I just replaced the idle air control motor on my 2000 nissan maxima and the check engine light is on and the code it is throwing is P505 for the idle air control motor any ideas

 

Did you replace the throttle position sensor?

 

Have you repaired your ECU or at least checked the health of the IACV driver chip inside ECU? I wouldn't connect new IACV until I make sure the driver is in good condition. If that chip is gone (the usual outcome) ECU still won't be able to control IACV albeit for slightly different reason.

 

+1

 

You should read this thread: https://maxima.org/forums/5th-genera...d-seconds.html

 

No i didn't because the code that its throwing is for the idle air control motor p505

 

Does the car have any problems? like any loss of power? any info can really help solve this

 

Well, that's a bit naive. To find out what the reason for your failure is, you need to educate yourself about the possible causes and interactions (as I suggested above), and that includes the TP sensor. You obviously have not done that.

 

TPS most likely has nothing to do with this, I haven't come across confirmed case it does. Besides, it's easy to check. I think, TPS replacement recommendation was born out of desperation to avoid costly P0505 repair but there's no shortcut in this case- any time IACV gets replaced ECU driver chip should be looked at. I don't see how TPS replacement could substitute that.

 

I agree with your last and next-to-last sentence. However, it's a bit more complicated than you make it.
The IACV can fail for several reasons:

1. Coolant shorts the IACV motor wiring, and the resulting short damages the ECU. This is the most common failure (perhaps 85% of total).
2. The thermo-valve inside the IACV gets stuck open. As the engine warms up, the ECU will try to lower the idle rpm …. the IACV motor will bottom out on the valve seat …. it will keep trying to shut the valve ….. this causes a high amp draw and it will eventually take out the weakest links in that circuit -- the STA509A transistor in the ECU.
3. Faulty or Misadjusted TPS. In a manner similar to #2 above, if the TPS is bad or not adjusted correctly …. the ECU does not know it, it will try to adjust …. draws high Amp …. and eventually damages the STA509A transistor in the ECU. BTW, this is why the people who repair fried ECUs want you to replace both the IACV and the TPS before installing the repaired ECU.
4. Intake Leak either in the manifold or the throttle body. The extra air leads to high idle. Then, the ECU tries to correct it via IACV and over time it burns the ECU chip out.
5. It can be argued that any permanent High Idle condition, which the ECU is trying to correct but fails to do so, may, and eventually will, damage the IACV. Not sure how often this actually happens, if at all.

So, TPS replacement is not a substitute for inspecting both the IACV and the ECU/STA509. However, one should be aware of the possible failure modes, and when doing a repair, understand which failure type are you dealing with.

BTW, I have collected all the above information from various posts on this site. My only contribution is collecting and rationalizing the information other ORG members provided.

 

I haven't found any evidence for these cases besides #1 and even that looks like shorted turn of one of the windings of the motor but since no one bothered to measure inductance it continues to go under 'shorted coil' category while in fact resistance remains practically the same, it's not possible to detect by measuring resistance. In The Thread about IACV nakis mentioned ratcheting mechanism in IACV which sounds like ECU needs to drive coils to the ground for short times only to make a step, it doesn't need to drive them to hold step motor in certain position- ratchet or whatever it is will hold it there mechanically. Based on this I don't really see how anything could be overloaded if the coils are healthy even if ECU keeps pushing it. From what I read it was a theory but even its author nakis didn't confirm it. OTOH someone posted AVPro (company who repairs ECU) analysis of IACV failures where they go on about winding insulation getting weaker during manufacture process. That can easily lead to a single turn short, fall in inductance, chip overload- all we observe. It will be also impossible to detect with test for resistance but such bad IACV will readily fry repaired / new ECU in seconds as we also saw happened more than once.