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Support Forum » OBD II Ground Question

February 14, 2011
by zachrattner
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I recently purchased a NerdKit to build the OBD II project posted on your website ( I found an OBD II pinout diagram online (, and I'm a little confused by the difference between pins 4 and 5. Pin 4 is a chassis ground, and pin 5 is a signal ground. Is it safe to connect both of these lines to the negative bus on a breadboard? If so, then why are they two separate pins?

Thanks, Zach

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