Not consistent performance for older vehicles

Bought this product to check on my 2004 Chevy Express 3500 which is the base for a Coachmen Freedom RV. The suggested iphone\ipad apps did not show anything beyond one warning item I knew about. That was on a free app I had to install after the other apps didn't work. On my 2017 Kia Sportage, it work as expected with lots of data and feedback.

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