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Robert R
Robert R, ASE Certified Technician
Category: Chrysler
Satisfied Customers: 3890
Experience:  28 years experience, ASE Master Certified, Chrysler Master Certified, Sprinter Van Certified
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1999 Dodge Durango has a check engine light and code P0505.

Customer Question

1999 Dodge Durango has a check engine light and code P0505. I changed the IAC for a new one and the code still comes back immediately. I then checked the wiring for shorts and grounds and all are ok. Another expert said that after those tests the PCM needed to be replaced.

I replaced the PCM, cleared the code and started the engine. The code comes back immediately. I tried this several times.

What else might it be?
Submitted: 4 years ago.
Category: Chrysler
Expert:  Robert R replied 4 years ago.

Hello, My name isXXXXX am a Certified Auto Technician with 25+ years experience. I will do my best to assist you. I don't know your automotive experience level, so I may have to ask questions of you before I can answer. I only know as much about your concern as you have stated in your post, so please feel free to add as much detailed information as possible.

Did you also check ALL the IAC wiring for short to each other? We see this problem a lot because of the harness being taped together so tightly, over time, then insulation of the wires begins melting and the wires can actually touch each other through the insulation... What needs to be done is to actually open up the harness where all the IAC wiring runs through from the IAC as far back as possible and including all the way to the PCM if possible. These wires will need to be actually separated from each other, be careful not to tear the insulation when doing this, inspect wires carefully and tape any suspect areas, or repair if necessary by adding in new wire... then LOOSELY retape the harness wires and reinstall convolute sleeve and carefully route the wires properly as to avoid any future problems....




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Customer: replied 4 years ago.
Hello Robert,

Thank you for your reply. Although I am not a professional mechanic, I have been working on cars for 40 years and have a computer background. I also have a professional scanner that I use.

Now, to answer your question, I have not checked the wires from the IAC against shorting each other. Now that you mentioned it, I should have been smart enough to do that. I will go and separate the wires today and do the checks as you suggested.

One question. If I disconnect the plug to the PCM and measure the resistance between the pins at the IAC plug, would this not tell me if there was a short between the wires?
Expert:  Robert R replied 4 years ago.

Correct, If you disconnect the connectors on both sides of the circuit and test with an ohm meter, you SHOULD be able to tell if they are shorted together. Although, I have in the past, done this and STILL had a problem, so it may still be necessary to separate all the wires to be sure.... The problem is, sometimes, when wires are cold, the contact doesn't quite happen, once the engine is warm, it softens the insulation and at that time the wires may begin actually contacting each other......I have ran into this several times in the past.....


Let me know if you have any luck with this....




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Customer: replied 4 years ago.
Got it. Thank you. I will report back.

I do have an unrelated question that I would like to have directed to you. how can I do this on a seperate request?

Customer: replied 4 years ago.
Ok - here are some interesting resulst. With the IAC plug disconnected and the A plug disconnected from the PCM, I checked all 4 IAC wires. None are shorted to ground or to each other.

Next, I hooked up my scan tool and tried to control RPM via the IAC tests. I could get the 800, 800 and 1000 RPM test to work intermittently, but no higher RPM.

I the took the new IAC motor/valve out and tried the IAC control tests with the KOEO. Lo and behold, the IAC motor moved the pintle in and out properly, every time.

I have cleaned out the dirt from the IAC motor port several times already, but is there a possibility something is blocked or am I going down the wrong path here?
Expert:  Robert R replied 4 years ago.

Hi, on the unrelated question, if you want to open a new thread, You can always request me through my profile at Begin your question with “Robert R" so I will be able to easily find it... OR you can just ask me here if you like, I have no problem with that....


As for your results, after testing the IAC with the KOEO, did you reinstall the IAC and see if the light comes back on?


There should be no issue with the IAC ports being slightly carboned up, you may remove the throttle body and try blowing compressed air through all the ports just to be sure there is no blockages. Although the P0505 directly refers to the IAC circuits, not necessrily if the IAC is sticking or something.


Is this a new PCM? or remanufactured that is installed in this vehicle? Where did you purchase it?

Customer: replied 4 years ago.
Ok - here's what's happened since my last note. Since the IAC cuircut seemed to work fine while being manuall exercised, I figured I would take off the throttle body and clean the IAC port. I used some TB cleaner, then blew compressed air through. Reinstalled everything erased the code and so far I can command any RPM now and the light has not come back. Now whether this fixed it or not remains to be seen, but every other time I cleared the code, it came back immediately.

As for the other question, I already asked it through your profile, on a 1998 Sebring.

Thanks for all the great help.
Expert:  Robert R replied 4 years ago.

Cool, let me know what happens, If it happens to do it again, the next step will be to do the wire separation procedure. The problem may still lie in this area...

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