turned to the "OFF" position with the engine running or damage could occur to the vehicle electrical system.

1. Remove the negative battery cable.
^ On a diesel-equipped vehicle with two batteries, disconnect the negative battery cable at the main battery in the engine compartment on the driver's side.
2. Install the male end of J 38758 to the negative battery terminal.
3. Turn the knob on the test switch to the "OFF" position.
4. Install the negative battery cable to the female end of the test switch.
5. Turn the test switch to the "ON" position.
6. Road test the vehicle while activating all accessories, such as the radio and air conditioning.
7. Turn the ignition switch to the "OFF" position and remove the key.

Important: From this point on, electrical continuity must be maintained in the ground circuit to the battery, either through J 38758 in the "ON" position or through the ammeter.

8. Some components, such as a PCM or VCM, have timers that draw several amps of current while they cycle down. This can give a false parasitic drain reading. Wait 15 minutes for these components to power down before continuing this test.

Important
^ Before performing Step 9, if a digital multimeter is being used other than J 39200, make sure the vehicle does not have a high current drain that might damage the multimeter when it is installed. This can be done using the following procedure:
- Connect a jumper wire with an in-line 10 amp fuse to the terminals on the test switch. Then turn the test switch to the "OFF" position. Wait about 10 seconds. If the fuse does not blow, current draw is less than 10 amps, and the digital multimeter can be used safely. Before removing the fused jumper wire and installing the multimeter, turn the test switch to the "ON" position.

9. Set J 39200 to the 10 amp scale and connect it to the terminals on the test switch.
10. Turn the test switch to the "OFF" position to allow current to flow through the meter.
11. Wait at least 60 seconds. Check the current reading. If the current reading is at or below 2 amps, turn the test switch to the "ON" position (to maintain continuity in the electrical system) and switch down to the 2 amp scale for a more accurate reading when the test switch is reopened.
12. Take the reading in milliamps.
13. Find the reserve capacity of the battery in "Battery Specifications." Divide this number by 4. Compare this to the multimeter reading. The current drain reading should not exceed this number. (Example: If a battery has a reserve capacity of 100 minutes, the current drain should not exceed 25 milliamps. If the vehicle has a diesel engine with 2 batteries, add the reserve capacities together and divide this total by four).

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

14. If current draw is too high, remove system fuses one at a time until the draw returns to a value less than or equal to the specifications.
15. Repeat the parasitic current drain procedure after any repair has been completed.
16. When the cause of excessive current draw-has been located and repaired, remove the meter, test switch and terminal adapters and connect the negative battery cable to the negative battery terminal.