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87 K5 Trouble code 42?

Discussion in 'The Garage' started by DUKSRULE, Oct 15, 2005.

  1. DUKSRULE

    DUKSRULE 1/2 ton status

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    I have an 87 with a 5.0 I am getting trouble code 42. Truck seems to run fine but the Sev Eng light stays on. I googled it and found

    42 The EST signal did not change when the ECM applied bypass voltage to the ignition module.


    Anyone know what I need to change to get it right?
     
  2. sled_dog

    sled_dog 1 ton status

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    sounds like the module is bad. Check wiring diagram for the module and check for continuity between each of the circuits.
     
  3. DUKSRULE

    DUKSRULE 1/2 ton status

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    The ignition module in the dist?
     
  4. sled_dog

    sled_dog 1 ton status

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    yes. THat is what the code is indicating the problem to be.

    You see when you fire the truck up it runs on "Module Timing". When the PCM is ready to take over the duty of timing control it sends a voltage signal to the Ignition Module which activates a relay and Bypasses the Module. As the code is stating, the PCM is sending the signal but the Module is not being bypassed. The Relay is probably fried. Which would mean you need a new module, but test it before you just go replace it.
     
  5. DUKSRULE

    DUKSRULE 1/2 ton status

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    You are awesome. Thanks.

    I just swapped motors and left the distributor from the donor in the motor. Not sure if the module was bad or if it was because it was from a different vehicle. I took the one off the bad motor and put it in and it works like a charm and the light is out.
     
  6. sled_dog

    sled_dog 1 ton status

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    glad to help, forgot to mention the best way to test would be if you had an extra one :D
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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