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1998 PCM - replaced - still not fixed?

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1998 PCM - replaced - still not fixed?

  #11  
Old 04-12-2019, 07:37 PM
zoochy
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To be clear, I'm testing the plug going into the PCM

is that 5V supply going to the PCM

or 5V from the PCM out to the transmission solenoid?
 

Last edited by zoochy; 04-12-2019 at 07:49 PM.
  #12  
Old 04-12-2019, 07:44 PM
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It isn't. That's the five volt feed for at least one sensor, if not ALL of them....... I believe that circuit has a splice, or junction somewhere, and runs off all over the place....... Which means..... One sensor that wants five volts shorting out, takes out the entire bus.
 
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Old 04-12-2019, 10:56 PM
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Yes that's a 5V supply from the PCM. It only goes to the transmission solenoid assembly but you have issues with the transmission too. One of the quirks with these PCMs is that if something shorts the sensor supply voltage anywhere it causes all sorts of different issues. I'd check sensor supplies, especially down at the transmission because quite a few people had problems with shorts inside the transmission.
 
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Old 04-13-2019, 06:16 PM
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I managed to get my truck hooked up to a scan tool today. Wasn’t convinced it would do any good but no harm in more information.

This from the mechanic:

“Attempt to communicate with scan tool but PCM will not respond, other module responding except PCM.”

So same issue as the old PCM.

I’m strategizing my trouble shooting protocol for tomorrow; lots of wires to check. Thanks for the feedback.
 
  #15  
Old 04-13-2019, 07:45 PM
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Originally Posted by zoochy View Post
I managed to get my truck hooked up to a scan tool today. Wasnít convinced it would do any good but no harm in more information.

This from the mechanic:

ďAttempt to communicate with scan tool but PCM will not respond, other module responding except PCM.Ē

So same issue as the old PCM.

Iím strategizing my trouble shooting protocol for tomorrow; lots of wires to check. Thanks for the feedback.
It is a wiring issue or bad PCM. Even if the VIN wasn't programmed, you should still be able to communicate with it.
 
  #16  
Old 04-13-2019, 08:38 PM
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That's a bizarre failure, and the odds of getting one with the exact same problem as the original is pretty much zero. You have a wiring issue. Need to follow the wires for the communication bus.
 
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Old 04-13-2019, 09:12 PM
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Originally Posted by HeyYou View Post
That's a bizarre failure, and the odds of getting one with the exact same problem as the original is pretty much zero. You have a wiring issue. Need to follow the wires for the communication bus.
I list all options because if the OP is like me the worse/rare thing that can happen will happen to me . I could be driving an all electric vehicle and still run out of gas
 
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Old 04-13-2019, 09:33 PM
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Originally Posted by MoparFanatic21 View Post
I list all options because if the OP is like me the worse/rare thing that can happen will happen to me . I could be driving an all electric vehicle and still run out of gas
Murphy's Law: Anything that can go wrong, will go wrong.

HeyYou's Law: Murphy was an optimist.
 
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Old 04-13-2019, 10:12 PM
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Originally Posted by HeyYou View Post
Murphy's Law: Anything that can go wrong, will go wrong.

HeyYou's Law: Murphy was an optimist.
I like that lol im going to use that
 
  #20  
Old 04-14-2019, 08:54 PM
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I figured it out! The Engine Speed Sensor (RPM sensor) must be shorting out internally.

I started trouble shooting by unplugging each of the 5V sensors related to the PCM and seeing if fixed the problem. When I unplug the RPM Sensor, all of the gauges work except the speedometer.

The transmission isn’t working correctly but that seems to make sense as RPM’s and the transmission talk through the PCM.

Thank you everyone for pointing me in the right direction.
 

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