Hummer H2. Manual - part 1122

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 checked for an excessive electrical drain. This is referred to as Parasitic Current 
Drain. 

If a battery needs recharging and no cause is evident, check the vehicle for excessive parasitic current drain. 

One or more on-board solid state control modules, such as the body control module (BCM) 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 an ammeter, etc., the excessive current drain may not occur once the circuit continuity is 
restored. Even though cycling the ignition key to the RUN and then to the OFF position may 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, ensure that the ignition switch is in the LOCK position, all electrical accessories 
are turned OFF, the underhood lamp is disconnected, the door glass is open and the doors are closed. 

1. Disconnect the battery negative cable. Refer to Battery Negative Cable Disconnect/Connect Procedure 

(Single Battery) . 

CAUTION: Refer to Battery Disconnect Caution in Cautions and Notices.

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.

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.

 

2004 Hummer H2 

2004 ELECTRICAL Engine Electrical - Hummer H2

  

Fig. 5: Connecting J 39200 & J 38758 To Battery Cable 
Courtesy of GENERAL MOTORS CORP. 

2. Install the male end of the J 38758 Parasitic Draw Test Switch to the battery negative terminal. See 

Special Tools and Equipment .  

3. Turn OFF the test switch.  

4. Install the battery negative cable to the female end of the test switch.  

5. Turn ON the test switch.  

6. Road test the vehicle while activating all accessories, including the radio and the air conditioning.  

7. Turn OFF the ignition switch. Remove the key. 

IMPORTANT: From this point on, electrical continuity must be maintained in the ground 

circuit of the battery through the J 38758 in the ON position or through 
theJ 39200 . The BCM can draw several amps of current after the ignition 

 

2004 Hummer H2 

2004 ELECTRICAL Engine Electrical - Hummer H2

  

8. Install the scan tool and perform the power down now feature from the BCM output menu. After 

performing this function the scan tool can be powered off or disconnected, then wait an additional 5 
minutes before continue testing.  

9. Set the J 39200 Digital Multimeter to the 10 A scale. 

1. Connect a jumper wire with an in-line 10 A fuse J 36169-A to the terminals of the test switch.  

2. Turn the test switch to the OFF position.  

3. Wait 10 seconds.  

4. If the fuse does not blow, the current is less than 10 A and the ammeter can be used safely.  

5. Turn the test switch to the ON position before the fused jumper wire is removed and the multimeter 

is installed.  

10. Connect the ammeter to the test switch terminals.  

11. Turn OFF the test switch. This allows the current to flow through the ammeter.  

12. Wait at least 60 seconds, then check the current reading. 

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When there is a current reading of 2 A or less, turn ON the test switch, this maintains continuity in 
the electrical system.  

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Then, switch the meter down to the 2 A scale, for a more accurate reading, when the test switch is 
reopened.  

13. Take the reading in milli-amps.  

14. Note the battery reserve capacity. Refer to Battery Usage . 

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Divide this number by 4.  

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Compare this to the multimeter reading.  

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The current drain should not exceed this number.  

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Example: If a battery has a reserve capacity of 100 minutes, the current drain should not exceed 25 
milli-amps. If the vehicle has 2 batteries, add the reserve capacities together and divide this total by 
4.  

15. When the current draw is too high, remove the electrical system fuses one at a time until the draw returns 

to a value less than or equal to specifications. 

is turned off. Refer to Body Control System Description and Operation in 
Body Control System. See Special Tools and Equipment .

IMPORTANT: If an ammeter other than the J 39200 is used, ensure that the vehicle does 

not have a high current drain that would damage the ammeter when 
connected to the circuit. This can be done using the following procedure:

NOTE:

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.

 

2004 Hummer H2 

2004 ELECTRICAL Engine Electrical - Hummer H2

  

16. Repeat the parasitic current drain test procedure after any repair has been completed.  

17. When the cause of the excessive current draw has been located and repaired, remove the meter and the 

parasitic draw test switch and terminal adapters.  

18. Connect the negative cable to the battery negative terminal. Refer to Battery Negative Cable 

Disconnect/Connect Procedure (Single Battery) .  

BATTERY COMMON CAUSES OF FAILURE 

A battery is not designed to last forever. With proper care, however, the battery will provide years of good 
service. If the battery tests good but still fails to perform well, the following are some of the more common 
causes: 

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A vehicle accessory was left on overnight.  

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The driving speeds have been slow with frequent stops with many electrical accessories in use, 
particularly air conditioning, headlights, wipers, heated rear window, cellular telephone, etc.  

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The electrical load has exceeded the generator output, particularly with the addition of aftermarket 
equipment.  

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Existing conditions in the charging system, including the following possibilities: 

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A slipping belt  

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A bad generator  

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The battery has not been properly maintained, including a loose battery hold down or missing battery 
insulator if used.  

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There are mechanical conditions in the electrical system, such as a short or a pinched wire, attributing to 
power failure. Refer to General Electrical Diagnosis Procedures in Wiring Systems.  

Electrolyte Freezing 

The freezing point of electrolyte depends on its specific gravity. A fully charged battery will not freeze until the 
ambient temperature gets below -54° C (-65° F). However, a battery with a low state of charge may freeze at 
temperatures as high as -7° C (+20° F). Since freezing may ruin a battery, the battery should be protected 
against freezing by keeping it properly charged. As long as the green eye is visible in the hydrometer, the 
freezing point of the battery will be somewhere below -32° C (-25° F). 

Battery Protection During Vehicle Storage 

Certain devices on the vehicle maintain a small continuous current drain on the battery. A battery that is not 
used for an extended period of time will discharge. Eventually permanent damage will result. Discharged 
batteries will also freeze in cold weather. Refer to Battery Inspection/Test (Non-HP2) . 

In order to maintain a battery state of charge while storing the vehicle for more than 30 days: 

IMPORTANT: If a green dot is not visible in the hydrometer, charge the battery. Refer to 

Battery Charging .

 

2004 Hummer H2 

2004 ELECTRICAL Engine Electrical - Hummer H2