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Unread 11-22-2009, 11:24 AM   #1
shahriarrrr
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Code P0505, IAC or changing the whole PCM?

I got "Check engine light", checked, P0505, IAC valve issues, changed it, still " check engine" on with the same code, took to the dealer, recommeded to change the whole PCM!!! any idea/ recommendation?

BTW, car runs and starts fine, no problem, just the light

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Last edited by shahriarrrr; 11-22-2009 at 11:28 AM.. Reason: spelling issues
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Unread 11-22-2009, 11:39 AM   #2
JrMechanic
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Did you reset the light after you fixed it? Either get a OBDII scanner and erase the code, or pull the positive battery terminal for a few seconds.
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Unread 11-22-2009, 01:06 PM   #3
baxy
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well I hope the deal checked the wiring there are 4 wires that can be responsible for setting that DTC
any one which can have a short to ground or voltage or open
it only has to happen intermittantly for 100 milliseconds to pick up as a code
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Unread 11-22-2009, 01:20 PM   #4
shahriarrrr
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I already erased it couple of times, comes back
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Unread 11-22-2009, 01:21 PM   #5
shahriarrrr
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how should I check for the short on those 4 wires?
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Unread 11-22-2009, 01:34 PM   #6
shahriarrrr
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Originally Posted by baxy View Post
well I hope the deal checked the wiring there are 4 wires that can be responsible for setting that DTC
any one which can have a short to ground or voltage or open
it only has to happen intermittantly for 100 milliseconds to pick up as a code
How should I check for short circuit on those 4 wires?
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Unread 11-22-2009, 02:27 PM   #7
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multimeter
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Unread 11-22-2009, 04:02 PM   #8
rm2001wj
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In operation with the engine idling normally, two of the wires will have 12 V on them and the other two will be grounded. If you knew which two are supposed to have the 12 V with the engine running, then you could use an ohmmeter (or the ohmmeter function of a multimeter) to check the resistance when the engine is not running. Zero or near zero resistance would indicate a short. However, who knows which two of the four wires need to be checked?

You would normally expect that the two "ground wires" would be shorted, but because the PCM usually turns on a circuit by providing the connection to ground, that won't necessarily be the case with the engine off. So, even if you knew which of the two wires would be grounded with the engine running, those two would not necessarily show zero resistance with respect to ground when the engine is off. Neither a zero resistance (a shorted condition) between either of those two wires and ground nor an infinite resistance (open condition) can much give useful info unless you know more details of how the PCM operates the IAC motor.

About the best you can do is measure the voltage relative to a good ground of each of the 4 wires with the engine running. If any two wires show 12 V and the other two show zero volts, then the IAC circuits are probably ok. Failing to get these results, means the wiring connector or wiring harness or PCM or even the IAC motor could be the problem.

If you understand what I have said and make the recommended voltage measurements, please post the results.
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Unread 11-22-2009, 04:29 PM   #9
shahriarrrr
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Quote:
Originally Posted by rm2001wj View Post
In operation with the engine idling normally, two of the wires will have 12 V on them and the other two will be grounded. If you knew which two are supposed to have the 12 V with the engine running, then you could use an ohmmeter (or the ohmmeter function of a multimeter) to check the resistance when the engine is not running. Zero or near zero resistance would indicate a short. However, who knows which two of the four wires need to be checked?

You would normally expect that the two "ground wires" would be shorted, but because the PCM usually turns on a circuit by providing the connection to ground, that won't necessarily be the case with the engine off. So, even if you knew which of the two wires would be grounded with the engine running, those two would not necessarily show zero resistance with respect to ground when the engine is off. Neither a zero resistance (a shorted condition) between either of those two wires and ground nor an infinite resistance (open condition) can much give useful info unless you know more details of how the PCM operates the IAC motor.

About the best you can do is measure the voltage relative to a good ground of each of the 4 wires with the engine running. If any two wires show 12 V and the other two show zero volts, then the IAC circuits are probably ok. Failing to get these results, means the wiring connector or wiring harness or PCM or even the IAC motor could be the problem.

If you understand what I have said and make the recommended voltage measurements, please post the results.
I'm still confused but I'll give it a try aand will keep you posted of the results.
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Unread 11-22-2009, 08:25 PM   #10
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or you could unplug the computer and the IAC measure the resistance of each wire from the PCM connector to IAC connector for resistance should be less than 2 or 3 ohms then measure each wire for resistance to ground with both connectors unplugged should be open line then check each wire for short to voltage

you really do need the test out of the FSM for this code to follow
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Unread 02-11-2011, 05:34 PM   #11
Loki139
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Quote:
Originally Posted by shahriarrrr View Post
I got "Check engine light", checked, P0505, IAC valve issues, changed it, still " check engine" on with the same code, took to the dealer, recommeded to change the whole PCM!!! any idea/ recommendation?

BTW, car runs and starts fine, no problem, just the light
Sounds like I have the exact same problem. Did you ever resolve the code problem??
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Unread 06-27-2011, 12:48 PM   #12
ripdawwg
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Bump

Did you ever figgure this out I have the EXACT same issue and it is driving me batsh###t
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Unread 06-28-2011, 08:51 AM   #13
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I know the feeling. My problem was the PCM. Took it to the dealer, they replaced the IAC, and checked the wires for any shorts, then reprogramed my computer and everything was okay. I took it home and just an hour later the idle would dip slightly and then set off the code. I took it back and the only thing left to do was replace the PCM. That fixed it. $500 and 3 months later there is no problem. Good luck!
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Unread 11-09-2011, 04:01 PM   #14
el_duonger
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PCM Replacement

Quote:
Originally Posted by Loki139 View Post
I know the feeling. My problem was the PCM. Took it to the dealer, they replaced the IAC, and checked the wires for any shorts, then reprogramed my computer and everything was okay. I took it home and just an hour later the idle would dip slightly and then set off the code. I took it back and the only thing left to do was replace the PCM. That fixed it. $500 and 3 months later there is no problem. Good luck!
How's the car running now? $500 is a good deal on the part. The mopar PCM retails for $682 with a $125 core charge on top, and then there's labor. I'm looking at $700 through an independent who can program the PCM. Not a cheap fix.
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Unread 11-09-2011, 04:50 PM   #15
el_duonger
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Aftermarket Rebuilt PCM (Powertrain Control Modules) Experience???

Anybody have experience with aftermarket PCMs? Where they take your PCM part number, your VIN, mileage, year, make, model, emission state and program the PCM for you.

My mechanic will install and scan to ensure it's operating properly but can't program. Only dealerships can in my area. Would rather work with my mechanic who does great work at reasonable prices.

I'm finding that the rebuilt PCMs run about $200+ with overnight shipping and lifetime warranties (with return of core). Anybody done this before with their JGCs/WJs? The vendors I'm finding don't have many reviews and have sold a bunch on eBay. Names include "All Computer Resources", "ECM Depot", "Auto Computer Exchange" and "Solo Auto Electronics" (www.solopcms.com). Oddly enough most of these companies are located in FL. Not sure that has anything to do with hurricane Katrina and the large # of Jeeps whose PCMs got trashed from flooding.

So I'm looking at $700 total for a direct from Mopar PCM, programmed by a dealership and installed. Or about $400 for an aftermarket pre-programmed PCM and installed by my mechanic. Hate spending more $$ than necessary but want to be sure I'm not screwing myself.

Thanks for any info any fellow Jeep peeps can provide.
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