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2000 silverado 1500 throwing emissions codes but NO check engine light

I changed the PCM and a bad alternator to no avail. The alternator was the fix for a battery light issue. The truck is running fine but if I had to get an inspection it would fail. I'm stumped.

Posted by Vincent M Donellan on

  • Carl Rock
    Carl Rock Jul 20, 2021

    Post the codes.

  • Vincent M Donellan
    Vincent M Donellan Jul 20, 2021

    PO121,125,131,133,134,135,137,140,141,151,153,154,155,157,160,161,171,172,174,175,325,327,401,404,420,430,440,442,446,461,500,502,503,560,601,603,604,605,711,724,

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2 Answers

Carl Rock

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  • Chevrolet Master
  • 3,335 Answers

You have multiple codes that could be from failed components or just from unplugging sensors and plugging back in. You need to clear the codes with a capable ODBII scan tool and note which reappear.

The engine running fine is subjective. Given the oxygen circuit faults, it's likely running a default open loop fuel strategy. So it runs ok but fuel mileage will be less than optimal.

Do you have a problem with mice where the truck is parked? The multiple circuit codes may imply rodent damage to wiring.

To fix the multiple issues is likely going to require equipment and a skill set that includes modern automotive circuit testing.

There are oxygen sensor circuit codes that could be the sensor(s) or wiring anywhere between the sensor and up to ECU/PCM and including the ECU/PCM.

If you have no experience with troubleshooting modern automotive controls I suggest you have it diagnosed by a professional.

Posted on Jul 20, 2021

  • 3 more comments 
  • Vincent M Donellan
    Vincent M Donellan Jul 20, 2021

    Carl I don't have mice in the area. I park it on the concrete driveway. I will reset the codes and let it run again. It could be I have to run it for 125 miles as others have suggested. If these options do not correct it I will have to find a good tech.

  • Vincent M Donellan
    Vincent M Donellan Jul 20, 2021

    I am now down to 14 codes. My scanner indicates I have issues with the EVAP system and the EGR system. I will drive it around for awhile tomorrow and recheck. I changed the EGR a couple of years ago so I don't suspect it. But who knows, I have seen some weird things happening with my truck.

  • Vincent M Donellan
    Vincent M Donellan Jul 21, 2021

    The 14 codes I am down to are PO141,401,440,442,446,605,1441,1810,1870,1875,U1026,1042,1192,1193. I do not have a 4wd so not sure these codes should not be thrown.

  • Carl Rock
    Carl Rock Jul 21, 2021

    I not sure I'd trust your ODBII scanner. It reports a comm error and shows faults on modules that don't exist. That implies a compatibility issue. You might try an auto parts store that reads codes just for comparison.

  • Vincent M Donellan
    Vincent M Donellan Jul 22, 2021

    Thanks for the info. I will try O'Reilly,s tomorrow as az and advanced auto only will use their scanners for check engine lights.

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john h

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  • Chevrolet Master
  • 24,403 Answers

When you disconnected the battery and pcm you cleared -erased all codes and settings [emission ready ] so you would fail inspection until vehicle went through its cycles their are quick cycles that work sometimes other is mileage usually about 125 miles for some gm vehicles --emission ready when cleared does not throw check engine light unless their is a problem or failure with one or more of the systems https://dmv.ny.gov/brochure/what-do-you-mean-my-cars-not-ready http://www.lyberty.com/car/drive-cycle.html

Posted on Jul 20, 2021

  • 1 more comment 
  • Vincent M Donellan
    Vincent M Donellan Jul 20, 2021

    I cleared the codes several times with my scanner. Does it still have to go the 125 miles?

  • john h Jul 20, 2021

    when you installed the pcm did you have it flashed for your vehicle b/c those amount of codes - is showing some kind of software problem those are not the simple emissions ready for the inspections -when ever you clear codes you have to have vehicle go through its cycle to show ready and no problems and also on your scanner should have an emission ready in it menu but you need to check the pcm for correct operation

  • Vincent M Donellan
    Vincent M Donellan Jul 20, 2021

    The PCM was flashed to my vin# before being shipped to me. My scanner does have an emissions ready in the menu but it claims all codes thrown did not pass. I have not traveled 125 miles yet. I guess I may need to burn some fuel. Road trip to Plant City, Fl. may get me 50 miles. Or Lakeland may be 75.

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