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Old 11-05-2017, 12:49 AM   #12
BR3W CITY
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Join Date: Sep 2009
Location: MKE WI
Posts: 6,987
Re: What Code Reader/Scanner to Buy?

I/M is usually in reference to I/M readiness monitors. They are ECM set "flags" of activity that exist to monitor cycling of certain systems. If you were to watch it on a monitor like HPT ECM Scanner, you'd see they have counts that track certain things like start cycles, mileage etc.

When you scan and clear codes, it sets the cleared systems to 0. For things like emissions systems, its usually around a 200mile cycle. This is so you can't spoof the system by rapidly force-clearing codes. Its basically a bull**** detector. The most common way to observe this is with the gas cap emissions code (evap). If you loosen the cap and start the truck, it may see the pressure drop and trigger the code. You can then go tighten the cap and drive a little bit...and once a requisite mileage amount or start cycle count is reached, the code will clear itself because its observed the "failure" as no longer there.
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