The Battery Electrical Drain/Parasitic Load Test diagnostic procedure found in the Engine Electrical service category in GM Service Information has been updated starting with the 2010 model year. Changes were made to enhance the diagnostic procedure and offer additional information.

More details provided by the field service engineers have been added to the Diagnostic Aids category to help technicians better understand how different components affect proper operation. For example, the diagnostic aids point out:

Aftermarket accessories installed into the courtesy lamp circuit can cause the inadvertent power timer in the BCM to keep resetting. This would cause the BCM to remain awake and cause a current drain on the battery.

An engine off natural vacuum evaporative test can occur if the 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.

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.

The Circuit/System Verification category also has been updated to use either an inductive pickup probe or the essential tool J-38758 Parasitic Draw Test Switch.

Now the technician can use either tool to perform the battery drain test. If an inductive pickup probe is available, it will greatly reduce the hook up and testing time. When using the J-38758 Parasitic Draw Test Switch, the new diagnostic procedure greatly reduces the number of steps required to determine if an excessive current draw is present or not. During testing the DMM mA current scale is no longer used, this eliminates the high risk of damaging the DMM milliamp fuse.


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