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Thread: 1998 L31 Can't turn off post cat and egr

  1. #1
    Potential Tuner
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    Jan 2021
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    1998 L31 Can't turn off post cat and egr

    My 1998 Tahoe with an L31 has the post cat O2 and EGR removed. Now I get the SES light every time It is fully warmed. About 2 miles.
    Codes are P0161 and P0401. I went into navigator and disabled P0137-141, P0157-161, and P0401-405. All of the EGR and sensor 2 DTC's.
    I also set the enable speed for the EGR test to 256MPH.
    Still getting the codes every time.

    Is it possible that my MPV12 is BS'ing me and will only do disables on P01 (0411) or later PCM's? That's my suspicion.
    Or am I not doing something IDK about? I saved all the settings, I think, before removing the HPT device.
    It's fully licensed for the truck.

    1GNEK13R6WJxxxxxx
    serial 86CCSF##72538HQY
    OS 16263425
    Black box PCM serv# 16228015
    1998 Tahoe

  2. #2
    Tuning Addict 5FDP's Avatar
    Join Date
    May 2012
    Location
    Rogers, MN
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    13,559
    It's still popping the check engine light or just appearing when you pull the codes?

    The later computers allow me to unselect the SES box, haven't looked at a black box file in a while to see if it's the same.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
    Advanced Tuner
    Join Date
    Sep 2009
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    764
    Everything needs to be set to No Error Reported and the SES box needs to be unchecked. From memory the black box is the same. I have disabled almost everything on a couple of PCMs used on non road going applications. One was a fan boat with a TPI run by a black box and the other a rock climbing buggy with a 4.3L from an Astro van.

  4. #4
    Potential Tuner
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    Jan 2021
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    Thanks, I'll give it another try.

  5. #5
    Potential Tuner
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    It's popping the SES light after about 2 miles. It's never on at startup, but comes on as soon as it warms up on the highway.