Diagnostic errors, "catalyst" and "EVAP" as "not ready"

Tiny
KODIAK4
  • MEMBER
  • 2003 GMC SONOMA
  • 4.3L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 136,000 MILES
When I took the truck for annual emissions/safety inspection, the state emission computer showed my "catalyst" and "Evap" as "not ready". Although I don't have a check engine warning light on, I went to the local auto parts and had them check it, it didn't throw any codes but said (again) the catalyst and evaporative systems weren't "reporting". The truck is running great, and I'm wondering if a previous owner might have "unplugged" something that has caused these systems to not be able to communicate with the main computer, and why don't I have a check engine light blaring at me?

I've driven a couple hundred miles over a couple weeks since the battery has been unattached.
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Sunday, May 15th, 2022 AT 9:23 AM

3 Replies

Tiny
KEN L
  • ADMIN
This sounds like you have a broken thermostat which allows the engine to warm up too slow, this will not allow the computer to go into "closed loop" within a specific amount of time. This is why there are no codes because the computer is not set up for this kind of failure. There is a guide to walk you through the replacement and inspection with instructions below to show you how on your car.

https://www.2carpros.com/articles/replace-thermostat

Check out the diagrams (below). Let us know what happens and please upload pictures or videos of the problem.
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Monday, May 16th, 2022 AT 9:46 AM
Tiny
KODIAK4
  • MEMBER
I'll be replacing the thermostat today and will let you know if it resolved the problem. Thanks for the information, I would have never thought about this as a possible cause.
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Wednesday, May 18th, 2022 AT 8:43 AM
Tiny
KEN L
  • ADMIN
Yes, the computer needs to go through its cycle. Please let me know what the thermostat looks like, it should be obvious.
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Wednesday, May 18th, 2022 AT 11:32 AM

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