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Old 04-18-2010, 02:16 PM   #1
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Default Jeep will not idle OBD Code P0505

it will run after I rev it what does it mean?
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Old 04-18-2010, 02:42 PM   #2
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The PCM has Inputs and Outputs. The Inputs are from sensors like the temperature and the throttle position and the outputs are for controlling actuators like the IAC motor and fuel injectors.

In the Throttle body the butterfly is completely closed at idle. Above and below the butterfly is a channel or bypass. This bypass is the only way for air to enter the manifold, during idle. The butterfly or throttle valve only opens when you touch the gas pedal. In this channel/bypass is a plunger for controlling the airflow rate. A motor moves the plunger in & out. This plunger/motor combo is the Idle Air Control Motor (IAC). Air for start-up and idling is controlled by the PCM. It tells the IAC how much to open/close to let air into the intake manifold.

Therefore your problem can be only one of two things: a dirty IAC or a faulty PCM. I would suggest spraying out of the throttle body with throttle body cleaner. I would remove the IAC for better access and cleaning. Never move the plunger. It can become damaged easily if you slide it in and out. Try this and if the problem persists swap out the IAC. I rarley ever see faulty pcm
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Old 04-18-2010, 02:51 PM   #3
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as for the pcm there was a recall on my 96 that required the dealership to reprogram it. took it to them and they did the reprogram and i didnt notice a diff but that doesnt mean its not there. just thought i would add that seeing as his profile says its a 96
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Old 04-18-2010, 04:50 PM   #4
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true sometimes they have to flash the pcm I just rarley see it were I'm at.
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Old 04-18-2010, 10:34 PM   #5
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OBD-II DTC P0505 = "Idle Control System Malfunction"

This means that either the IAC is shot, or there's a wiring fault that's not letting a control system signal get to the IAC, or that (least likely) the IAC control circuit in the PCM is blown.

I usually check for wiring faults first. With OBD-II, it's even money on a wiring fault, and probably 5/3 in favour of the part having failed (just often enough that it should be checked anyhow - but OBD will only tell you which circuit has the fault. It doesn't tell you where the fault is.)

If you don't have an FSM (and why not?) you can look up the DTCs that generally apply to us on my site in the Tech Section (culled from FSMs and TSMs.) If it's not there, let me know (so I can add it!) and look it up online.

If your DTC is of the format "X0yyy", it's an SAE standard code that applies to all vehicles. If it's "X1yyy", it's a vendor-specific code and you will need to provide vehicle information (year and make at the very least) when you search for it online. I've heard there are some "X2yyy" codes out there on very late-model vehicles, but I've not yet seen any.

Again, if you don't see it on the list on my site, do please let me know! Give me the code and the year/model at the very least, I can look it up from there if I have to. You may provide a definition if you like (but don't be surprised - I'm going to check it and cross-reference with a few sources I have anyhow. I'm trying to provide an authoritative technical reference for all of us, and that takes some work to make sure of.)

For the formats I listed above, "y" may be any numerical digit, 0-9. "X" may be any of the following letters:
-> P = Powertrain. Usually engine and transmission (and support systems,) but may include later axle sensors and final drive as well. Some transfer cases are also supported under OBD-II
-> B = Body.
-> C = Chassis. Pretty much anything related to steering or suspension here.
-> U = Undefined. These are codes that don't fit under the three previous classifications, are are generally "network/communications" codes.

"0" (numeral zero) indicates an industry-wide code, as defined by SAE.
"1" (numeral one) indicates an "enhanced" or "vendor-specific" code, not defined by SAE. This is why vehicle information is important.
"2" is something I've heard of, but I've not yet seen. Therefore, possibly apocryphal.

The first "y" digit is numerical:
P01 = Emission Management (Fuel or Air)
P02 = Injector Circuit (Fuel or Air)
P03 = Ignition or Misfire
P04 = Emission Control
P05 = Vehicle Speed & Idle Control
P06 = Computer & Output Circuit
P07 = Transmission
P08 = Transmission
P09 = SAE Reserved
P00 = SAE Reserved
(I've listed them this way because this is where the listing typically applies. B, C, and U codes are broken down another way.)

The last two "yy" digits are also numerical, and are used to give the specific fault in the system.

So, if the code doesn't follow the format of: (P/B/C/U) (0/1) (0-9) (00-99), it may be considered invalid and warrant further investigation.

Uncommonly, some code readers will give the code as a two-digit numerical code (like the old OBD-I setup - and all of the OBD-I codes are manufacturer-specific, BTW...) and it can also be given (rarely) as a two-digit hexadecimal number (each digit may be 0-9/A-F, which gives each single digit a value between 0 and 15 decimal, inclusive. Hexadecimal numbering is based upon powers of sixteen, and is a shorthand for binary. Each hex digit replaces four binary digits - and this makes keeping track of internal computer values much easier.)

Fortunately, the five-digit DTC with the alpha leader is most common among OBD-II interrogators, but I've given all three values where they're known (just on the off chance...)
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Old 10-07-2013, 10:54 PM   #6
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Old thread, I know, but I used it as reference to fix my problem.

Just changed my fuel injectors today and when I plugged it all back up I was getting a P0505 even before I cranked it.

Luckily I had a spare IAC laying around just waiting to be installed and that fixed it. Started right up and idled fine. I had accidentally tapped my IAC while installing my new injectors, didn't take much of a tap and it killed it dead. The Jeep wouldn't start until I changed the IAC. I was worried that I had somehow messed up the injector install but the CEL lead me here. Now runs greats with the new injectors and IAC. :-)
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