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Parasitic Battery Drains by Mike Miller

"If there is one job I never look forward to, it's a parasitic battery drain on a late model vehicles," says Mike Miller, a tech with a degree in mechanical engineering.  In this article originally published in Motor Age magazine, Mike explains how he approaches these types of jobs, it all starts with the basics.

For the most part, it will almost always be a long process to track down the cause of a parasitic battery drain in a late-model vehicle, as there are so many modules, accessories and networks involved.

The first step to diagnosing any parasitic draw starts with what’s being drawn down to begin with — the battery. I think more than any other component, the battery is the most overlooked item when it comes to testing for a parasitic drain. 

The article includes 3 case studies with different solutions:
- 2011 Dodge Challenger with a draw of nearly 2 amps with no codes. A simple TSB check lead to the cause.
- 2008 Chevrolet Tahoe with an amperage draw over 1 amp. For this one Mike used a GM Tech 2 scan tool to watch the states of the modules by using the Class 2 Message Monitor.
- 2010 GMC Yukon brought in to have a battery replaced required some measuring voltage drop across a fuse and some Ohms Law. Mike created a chart of the cold resistances from a popular fuse manufacturer and included it in this article. 

Read the complete article and grab that chart at http://www.searchautoparts.com.

Mike has a VAT40 and a Midtronics unit at his disposal for battery testing, but often he will use his PicoDiagnostics software with a PicoScope.  Setup is easy, connect channel 1 test lead to Battery Pos and Neg, on a second channel connect a high amp probe to the positive cable that connects the battery to the starter.

This PicoDiagnostics Battery test allows him to view battey voltage and current on the same screen, analyzes the data (green=good, red=bad) and quickly shows the results on screen, and "customers love the color print out," says Mike.

PicoDiagnostics software is included with the PicoScope Automotive software which can be downloaded for free and used in demo mode.

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