Ok, I'm busy, but I know that winter will be here before I know it, and the Maxima will be driven exclusively again. I have had P0505 issues since I bought the car, admittedly, I haven't spent too much time trying to fix it.

I will be swapping the IC chip(s) in the ECM at some point, but for now, I'm curious if anyone has any great ideas about how to bypass the IACV, I would need the ECM NOT to throw a code, and obviously would still need the car to idle properly, which I should be able to adjust 'old school' style without much issue, right?


What I am pretty sure I know about the system that is important:

1. The ECM doesn't actually sense the IACV motor's position
2. The ECM knows the IACV motor is doing/not doing what it's being told because of the corresponding changes in RPM and MAFS reading (air flow)

I can't be 100% certain of this, but it certainly seems to be the case. I won't get too far into WHY I am fairly certain this is how the ECM detects it's functionality, but I am pretty darn sure.

Unfortunately because of the way the ECM reads the IACV's functionality, I really have no clue how to bypass it, or if it's even possible.



I might end up just replacing the IC chip(s) and buying a whole new IACV to try and fix this problem, I don't know. But I'd rather not spend the money on a POS that will just end up breaking again down the road again because it's complete junk.
I'd much rather ELIMINATE the problem if I can.

Thoughts?

 

One other option is finding out under what exact parameters the IACV functions. I don't know this.

ie. does it only work then the engine is below operating temperature? Etc?

If there is any parameter that can cause the ECM NOT to actuate the IACV, that would be good info to have. I'm doing this because we now have PLUG-IN emissions tests, and the car won't pass with this code anymore. I need to be able to trick the ECM to think everything is fine, or that it at least shouldn't actuate the IACV for a few days before testing and during testing, that will mean no codes for the IACV.

For instance, if the IACV doesn't function at or above operating temperature, I could simply install the proper value resistor in the Coolant temperature sensor for a few days so that the ECM think's it's at Operating temperature at all times.

After I pass the E test I can put it back to normal and drive the car for another 2 years

 

I like the cut of your Jib --

Regarding your questions I don't know, but I'm wondering if you could adjust your TPS so at 0 mil (the stopper) the rpm was about 700, the same as idle. Not sure if that would still cause a code but seems if rpm's were about right maybe the ECU would be happy.

Or instead of trying to figure out a workaround, if you have time, try to fix it. I assume you've already measured coil resistance and it's ok?

 

lol. Yeah been through the tests but no good results. I've tried a new motor as well as PS switch.

I have to do some checks that aren't listed, like checking for vacuum leaks, etc, because anything that effects the idle will cause the IACV not to work as intended, even though the FSM doesn't list this anywhere I see.

I'll get it fixed eventually, just brainstorming, lol

 

1) The IACV might be a stepper motor, and if that's the case the ECU does indeed know it's position.
2) Yes to all and probably a little more especially if my comment on #1 is true.

The IACV is constantly getting signals to control idle speed. Even turning on the headlights creates a load on the engine and may trigger signals to the IACV. The a/c definitely causes the IACV to adjust idle speed and so does simply turning your steering wheel. There is a pressure sensor on the PS system, that when activated, tells the IACV to increase idle speed. So there are a lot of vehicle operating conditions that will cause the IACV to, well control the idle speed.

BUT - One idea I might throw out into this thread is based upon us 4th gen's (not sure about your 5th gen guys) the Knock Sensor resistor trick.

If the IACV isn't a stepping motor, then the ECU will simply be looking for a current path or resistance indicating the IAC valve (lets call it a motor) is there and may not set a code. However, if the ECU does indeed detect that the idle speed is not being controlled or drops to low it may set an idle speed control P code. (P0505)???

Maybe the way to get around this is to raise the idle speed up to say 850 or 900 with the default idle set screw. (after your figure out how to fake the valves presents) Perhaps if the idle never gets to low, the ECU might not care. Keep those thoughts in mind while your trying to solve your issue.

Good luck!

 

Good thoughts. The ECM doesn't know it's position for sure though, it assumes. It assumes that when it sends voltage to the stepper coils that they are responding as they're supposed to. When the ECM sees that the RPM's aren't responding as they should be if the IACV is working, then it trips the code.

It's an Idle control code, not a low idle code. It senses that the imput to the motor isn't making the requested change in RPM and throws the code.

That's why any issue that would cause an idle fluctuation or problem could easily trip this code also.



If the ECM only needed to know the stepper motor was working, you could simply plug in a good motor, but not install it in the valve, and that would be fine. Unfortunately that doesn't work.

 

Hey guys, we would love to help you by repairing the ECM. Please find complete details regarding our service at the following page:

http://circuitboardmedics.com/maxima-ecm-repair/

Please let me know if you have any questions. I look forward to serving you!

 

Reading this, I decided to do a little experiment on my 2000, which is running OK without any check engine codes.

I unplugged the IACV to see what would happen. When I started the car, the engine was idling at about 1400 rpm and steady. The check engine light didn't come on. The engine was close to operating temperature as I had been driving the car about an hour earlier.

I hooked up my OBD reader and it showed a pending P0505 code. I cleared the code but it came back about a minute later. By now the engine temperature is at operating temperature (199 F) and the engine idle has increased to about 1700 rpm, still steady.

for grins and giggles, I cleared the pending P0505 code several more times but not surprisingly, it would come back.

So a simple unplug is not going to eliminate any codes. I wonder if you got four 22 ohm resistors and plugged them into the harness in place of the IACV, if this would be a suitable simulator.

 

If you look at the SM (EC-331) it is fairly simple what the IACV is doing. As fluid passes thru the IACV the resistance changes. At around 68 degress the resistance should be approx 22 ohms that is why when you disconnect the IACV the resistance sky rockets and the idle goes up.

You would still need to fix the ECM but by putting the resistors there the ECM will always think the coolant is at 68 degrees.

I have seen another post on this forum where what some people do and this only works if the IACV is still functional is just disconnect the coolant lines from it. You would then need to tie the two coolants lines back together. as to nust gush coolant everywhere.

 

The 22 ohm resistor recommendation is great in theory, but if the open circuit is within the ECM (highest probability), the resistors will not complete the circuit, so the P0505 code will remain.





http://circuitboardmedics.com/maxima-ecm-repair/

 

The op knows that he has to get the ECM repaired, it has roasted the STA509A drivers. But if he can avoid replacing the IACV, that would be the bonus he is looking for.

 

I think when the engine is turned off the IACV returns to a reset position such that when you start your car IDLE is purposely high (maybe 1200 RPM), but then fairly quickly lowers itself to target by fine tuning the IACV air bypass channel. But if you disconnect the ECU from the IACV then no adjustments are made and IDLE speed remains at the high default RPM.



Maybe I'm mixed up but just putting in resistors without an actual IACV (or one stuck at the turn on setting) won't allow target IDLE to be reached, and isn't it incorrect IDLE which causes the ECU to flag P0505?

 

I sure seems to work this way. When I shut the car off befre disconnecting the cable, it was idling at its normal 700 rpm. Either the IACV opens by itself or the ECU sends pulses to open up when you turn the ignition key off. Since I unplugged the cable before starting the car, the ECU could not have opened the valve as a starting the engine up procedure.

It is possible that the ECU will issue the P0505 code if the rpm doesn't respond withing a certain amount of time. When I cleared the code it took a minute or so before it came back. I don't know.

Another possibility could be that the ECU senses current flow through the stepper motor. No connection, no current flow. Resistors would allow current flow. Current flow sensing is done to detect burned out light bulbs.

Rpm monitoring does seem more logical.

The FSM doesn't really describe the process very well. The only tidbit of information that I found interesting is that when the engine idle rpm is where it should be, the ECU has to send a holding current through the stepper motor coils to hold the position of the valve, which is why I think the valve opens up when power is off.

 

Like many other members, I have implement coolant bypass for the IACV of my 2000 Maxima. When I did the bypass, I left the IACV in place and simply looped one of the two IACV hoses back to the other IACV port.

I now realize that I did not ensure that there is no coolant left inside the IACV. If such residual coolant is present, the corrosion of the wiring may continue, leading to eventual failure.

I am now pondering how to fix this problem without having to remove & dry my IACV. Any ideas or suggestions ? Those who did the bypass - how did you deal with this issue?

 

Bump. And an update.

I have done more work. After exploring the replacement IACV I happen to have, I came to the conclusion that the "residual coolant" is a non-issue.

There may be some coolant left/trapped in the IACV, in particular if you only drain one of the two coolant ports on the IACV (which is what I did). However, because of IACV placement and geometry, the level of this coolant will be below the level of the seal (o-ring) that protects the stepper motor wiring. For best results, drain the coolant from both ports (Left and Downward-facing) of the IACV when doing the bypass.

 

How does your car idle now that you've done the by-pass, when you first start it up? I just changed my iacv but didn't do the by-pass, but I'm thinking about doing it. I'm just wondering how it affects the idle when it's cold, if it does at all. I know when the coolant warms up it brings the idle down.

 

My car idles just fine - no difference as far as I can tell.

I live in California, but members from Minnesota (and other cold regions) also reported positive results.

 

bump


the coolant that enters into the IACV never touches the control valve unless the gasket has a leak... this an cause the IACV to short, also the strong spray cleaner that is sometimes sprayed into the TB to attempt cleaning can flood the IACV.


************As the coolant heats up, it expands a metal coil inside the coolant housing below the TB baffle and inside the IACV aluminum housing. As that coil heats up it "expands" causing the coil to twist, which then rotates a metal shaft that makes near contact with the magnetic tip of the IACV... in turn the IACV finds its baseline idle.*************


Bypassing the coolant from the IACV only tells the ECU that the TB/engine is not warm enough yet for a much longer amount of time. From my testing the IACV lets something take over the idle at 180*F.


The IACV controls the airflow that bypasses the TB baffle and enters into the IACV air chamber, the IACV piston-like control then adjusts the amount of air that passes through a round opening and into the area of the TB directly behind the TB baffle.

 

I had a BAD experience with these folks. You might have different results but I'm forced to call in a word of caution to all.

 

If your ECU has been damaged, you may want to consider the following outfits:

• AvPro ECM in Fort Meyers, FL (http://www.avproecm.com/nissan.htm). These guys will not only repair ECU, but also they will also improve it by adding fusing protection. The fee is $250, with 2-3 day return and a lifetime warranty. I have talked to them, and they know what they are doing.
• Module Repair (http://www.shop.modulerepairpro.com/...-2000_c801.htm) will repair your ECU for $199.- and ship it back within two days. They advertise the same service on eBay for $99., so make your choice. They are rated 4.5 stars on Yelp.
• Automotive Scientific (aka ASI) http://www.autoecu.com/electronic-co...ol-module-3-0/ This is a larger outfit that will repair your ECU (and many other electronic compon-ents) for $149. Not sure about their customer satisfaction.
• Foreign Auto Computer Repair, Big Sandy, TX. (http://www.foreignecurepair.com/Nissan.htm). ECU repair for $250.

 

http://www.ebay.com/itm/00-nissan-maxima-gle-ecu-ecm-pcm-engine-computer-immobilizer-key-set-a56-p35-z46/141448491708?hash=item20eefcb2bc[/URL]