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My 1994 Jeep Grand Cherokee limited was running great, as always, but then a few day ago it didn't want to idle some times and without a shudder or misfire etc. the RPM would drop down to zero and die.

I counted the check engine light flashes a few times and here they are 12,53,31,32,42,55

How did so many things go wrong all at the same time and what is wrong?

Thanks for all the help.

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The way to read the codes on your Jeep when they are flashing is, consider them blocked into two digit numbers. You'll get the first digit flashed, short pause, then the second digit. If there is more than one code, there will be a longer break, followed by the next code. Your string of codes break down into: 12. 53, 31, 32, 42, & 55. This website explains the codes:

  • 12 - Positive battery input to PCM was disconnected within the last 50 Key-on cycles.
  • 53 - PCM Internal fault condition detected.
  • 31 - An open or shorted condition detected in the A/C clutch relay circuit. Insufficient or excessive vapor flow detected during fuel evaporation emission system operation.
  • 32 - An open or shorted condition detected in the EGR solenoid circuit. Possible air/fuel ratio imbalance not detected during diagnosis. (NOTE: This code was found on this website.)
  • 42 - An open or shorted condition detected in the auto shutdown relay circuit. An open condition detected in the ASD relay output circuit. An open or shorted condition detected in the fuel pump relay control circuit. An open circuit between PCM and fuel gauge sending unit. Circuit shorted to voltage between PCM and fuel gauge sending unit. No movement of fuel level sender detected.
  • 55 - Completion of fault code display on Check Engine lamp.

The first and the last codes are very innocuous, meaning, don't worry about them (for obvious reasons).

I think the main code you need to look at is the second one (#53). It would tell me there is an issue with the PCM which is not fixable. This could be causing the rest of the remaining codes. You will want to get a second opinion, but replacement will probably be needed.

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