Parasitic draw problems have changed a lot over the years. Way back before when electronic control modules were used on vehicles, there was nothing to draw current from the battery once the headlights, accessories and ignition switch were switched into the off position. Now let’s take a look at today, the places on a vehicle that can cause battery drain are an endless list of things you don’t want to read.
Today’s vehicles have many electronic modules that draw current at all times, with some modules that can draw current for several hours even after the ignition switch has been turned off—Yuck! With the advancement of electronics and the seemingly endless electrical systems, parasitic draw problems are getting to be more common constantly, more and more over time. In a simpler time, using a bulb or test light to complete the ground circuit of a battery was a great way to do the testing for a parasitic draw problem.
If the bulb lit up or would glow, there was current flow; when the bulb no longer glowed, the problem was fixed. This consistently attempted (and approved!) test is no longer of value, since there is always some current flowing from the battery, powering internal “clocks” and the Keep Alive Memory (KAM) of the Engine and Transmission Control Modules (ECM and TCM). With today’s times, no tests have yet to show the correct diagnosis needed to find out exactly what the issue is and how to fix said issue.