I Reset the computer in my 1998 Chevy Astro, but even after driving around for a few days and putting it through the GM drive cycle, the OBDII reader is saying that the CAT monitor is not ready. I suspect there is a sensor somewhere that is sending incorrect information to the computer. Is there any way to diagnose this? Or at least a list of the precise conditions that need to be present in order for the CAT test to be completed? Thanks!

2 Answers 2


Refer to this page for what the PCM is looking for in a full OBDII drive cycle: http://www.obdii.com/drivecycle.html


May require (on some vehicles, I'm not familiar with GM specifically) 15 minutes of steady cruise on the expressway to get all monitors to readiness.

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