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  1. P

    Cat 272d2 XHP preheat issue

    negative. customer did not care that the preheat was not working. asked to price out part for future reference and took the machine back as is. I never had the chance to cut the harness apart to look for a short.
  2. P

    Cat 272d2 XHP preheat issue

    When i was diagnosing the short that is how i found where it was. Between conn22 and conn-rpc9 the wire f793 was shorted to ground. My theory is that wire shorted and there is no fail safe (fuse) between that and the ecm. So the short ended up damaging the ecm internally. Kind of silly the...
  3. P

    Cat 272d2 XHP preheat issue

    If i apply 12v directly to the relay via rpc9 the relay clicks and sends 12v directly to the intake heater. With a 20k ohm resistor in line of the temp sensor et reads -15*. Et shows start aid relay “on”. There is no voltage to start aid relay signal.
  4. P

    Cat 272d2 XHP preheat issue

    Yeah. It looks just like a starter solenoid. But cat i believe refers to it as a relay. Pin 24. Ecm connector 2 Intake heater relay coil +.
  5. P

    Cat 272d2 XHP preheat issue

    I am getting both -3 and -4. I have the schematic. I pinned it directly from the ecm plug and with the plug to the solenoid unplugged have 9.3v. With the plug plugged in 0v.
  6. P

    Cat 272d2 XHP preheat issue

    Correct power supply to signal side of solenoid was shorted to ground. Sn-dx200402
  7. P

    Cat 272d2 XHP preheat issue

    what did you end up finding with this? I have a 299 doing the same thing. Found a dead short on the signal for the solenoid. Fixed that but now only getting 9.3v out of the ecm to the signal side of the coil.
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