Battery (Parasitic) Load Test
PARASITIC LOAD TESTIf the battery discharges while the vehicle sits for a few hours or days, the vehicle should be diagnosed for parasitic loads. Simple connection of an ammeter in series with the battery may not find the cause as the condition may not show up when power is restored unless that particular component is repeatedly cycled. Parasitic loads can be diagnosed using either one of the following procedures but use of essential tool J 38758 is recommended.
J 38758 Parasitic Draw Test Switch:
Parasitic Draw Test:
TOOLS NEEDED
^ J 38758 Parasitic Draw Test Switch.
^ Ammeter with at 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 the engine running or damage could occur to the attached ammeter or the vehicle electrical system.
1. Check for diagnostic codes and perform diagnosis for codes set.
2. Turn test switch knob to the "OFF" position.
3. Remove battery cable from battery negative terminal.
4. Install parasitic draw test switch male (cable) end to negative battery terminal.
5. Install negative battery cable to female end of the test switch tool.
6. Turn the test switch tool knob to the "ON" position.
7. Road test vehicle while activating all accessories (radio, A/C, etc.).
8. Turn ignition switch to the "Locked" position and remove ignition key
9. Set ammeter to the 10 amp scale and connect to terminals on test switch tool with alligator clips. Use of the 10 amp scale may prevent damage to meter.
10. Turn test switch tool knob to the "OFF" position to allow current to flow through the ammeter.
Component Parasitic Loads:
11. Check current reading. Allow 30 seconds for reading to stabilize. Verify that Retained Accessory Power (RAP) is off. Electronic Level Control (ELC) may remain active for up to 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 25 milliamps, (0.025A) refer to Component Load chart for specific current loads for a microprocessor that may be in the "awake" state. A current reading below 25 milliamps is normal. A reading of (0.OA) indicates an open circuit with the meter connection or test switch.
Component Parasitic Loads:
12. If current draw is more than 25 mA and does not correspond to a value in Figure, the circuit causing the excessive draw must be isolated. While monitoring the ammeter, remove fuses and breakers one at a time in the following order: 1st) Mini fuses; 2nd) Circuit breakers; 3rd) Maxi fuses, until the current reading is 25 mA or less. Once the fuse or circuit breaker associated with the excess draw is determined refer to electrical diagnosis for specific circuit schematics. Excess draws may be caused by shorts to ground, sticking relays, or low power lamps remaining lit.
13. If excess current draw is present with all fuses and breakers removed, the positive battery cable circuit may be the cause.
DIAGNOSING THE BATTERY CABLE CIRCUIT
^ Remove battery circuit from the generator output stud. If draw is gone refer to generator diagnosis.
^ Remove the battery circuit from underhood power distribution center. If draw is gone, repair short to ground at relay and fuse blocks.
^ Remove battery circuit from starter solenoid on 4.9L or at battery on 4.6L. If draw is gone refer to starter motor diagnosis.
^ If draw is present with battery circuits disconnected, the positive battery cable is shorted to ground. Locate and repair short to ground or replace cable as necessary.
14. Turn the test tool to "OFF", remove the tool and reconnect the negative battery cable to the negative battery terminal.
15. If no excessive current draw is found, the charging system should be checked.
ALTERNATE PARASITIC LOAD TEST
Component Loads:
Alternate Parasitic Load Diagnosis Procedure:
^ 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 a battery side terminal adapter, AC-Delco ST-1201 or equivalent, in the negative terminal of the battery.
3. 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. With all lights, accessories, Retained Accessory Power (RAP), 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 or 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 time for the initial draw to occur or check for reduced current with an inductive ammeter (current clamp) and proceed to Step 5,
5. If the current reading is 2.0 amps or less, connect the digital multi-meter, set on the 2000 mA DC range, in parallel with the high capacity ammeter.
6. Disconnect the high capacity ammeter or battery cable section and take the reading with the digital multi-meter.
7. If current draw is more than 30 mA and does not correspond to a value in Figure, the circuit causing the excessive draw must be isolated. While monitoring the ammeter, remove fuses and breakers one at a time in the following order: 1st) Mini fuses; 2nd) Circuit breakers; 3rd) Maxi fuses, until the current reading is 30 mA or less. Once the fuse or circuit breaker associated with the excess draw is determined refer, to electrical diagnosis for specific circuit schematics. Excess draws may be caused by shorts to ground, sticking relays, or low power lamps remaining lit.
8. If excess current draw is present with all fuses and breakers removed, the. positive battery cable circuit may be the cause.
DIAGNOSING THE BATTERY CABLE CIRCUIT
^ Remove battery circuit from the generator output stud. If draw is gone refer to generator diagnosis.
^ Remove the battery circuit from underhood power distribution center. If draw is gone, repair short to ground at relay and fuse blocks.
^ Remove battery circuit from starter solenoid on 4.9L or at battery on 4.6L. If draw is gone refer to starter motor diagnosis.
^ If draw is present with battery circuits disconnected, the positive battery cable is shorted to ground. Locate and repair short to ground or replace cable as necessary.
9. Reconnect battery negative cable.
10. If no excessive current draw is found, 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 may not be able to recharge the battery between starts.
If this situation is suspected, the driver should be instructed in ways to reduce battery drain. Limiting the use of the rear window defogger, heated windshield and setting the Twilight Sentinel on the minimal delay, etc, are helpful in this regard.