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SES Light doesn't stay on - Linked to tranny issues?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by riggz, Jan 3, 2007.

  1. riggz

    riggz Registered Member

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    A few years ago my 1987 K5 w/ 700R4 tranny crapped out on me. When I had it rebuilt the shop mechanic told me the ECM wasn't functioning properly. He said it wasn't telling the tranny when to kick into OD. He also noted that the Service Engine Soon light was supposed to stay on for a few seconds after the truck was started. (It lit up when the key was turned, but once started it immediately went off.) So I replaced my ECM with one purchased from a junk yard and took it back to the shop. The mechanic said the OD was working properly and my SES light was also staying on for a few seconds after the truck started. A year later it had to be rebuilt again.

    Fast forward to the present:
    My tranny is fine until it's warmed up. After 5-10 minutes of driving it starts slipping. It makes a lot of racket when in park or neutral, then a short whine when placed into gear and the racket goes quiet. I just noticed that the SES light was no longer staying on after the truck started. So i replaced it with one from AutoZone this time (however it didn't come with the PROM chips so I had to use my old ones.) This time the SES light still isn't staying lit after starting the engine.

    Should I try and replace the chips? Is it something else that's causing the problem? I'm planning on rebuilding the tranny myself this time, but I want to fix whatever the hell is causing it to crap out on me.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Your ecm has nothing to do with how the tranny shifts, the only thing it handles is the torque converter clutch.

    Sorry you wasted so much money on the ECM's, unless you've got some other problem you aren't telling us about, I'd forget about the light not staying on for a certain period of time. It's a bulb test function, that's it. Shorting the A-B terminals on the ALDL connector should flash a code 12, that's a basic ECM test, if you get a code 12 *the ECM* thinks it's working correctly. Not that it will tell you when something is really wrong, but it's a clue.
     
  3. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    The SES light should come one when the key is in the on position with the engine off, once the engine starts it should immediately go out. The ECM has nothing to do with tranny shift points, that is controlled VIA the TV cable. The only thing that the ECM does control on the tranny is the lock up convertor solenoid.
     
    Last edited: Jan 13, 2007
  4. riggz

    riggz Registered Member

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    Hmm so what would have caused it stay on (i think maybe with the buzzer?) for a few seconds after start up?
     
  5. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    SES comes on as said with the key in the on position, blinks off, on then off when the engine starts. Sounds like your tranny guy knows as much about ecu's as he does trannys!
     
  6. riggz

    riggz Registered Member

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    Well he obviously did a horrible job with the original rebuild and so did Mr. Transmission w/ the 2nd rebuild. However he was correct when I replaced my ECU the check engine light stayed on for a couple seconds after the engine started then went out. It did this up until a couple months ago. so i dunno whats up with it.
     
  7. 6.2Blazer

    6.2Blazer 1/2 ton status

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    As mentioned the ECM has nothing to do with OD, however it does control the torque converter lockup. There is a chance that if the ECM was not telling the torque converter to lockup, this would then lead to excessive heat and a failure of the trans (the fluid would look very dark, or even black......however there could be other things causing excessive heat also).

    Also, if they did not make sure the TV cable was adjusted properly that could also cause an early failure.

    Not flushing out the cooling system, thus allowing either debris from the previous failed trans to go back into the new trans, or clogging up the cooling system could cause issues. I've also seen people re-use the torque converter, which is typically really hard to flush out (will have debris in it) which will cause a failure.
     
  8. riggz

    riggz Registered Member

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    ^^ That sounds more like what he may have been explaining and what I'm now experiencing. I've ordered the unit repair manuals and the tecnical videos DVD on how to rebuild the 700 so hopefully after educating myself a bit I can decide if it's worth it to rebuild the tranny or just buy a new one.

    Thanks for your input!
     

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