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Unread 10-24-2011, 06:29 PM   #1
paulme
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Voodoo fixes p0505 code on 96 Cherokee Sport

Brand new to this forum, first-time Jeep owner.

Got tired of oil leaks so I replaced oil pan gasket at 185k mi over 3 days (various other issues encountered and dealt with). The whole time I had the battery disconnected. No connectors disconnected or electrical anything messed with. After fixes, car refuses to run. Pull code P0505 re: Idle Air Control system. OK. System refuses to idle so this makes sense. Consult various jeep fora for advice about P0505. One obscure posts suggest the following: 1) disconnect battery,
2) touch negative terminal to positive battery post, 3) wait for a few seconds, 4) reconnect battery, 5) start car with problem mysteriously gone.

After trying everything else, but before swapping out IAC motor, I performed the above mystic incantation and, sure enough, the problem is resolved and the car now runs normally. Anyone care to comment?

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Unread 10-24-2011, 07:33 PM   #2
CJ7-Tim
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You performed an engine computer re-boot and deleted the corrupted engine idle data.
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Unread 10-25-2011, 06:01 AM   #3
unkajeffy
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Tim.............You Rock!!
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Unread 10-25-2011, 07:18 AM   #4
paulme
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Engine Computer Data Corruption

Quote:
Originally Posted by CJ7-Tim View Post
You performed an engine computer re-boot and deleted the corrupted engine idle data. When you can fix it by threating it with a large hammer you will be a voodoo master Jedi.
Thanks, Tim. It is clear that when either 1) the battery goes dead for several days or 2) the battery is simply disconnected for several days, that PCM data corruption is a likely result. Why isn't the PCM reset process I described discusses more broadly on these fora?

Is there a discussion anywhere of how the PCM gathers its data regarding various closed-loop control processes and how this data might become corrupted and thus need to be reset?
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Unread 10-25-2011, 08:12 AM   #5
CJ7-Tim
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For 1996+ OBD-II, sometimes the ECU data can be faulty due to a failed sensor or it can get corrupted by low voltage.

This very simple procedure will Erase the “Adaptive Memory” stored inside the PCM and allow a new “Adaptive Memory” to be developed. After performing this procedure the PCM will re-learn and store into Adaptive Memory your engines performance characteristics.
Please perform these steps exactly as they are written, in the order they are written. This will cause the adaptive memory in the PCM to be erased and cause the PCM to go into Fast Learn Mode adaptive mode.

Disconnect the POSITIVE battery Terminal and touch it to ground ( not the battery negative terminal ) for 30 seconds. The engine block or the A/C compressor pump will work as a ground. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory).

Reconnect the Battery Cable
Turn Ignition Switch to the “On” position but DO NOT start the engine
Turn Headlight “On”
Turn Headlights “Off”
Turn Ignition Key “Off”


The PCM Adaptive memory has now been flashed, or erased from the PCM. When you start the engine it will now be running off a set of pre-programmed tables that come with the PCM from the factory. When you get the engine up to operating temperature the PCM will start to collect data for the “Adaptive Memory”. The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.
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Unread 10-26-2011, 02:09 AM   #6
paulme
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re: clearing adaptive memory

Thank you very much. That clears it up. I didn't follow the procedure, and, in fact did something quite different, but it apparently had the same effect. It would be useful to post in a FAQ somewhere just which codes might be erroneously produced by data corruption in the PCM and thus the PCM ought to be "flashed" before trying to run ephemerally generated codes to the ground if there is any suspicion of data corruption.
Just my 2 cents.

Thanks again for your help.
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Unread 10-26-2011, 02:41 AM   #7
CJ7-Tim
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What you did sometimes has the same effect, sometimes not. What it usually does is just delete any stored OBD-II Check Engine Light trouble codes.
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Unread 02-16-2013, 09:53 AM   #8
swt2c
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Thanks TIm - this worked for me as well (97 XJ on which I had just replaced the starter) to clear a P0505.
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