Battery Electrical Drain/Parasitic Load Test
12 V Battery
The following procedure is for the 12 V battery only.
Diagnostic Instructions
Circuit/System Description
Components most likely to cause a parasitic draw on the vehicles
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 min 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.
Diagnostic Aids
• |
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 may cause the BCM to remain
awake and cause a current drain on the battery. |
• |
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 . |
• |
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. |
• |
Some systems and modules such
as OnStar®, and regulated voltage control, 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. |
• |
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 min. The typical
current draw for this is about 1 A. |
• |
Digital OnStar generator 6 and
later vehicle communication interface module do not “wake
up” every 10 min for the first 48 h as the generator 5 and
prior. Generator 6 and later vehicle communication interface module
current draw is very low, less than 40 mA, so the OnStar system is
left in that state for up to the first 48 h. Parasitic draw of up
to 40 mA with an occasional spike as high as 80 mA through the
vehicle communication interface module for the first 48 h is
normal. |
• |
Some automatic climate control
systems can remain in a semi awake state for up to three hours,
actual draw amounts vary by vehicle platform but are typically not
greater than 50 mA. |
• |
An extremely low mA current
level is consumed by the remote keyless entry receiver for
monitoring purposes, actual system wake up only occurs when the
fobs for the vehicle are used. When other devices on the same
remote keyless entry operating frequency are activated, such as the
4 tire pressure monitoring sensors and other vehicle FOBs in the
vicinity, the remote keyless entry 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
remote keyless entry performance issues such as jamming but should
not cause excessive battery draw. |
• |
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. |
|
Note: The battery
specification listed below is a generic specification. Refer to the
label on the original battery when testing the battery.
|
• |
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 may be longer.
If the reserve capacity is lower, then the battery run down time
may be shorter. The graph below indicates roughly how many days a
690 cold cranking amperage 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. |
Current Drain
|
Days
|
25 mA
|
33
|
50 mA
|
16.5
|
75 mA
|
11
|
100 mA
|
8.25
|
250 mA
|
3.3
|
500 mA
|
1.65
|
750 mA
|
1
|
1 A
|
0.8
|
2 A
|
0.4
|
|
|
Reference Information
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 .
Circuit/System Verification
Note:
• |
Most vehicle
systems will go to sleep within 30 min but it can take up to 2 h
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 s. |
• |
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. |
• |
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. |
• |
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. |
|
- |
Key out of the
ignition switch – when not equipped with keyless access and
start |
|
- |
Retained
Accessory Power OFF – open and close the driver door after
ignition OFF |
|
- |
Scan tool not
communicating with a vehicle control module – in some cases
it may need to be disconnected from the DLC |
|
- |
All access doors
closed |
|
- |
Headlamps OFF
– auto headlamps disabled |
|
- |
If equipped with
an under hood lamp disable it |
|
- |
Any accessory
that can work with ignition OFF inactive or OFF |
|
- |
Wait up to 2 min
or longer, after all other listed conditions are met |
Using an Inductive Pickup Probe
1. |
Connect an inductive pickup
probe to the negative battery cable that can read down to 1
mA. |
2. |
Ignition OFF, as the vehicle
systems shut down test for less than 30 mA of parasitic current
drain. |
⇒ |
If greater than the specified range, refer to
Circuit/System Testing. |
Using the EL 38758 Parasitic Draw Test Switch
|
Caution: 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. |
|
Note: 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.
|
2. |
Turn the EL 38758
switch knob to the OFF position. |
3. |
Install the male end of the
EL 38758 switch to the battery ground
terminal. |
4. |
Install the battery negative
cable to the female end of the EL 38758 switch
. |
5. |
Turn the EL 38758
switch knob to the ON position. |
6. |
Road test the vehicle and
activate all of the accessories such as the radio and air
conditioning. |
7. |
Ignition OFF, connect a 10 A
fused jumper wire to the test switch tool terminals. |
8. |
Turn the EL 38758
switch knob to the OFF position. The current now flows
through the jumper wire. |
9. |
Check the fuse in the jumper
wire. The fuse should be OK. |
⇒ Failed: If the jumper wire fuse
is blown, refer to Circuit/System Testing.
⇓ Passed
10. |
Turn the EL 38758
switch knob to the ON position. Remove the fused jumper
wire. |
11. |
Connect a DMM set to the 10 A
DC scale between the test switch tool terminals. |
12. |
Turn the EL 38758
switch knob to the OFF position. The current now flows
through the DMM. |
13. |
As the vehicle systems shut
down test for less than 30 mA of parasitic current drain.
|
⇒ |
If greater than the specified range, refer to
Circuit/System Testing. |
Circuit/System Testing
Note:
• |
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. |
• |
Fuses for power
mode master components such as the BCM should be removed last to
avoid misdiagnosis. |
• |
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. |
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
following is a list of common components that could cause a high
current draw:
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic
procedure.
Control Module References for control module replacement,
programming and setup
|