Component Tests and General Diagnostics
PARASITIC LOAD TEST USING J 38758J 38758 Parasitic Draw Test Switch:
Parasitic Draw Test:
TOOLS REQUIRED:
^ J 38758 Parasitic Draw Test Switch
^ Ammeter with a least 10 amp DC current capacity and milliamp measurement capability
NOTICE: The parasitic draw test switch should never be turned to the "OFF" position with engine running or damage could occur to the attached ammeter or the vehicle electrical system.
1. Turn test switch knob to the "OFF" position.
2. Remove battery cable from battery negative terminal.
3. Install parasitic draw test switch male (cable) end to negative battery terminal.
4. Install negative battery cable to female end of the test switch tool.
5. Turn the test switch tool knob to the "ON" position.
6. Road test vehicle while activating all accessories (radio, A/C, etc.).
7. Turn ignition switch to the "LOCKED" position and remove ignition key.
8. Set ammeter to the 10 amp scale and connect to terminal on test switch tool with alligator clips. Use of the 10 amp scale may prevent damage to meter.
9. Turn test switch tool knob to the "OFF" position to allow current to flow through the ammeter.
10. Check current reading. Allow time for reading to stabilize. Verify that retained accessory power (RAP) is off. Electronic level control (ELC) may remain active for up to 6 minutes and Central Control Module (CCM) will remain active for 10 minutes. If current reading is at or below two amps. Turn the test tool knob to the "ON" position (to maintain continuity in the electrical system) and switch to a lower scale for a more accurate reading, or install a more accurate meter, if necessary. Turn test tool knob to "OFF." If current reading is above 40 milliamps, refer to Component Parasitic Load chart for specific current loads and microprocessor "time-outs." Total reading below 20 milliamps is normal.
11. If current draw is above specifications listed in the Component Parasitic Load chart, remove system fuses and circuit breakers one a a time until the current draw returns to a value less than or equal to the specifications listed. This should be done while monitoring the ammeter so that a disruption of the drain will be evident. Perform Steps 9 and 10 each time a fuse is removed. Total readings in the hundreds of milliamps may suggest grounded wires, sticking relays, or small lamps remaining lit.
IMPORTANT
^ Always turn the test switch tool knob to the "ON" position before removing each fuse to maintain continuity in the electrical system and to avoid damaging the ammeter due to accidental overloading (i.e., opening door). Do not turn switch to "OFF" while the engine is running.
12. When excessive current draw cause has beer located and repaired. repeat steps 9 and 10 to verify the repair. Then turn the test tool to "OFF," remove the tool, and reconnect the negative battery cable to the negative battery terminal.
^ Before performing a follow up test drive, allow HVAC to calibrate itself due to disconnecting battery assembly.
ALTERNATE PARASITIC LOAD TEST
Alternate Parasitic Load Diagnosis Procedure:
Component Parasitic Loads:
^ The following alternate procedure may be used when testing for parasitic loads if J 38758 is not available:
1. Disconnect Battery Negative Cable
2. Install Side Terminal Adapter install a battery side terminal adapter AC-Delco ST-1201 or equivalent, in the negative terminal of the battery.
3. Install Nut to Cable. Install the other ST-1201 or a 3/8" nut with standard threads (16 UNC) on the negative battery cable attaching screw to assure a good electrical contact with the metal face on the cable for testing (add a washer behind the nut if the nut does not contact firmly). Yellow or black finish nuts are generally non-conductive and should not be used.
4. Install High Capacity Ammeter. With all lights, accessories and the ignition switch 'OFF", connect a high capacity ammeter (at least 10 amps) from the negative battery cable to the side terminal adapter. This high capacity ammeter is connected to verify whether of not a high current draw is occurring at a constant rate. It is this type of high current draw which will blow the fuse in lower capacity ammeters.
NOTICE: If a high capacity ammeter is not available, install a section of heavy wire (preferably battery cable section) between the existing battery negative cable and the side terminal adapter. Allow ample time (approximately 30-60 seconds) for the initial draw to occur or check for reduced current with an inductive ammeter (current clamp) and proceed to Step 5.
5. Install DVM With the high capacity ammeter or battery cable section still connected, connect the digital multi-meter, set on the 2000 DCmA range, in parallel with the high reading ammeter.
6. Disconnect High Capacity Ammeter Disconnect the high capacity ammeter and take the reading with the digital multi-meter. A current draw of 50 mA or less (25mA is normal) indicates that all lights and accessories are off and that there is no unexplained current draw. Care should be taken to allow for a time delay before reading the meter because of the electronic level control feature.
Component Parasitic Loads:
7. Determining the Source of the Draw. Once is has been determined that a parasitic drain in excess of 50 mA exists, a visual inspection for the vehicle should be performed. Check to see if there are any unwanted lights on, motors running or switches/relays activating. If no cause for the draw is immediately apparent, it may be possible to narrow in on the source by systematically removing fuses and circuit breakers, -one by one, from the fuse panels. This should be done while monitoring the ammeter so that a disruption on the drain will be evident. Refer to figure for average and maximum parasitic loads for various components.
CHECK CHARGING SYSTEM
If a battery becomes discharged and no excessive current drain is found, the operation of the charging system should be checked.
DRIVER RELATED CONDITION
If no cause is found for a discharged battery and the battery tests good, a light may have been left on, or the driving habits of the owner may be such that, especially with many short trips and repeated starts, the generator does not get a chance to recharge the battery between starts.
If this situation is suspected, the driver should be instructed on ways to reduce battery drain. Limiting the use of the rear window defogger and setting the twilight sentinel on the minimum delay, etc. are helpful in this regards.