If the vehicle exhibits a low or dead battery after an overnight period, or discharges over a period of 2 or 3 days and no cause is evident, the electrical system should be checked for an excessive electrical drain. The cause of the excessive unintended current drain is referred to as a parasitic load. One or more on-board solid-state control modules, such as the PCM, may at some time exhibit a failure mode that causes a high parasitic drain on the vehicle's battery. Another source of parasitic drain could be an unnoticed load such as a glove box lamp which remains on at all times.

Testing for a parasitic drain requires a special tool because the excessive current drain may not occur after the battery is disconnected to install an ammeter. Cycling the ignition key to the RUN and then to the OFF position may cause such a drain to recur, but there may be drains that will not recur unless the vehicle systems are reactivated in a road test. The ignition switch must not be rotated to the START position with an ammeter installed between the battery terminal and the battery cable, but the special tool enables the vehicle to be driven to assure that all vehicle systems are ready for testing.

Tools Required

Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

1. Disconnect the negative battery cable.
2. Ensure that the ignition switch is in LOCK, all electrical accessories are turned OFF, and the doors are closed.



3. Install the male end of the J 38758 to the negative battery terminal.
4. Turn the J 38758 test switch to the OFF position.
5. Connect the negative battery cable to the female end of the J 38758 test switch.
6. Turn theJ 38758 test switch to the ON position.

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.

7. Road test the vehicle while activating all the accessories, such as the radio and the air conditioning.
8. Turn the ignition switch to the LOCK position and remove the key. Turn all electrical accessories off. Close the doors of the vehicle to prevent a current draw for the interior courtesy lamps.
9. In order to avoid a false reading, wait 15  minutes for all components to power down before continuing this test
10. Before connecting the ammeter, use the following procedure to determine whether or not the current drain is less than 10 amps:

10.1.

Connect a jumper wire with an in-line 10-amp fuse or circuit breaker to the terminals of the J 38758 test switch.

10.2.

Turn the J 38758 test switch to the OFF position.

10.3.

Wait 10 seconds.

11. If the fuse in the jumper wire does not blow, turn the J 38758 test switch ON, set the J 39200 to the 10-amp scale and connect the digital multimeter to the J 38758 test switch, and then remove the jumper wire. If current is greater than 10 amps, use a test lamp instead of an ammeter.

Important: Always turn the J 38758 test switch to the ON position between tests. The ON position allows current to flow through the battery cable. If the test switch is left in the OFF position between tests, the ammeter could be damaged due to accidental overloading. An example of an accidental high current load would be opening the door of the vehicle (to change a fuse), and turning on the interior courtesy lamps. If the test switch is in the OFF position when the door is opened, all current for the lamps would flow through the ammeter, and the meter may be damaged if it is set in the low range.

12. Remove the fuses one at a time, and install each one after it is tested. Perform the following steps each time a fuse is removed:

12.1.

Turn the test switch to the OFF position which forces all current to flow through the meter.

12.2.

Wait at least 60 seconds. Check the current reading. If the reading is at or below 2 amps, turn the test switch to the ON position in order to maintain continuity in the electrical system while switching to the 2 amp scale for a more accurate reading. Turn the test switch to the ON position between tests.

12.3.

The parasitic draw is typically under 60  milliamperes. If the ammeter drops to an acceptable reading after a fuse is removed, the circuit causing the drain has been identified.

12.4.

Install the fuse for the circuit which is causing the excessive drain. Using the schematic as a guide, disconnect the components of the faulty circuit one at a time until the faulty component is located. If the fuse for the interior courtesy lamps is removed, the door of the vehicle can be open during the test procedure without damaging the ammeter while it is set in the low range.

13. When the cause of excessive current draw has been located and repaired, remove the current drain test switch and connect the negative battery cable to the negative battery terminal.