Battery Electrical Drain/Parasitic Load Test
BATTERY ELECTRICAL DRAIN/PARASITIC LOAD TEST
TOOLS REQUIRED
J 38758 Parasitic Draw Test Switch Tool
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.
For Vehicles equipped with OnStar (RPO UE1) with Back Up Battery:
The Back Up Battery is a redundant power supply to allow limited OnStar functionality in the event of a main vehicle battery power disruption to the VCIM (OnStar module). Do not disconnect the main vehicle battery or remove the OnStar fuse with the ignition key in any position other than OFF. Retained accessory power (RAP) should be allowed to time out or be disabled (simply opening the driver door should disable RAP) before disconnecting power. Disconnecting power to the OnStar module in any way while the ignition is On or with RAP activated may cause activation of the OnStar Back-Up Battery (BUB) system and will discharge and permanently damage the back-up battery. Once the Back-Up Battery is activated it will stay on until it has completely discharged. The BUB is not rechargeable and once activated the BUB must be replaced.
NOTE:
^ 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.
^ 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.
1. Disconnect the battery negative cable from the battery negative terminal.
2. Install the male end of the J 38758 to the battery negative terminal.
3. Turn the J 38758 knob to the OFF position.
4. Install the battery negative cable to the female end of the J 38758.
IMPORTANT: The switch knob (1) on the J 38758 is marked ON and OFF. When the switch knob is in the ON position, the circuit is closed and electrical current will pass through the switch. When the switch knob is in the OFF position, the circuit is open and electrical current will not pass through the switch.
5. Turn the J 38758 knob (1) to the ON position.
6. Road test the vehicle and activate all of the accessories, including the radio and the air conditioning.
7. Turn OFF all accessories including courtesy lamps.
8. Park the vehicle. Turn the ignition switch to the OFF position and remove the ignition key.
9. Connect a 10 A fused jumper wire to the test switch tool terminals.
10. Turn the J 38758 knob (1) to the OFF position. The current flows through the jumper wire.
11. Wait one minute. If the fuse blows, use an inductive ammeter to locate the current draw.
12. Set a digital multimeter to the 10 A scale.
13. Connect the digital multimeter to the test switch tool terminals.
14. Turn the J 38758 knob (1) to the OFF position.
15. Wait one minute. Check and record the current reading.
^ When there is a current reading of 2 A or less, turn the J 38758 knob to the ON position. The electrical current will now pass through the switch.
^ Then, switch the digital multimeter to the 2 A scale for a more accurate reading.
16. Turn the J 38758 knob to the OFF position. Wait 10 minutes.
17. Check and record the current reading.
18. Note the battery reserve capacity.
^ Divide the reserve capacity by 4.
^ Compare this to the multimeter milliampere reading taken in the previous step.
^ The parasitic current drain should not exceed this number.
^ Example: If a battery has a reserve capacity of 100 minutes, the current drain should not exceed 25 mA.
Refer to Battery Usage. Battery Usage
19. Check the charging system. If the vehicle has an acceptable amount of current drain, refer to Charging System Test. Charging System Test
NOTE: 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.
20. When the vehicle has an unacceptable amount of parasitic current drain, remove each fuse one at a time until the current drain falls to an acceptable level. This will indicate which circuit is causing the drain. Refer to Power Distribution Schematics in Diagnostic Aids to diagnose exactly which part of the suspect circuit is causing the parasitic drain. In some cases a non-fused circuit or component, such as a generator, is the cause of excessive parasitic current drain.
21. Repeat the parasitic current drain test procedure after any repair has been completed to make sure that the parasitic current drain is now at an acceptable level.
22. When the cause of the excessive current draw has been located and repaired, remove the J 38758.
NOTE: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
23. Connect the battery negative cable to the battery negative terminal.
Tighten
Tighten the bolt to 15 Nm (11 lb ft).