If the vehicle exhibits a low or dead battery after an overnight period, or discharges over a period of 2 or 3 days, the electrical system should be tested for an excessive electrical drain. This is referred to as “parasitic current drain.”
If a battery needs recharging and no cause is evident, test the vehicle for excessive parasitic current drain.
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. When the battery is disconnected to install anammeter, etc., the excessive current drain may not occur once circuit continuity is restored. Even though cycling the ignition key to the RUN and then to the OFF position may at times cause such a drain to recur, there may be drains that will not recur unless the vehicle systems are reactivated in a road test. Since the ignition switch must not be rotated to the ACCESSORY, RUN, or START position with an ammeter installed between the battery terminal and the battery cable, a current drain test tool must be used as described in the following procedures.
Before starting this procedure, make sure the ignition switch is in the “LOCK” position, all electrical accessories are turned off, and the doors are closed.
CURRENT DRAIN TEST
Terminal Adapters (GM P/N 12303040)
J 38758 Parasitic Draw Test Switch
J 39200 Digital Multimeter
NOTICE: The parasitic draw test switch should 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 at the main battery.
• The main battery will be wired from the positive battery terminal to the starter motor.
2. Install the male end of J 38758 to the negative battery terminal (figure 8).
3. Turn 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.
From this point on, electrical continuity must be maintained in the ground circuit to the battery, either through the J 38758 (in the “ON” position) or through the ammeter.
8. Some components, such as PCM’s, 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.
• 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 the multimeter 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 two amps, turn the test switch to the “ON” position (to maintain continuity in the electrical system) and switch down to the two 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 “Specifications” at the end of this section. Divide this number by 4. Compare this to the digital 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. If a vehicle is equipped with an auxiliary battery, use only the reserve capacity of the main battery.
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. Start with fuses that are hot at all times. Refer to the Driveability, Emissions, and Electrical Diagnosis Manual. To remove the fuse, the door must be opened. This may cause a high enough current draw to damage the multimeter. To protect the meter without disrupting electrical continuity, turn the test tool to the “ ON” position before opening the door. Then remove the courtesy lamp fuse. Note the meter reading. If the parasitic load is still excessive, start removing the other fuses, one at a time. Leave the courtesy lamp fuse out during diagnosis so the vehicle door can be left open.
Perform steps 10 through 12 each time a fuse is removed.
15. Removing the PCM fuse should cause a drop of less than 10 milliamps.
• If the drop is more than 10 milliamps, check the orange wires for a short to ground. Also check the components connected to the orange wires.
Refer to the Driveability, Emissions, and Electrical Diagnosis Manual.
* If there is no drop in the milliamp reading, the PCM is not drawing current. Refer to the Driveability, Emissions, and Electrical Diagnosis Manual.
16. Repeat the parasitic current drain procedure after any repair has been completed.
17. 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.
Negative battery cable bolt to 15 N-m (11 Ibs. ft.).