Battery Electrical Drain/Parasitic Load Test
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Battery Electrical Drain/Parasitic Load Test
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The following procedure is for the 12 V battery only.
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Circuit/System Description
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Components most likely to cause a parasitic draw on the vehicle"s battery are switches, relays, and control modules. After the ignition is turned OFF the control modules will begin to go to sleep (shut OFF). All control modules do not go to sleep at the same time, some may take up to 30 minutes or longer after turning the ignition off before going to sleep, like the HVAC and body control modules. Others such as the ON Star and keyless entry control modules may periodically wake up then go back to sleep. These are all normal conditions.
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Rule out any possible aftermarket equipment causing an unacceptable parasitic current drain. Aftermarket accessories installed into the courtesy lamp circuit can cause the inadvertent power timer in the body control module (BCM) to keep resetting. This would cause the BCM to remain awake and cause a current drain on the battery.
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Rule out customer driving habits such as regular short trips that do not allow enough time to properly charge the battery. Refer to
Battery Description and Operation
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A battery discharging for no apparent reason while the vehicle is parked can be caused by an intermittent draw, such as a module waking up, or a continuous draw, such as a dome light or stuck relay.
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Some systems and modules such as OnStar®, and regulated voltage control (RVC), if equipped, are designed to wake-up, perform a task, and go back asleep at regular intervals. Refer to
Body Control System Description and Operation
for the system or modules description and operation.
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An engine off natural vacuum evaporative test can occur if the engine control module (ECM) determines the drive cycle has met the appropriate criteria immediately after key off. The ECM will stay awake and the vent solenoid will stay energized for as long as 45 minutes. The typical current draw for this is about 1 A.
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Digital OnStar gen 6 and later VCIMs do not "wake up" every 10 minutes for the first 48 hours as the gen 5 and prior. Gen 6 and later VCIM current draw is very low, less than 40 mA, so the OnStar system is left in that state for up to the first 48 hours. Parasitic draw of up to 40 mA with an occasional spike as high as 80 mA through the VCIM for the first 48 hours is normal.
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Some automatic climate controls can be in a semi-activated state for up to three hours. The actual power consumption can vary depending on the vehicle platform but is typically lower than 50 mA.
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A remote central locking system has an extremely low power consumption from the receiver. The system is activated only when the car remote controls are used. When other devices on the same RKE operating frequency are activated, such as the 4 tire pressure monitoring sensors and other vehicle FOB"s in the vicinity, the RKE receiver will have a 100 mA spike. These spikes are normal and occur too briefly to have a significant effect on battery drain. Competing signals may cause RKE performance issues such as jamming but should not cause excessive battery draw.
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If an excessive current draw is not present during initial testing, continue periodic testing over a 1-2 hour period to see if the current draw increases and stays above an unacceptable level.
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Note
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The battery specification listed below is a generic specification. Refer to
Battery Usage
when testing the battery.
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The battery run down time will vary depending on the batteries reserve capacity. If the reserve capacity is higher, then the battery run down time would be longer. If the reserve capacity is lower, then the battery run down time would be shorter. The graph below indicates roughly how many days a 690 cold cranking amp battery with a 110 min. reserve capacity starting at 80 percent state of charge will last with a constant current draw until it reaches 50 percent state of charge. Differences in battery reserve capacity and temperature will affect the results.
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Current Drain
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Days
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25 mA
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33
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50 mA
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16.5
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75 mA
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11
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100 mA
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8.25
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250 mA
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3.3
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500 mA
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1.65
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750 mA
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1
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1 A
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0.8
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2 A
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0.4
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Schematic Reference
Control Module References
Connector End View Reference
Component Connector End Views
Electrical Information Reference
Scan Tool Reference
Control Module References
for scan tool information
Special Tools
EL 38758
Parasitic Draw Test Switch
For equivalent regional tools, refer to
Special Tools
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Circuit/System Verification
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Note
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Most vehicle systems will go to sleep within 30 minutes but it can take up to 2 hours before all systems power down allowing the parasitic draw test to pass. An occasional increase in the parasitic draw is normal as long as it returns within 1 second.
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Closing the door latches/ajar switch while leaving the doors open is recommended, this allows the vehicle systems to perform in a "doors closed" mode while allowing vehicle interior access that may be needed to complete the diagnostic steps.
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Locking doors will arm the vehicle content theft deterrent system if equipped. Failure to arm the system may cause a theft system fault to not be present during testing.
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There are many things that can prevent the vehicle from completely going to sleep and passing the parasitic draw test. Make sure all the conditions listed below are met before performing the parasitic current draw test.
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Key out of the ignition switch - when not equipped with keyless access and start
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Retained Accessory Power RAP OFF - open and close the driver door after ignition OFF
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Scan tool not communicating with a vehicle control module - in some cases it may need to be disconnected from the DLC
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All access doors closed
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Headlamps OFF - auto headlamps disabled
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If equipped with an under hood lamp disable it
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Any accessory that can work with ignition OFF inactive or OFF
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Wait up to 2 minutes or longer, after all other listed conditions are met
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Using an Inductive Pickup Probe
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Connect an inductive pickup probe to the negative battery cable that can read down to 1 mA.
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Ignition OFF, as the vehicle systems shut down test for less than 30 mA of parasitic current drain.
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If greater than the specified range, refer to Circuit/System Testing.
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Using the EL 38758 Parasitic Draw Test Switch
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1.
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Refer to
Battery Disconnect Warning
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Warning
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When a fused jumper wire or digital multimeter is connected to the test switch terminals, always turn the test switch ON before opening any access door, turning the ignition on, or turning any accessory on. This is to prevent damaging the jumper wire or digital multimeter fuse.
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Note
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The switch knob on the
EL 38758
switch 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.
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Ignition OFF, disconnect the battery negative cable from the battery. Refer to
Battery Negative Cable Disconnection and Connection
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Turn the
EL 38758
switch knob to the OFF position.
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Install the male end of the
EL 38758
switch to the battery ground terminal.
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Install the battery negative cable to the female end of the
EL 38758
switch.
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Turn the EL 38758
switch knob to the ON position.
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Road test the vehicle and activate all of the accessories such as the radio and air conditioning.
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Ignition OFF, connect a 10 A fused jumper wire to the test switch tool terminals.
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Turn the
EL 38758
switch knob to the OFF position. The current now flows through the jumper wire.
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Check the fuse in the jumper wire. The fuse should be OK.
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10.
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Turn the EL 38758
switch knob to the ON position. Remove the fused jumper wire.
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11.
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Connect a DMM set to the 10 A DC scale between the test switch tool terminals.
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Turn the
EL 38758
switch knob to the OFF position. The current now flows through the MM.
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As the vehicle systems shut down test for less than 30 mA of parasitic current drain.
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14.
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If greater than the specified range, refer to Circuit/System Testing.
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Note
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Removing or installing a fuse, relay, or connector, to determine the area causing high parasitic draw may wake up control modules. You must wait for the control modules to go back to sleep before retesting. It is best to install any removed or disconnected components after the diagnosis is completed.
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Fuses for power mode master components such as the BCM should be removed last to avoid misdiagnosis.
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If a scan tool is connected to the DLC, either disconnect it or subtract the scan tool current draw from the DMM reading to get the actual vehicle parasitic current draw.
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If the vehicle has an unacceptable amount of parasitic current draw, remove each fuse one at a time until the current draw falls to an acceptable level. A drop of more than 10-20 mA, when disabling a single system or circuit, is an indication of an overly high current draw that could be causing the battery drain. Refer to
Power Distribution Schematics
to diagnose exactly which circuit of the suspect system is causing the high parasitic drain. The follow is a list of common components that could cause a high current draw:
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
Control Module References
for control module replacement, programming and setup
