Quick Breakdown:

-The P0505 code is for the IACV (Idle Air Control Valve).
-This is ONLY PRESENT on the 2000/2001 5th gen.
-A fault with this Valve can, and has, caused an internal short within the ECU, which requires replacement or repair, either way, a costly and immobilizing problem.
-The main known cause for this ECU fault is due to a short in the motor and/or breakdown of the seal around the motor that separates the motor from the coolant that resides in the valve.
-A common way to alleviate this potential catastrophe is to do the "Coolant Bypass Mod". Please look it up if you're unsure, when search is back up and running I'll try and put a link here for the DIY. Either way, this modification is highly recommended, most owners have not noticed any signifigant problems by doing this bypass. Some owners who live in colder climates may experience harder starting, and rough idle when temperatures are extremely low.


Onto the diagnostics:
The purpose of me making this thread is to make some of you aware that there is an actual diagnostic procedure here, so before you shell out $250+ bucks on a new IACV, you might want to run through the tests below.

I have had the dreaded P0505 code since I bought the car. I recently met the previous owner, and found out that this code plagued him for all his years of ownership also, and he was never able to fix it. Knowing me as you guys have come to, this presented me with a challenge.

That's right, after about 2 years of ownership, a bunch of mods, maintenence, etc, it took some other guy saying he couldn't fix it to make me get off my butt and make a real attempt LOL.

In either case, I thought I'd share the basics of inspection. I meant to take pictures along the process, but I forgot my camera. If I have to pull it apart again when the parts arrive I'll snap some photos of the test procedures for records.

Copied directly out of the 2001 Maxima FSM, Section 'EC' pages 429-437





It was after the above tests that I found out that I had a "Malfunction B" code. After performing the above test procedure for "Malfunction B",my DTC (SES) came on right away.

Reference Diagram, Harness Connector Designations:





I personally had a good reading of Battery Voltage at terminals 2 & 5, so I moved on:



Please note, for test #3, you need to unplug the ECU harness, they don't really make that clear. You want to unplug BOTH the ECU harness, AND the IACV harness, and test for continuity between them. Basically you're just testing to make sure there's no breaks or shorts in the wires. Make sure to test for shorts to Power, and shorts to Ground after testing continuity.

After test #4, I had no vacuum on the Power steering air control valve. I didn't want to call the game on it so I continued all other testing, but it appears my diagnosis stops here. I am ordering the Power steering Air Control valve.






These tests above, for me, were good.

Please note, if you have already done the coolant bypass mod, test number 8 is easiest if you just remove the IACV motor, there`s only 2 screws holding it. IF YOU HAVEN`T DONE THE BYPASS MOD' YOU MAY LEAK COOLANT BY REMOVING. When done the test, I recommend you leave the motor out while testing for `noise` below. You can actually watch the motor actuate when cycling the key if you just plug it in. This is even better than just listening for noise, you can actually determine if it`s doing the job.




I will update once the part arrives and I can get it installed. Pics to come.

 

Updating cause there's another thread out on this, I installed my Power steering Switch about 2 months ago, and haven't had the 0505 code reappear (knocks on wood).

I will be testing for vacuum existance again once I start driving the maxima (if winter ever arrives).

 

Thank you. This is great! To have all the information put together in one thread like this is a big bonus for the rest of us.

Thanks again for a great job.

 

I should forward this over to Manny he can find a place for it I'm sure.

 

This thread is awesome. Looks like I found my problem (after blindly thorwing about $600 at it): Bad power steering air control valve (step #5).

What threw me for a loop was that my ohmeter was bad, so initially blamed my IACV. when that didn't solve the problem, I eventually tested my meter on the battery for voltage (after stealership was selling me on a bad ECU and mine had absolutely no signs of failure) and guess what - after buying a new ohmeter, my old valve was good! Followed the steps above and when I got to #5, no vacuum on the air control valve.

 

TunerMaxima3000: I don't understand test #4. When I pulled the tube, I got no vacuum either--until I turned the wheel (test 5). How does a car fail #4?

 

You need to re-read it dude. This is where my car failed too. I had no vacuum at test point #4. This indicates a bad PS air control valve.
Note, the coloured section of this test clearly indicates the two conditions you can have during this test:

VACUUM SLIGHTLY EXISTS, OR DOES NOT EXIST

If it exists, it's good, if it doesnt, it's bad. This test sucks, because 'slight vacuum' is almost impossible to feel. Just make sure you're testing really really good before you 'call it'.

My P0505 Related to this thread:
My P0505 has been gone since I replaced it, until a month ago when it popped back up. I cleared it and since hasn't returned. It's possible my IACV is bad now as well, dunno. I bypassed the TB so I'm not horribly concerned about it.

 

This is where I got really confused - test #4 says "vacuum does not exist or slightly exists." Then Test #5 says vacuum should exist when you turn the wheel.

Initially, I got to Test #4 and felt no vacuum, so I promptly ordered an air control valve. After reading TKHanson's post, I re-read everything and re-did Test No's 4 & 5. I have no vacuum on 4 (wheel straight), but I do have vacuum on 5 (when I turn the wheel). I'm assuming that means my air control valve is good?

The other one throwing me for a loop is the test for the power steering pressure switch: I get 5V on the harness plug, whether the wheel is straight or turning - (FSM instructions - see Step #3 below) - don't mean to thread-jack TunerMaxima3000, but I think it's necessarily related.





Step #6 is also confusing. I'm assuming this is testing the pins on the switch, which the only way to do so is with the harness unplugged and as such, it seems to pass the test.

 

I'll peek at that later, hardly a thread jack.

When idling with no load on the steering, there should be SLIGHT VACUUM on the hose.

When it loads up it's full Vacuum.

Is that still unclear??

 

^ pretty clear now, thanks. I felt no vacuum at #4 (no load on steering), but good vacuum at #5 (when I turn the wheel).

 

It's simple to condemn at step #4, because you BARELY feel anything. Just make darned sure before you buy the switch.

 

Ok, I'm going to try something different. I'm going to take a sheet of paper to the tube and see if there is sufficient vacuum to hold that paper in place. If not, NADA. I fear it is so imperceptible that I jumped on the "replace valve" band wagon. Since the PS valve is probably a LOT less, I'd rather replace that first anyway. The stinking Idle valve is expense. I found it for $135 but I fear that is a cheep-o version. I'll let you know what happens from the paper test.

 

ok, I'm back. Paper wouldn't hold, unless I turned the wheel. I then tried the cheek test (not that cheek) and could hardly feel anything. I even put the tube to my bottom lip and still couldn't feel much. Just a slight, and I mean slight, vacuum. Shouldn't there be more than that?

Also, test #6 passed perfectly.

Test #9, which is hard to know what you are really hearing, sounds like a few small clicks happen in the area near the IACV, so I suppose that passes too.

 

^^ I would strongly suggest you get the parts from the stealership at twice the price. Reason being, I bought my first one at AutoZone and it turned out to be defective. At my wrenche's instructions, I got one from Nissan, but AutoZone did not want to give my money back, claiming that the warranty on electric items is exchange only, not refund. It took 4 trips to get my money back.

On test#5, I got enough vacuum to have the hose hold against my finger tip (I put a long hose on there, so I could hold it while turning the steering wheel).

 

Ok, my question to you guys is do I do as #4 failed says and replace the control valve (power steering) or simply replace the Idle Air Control Valve all together?Isn't the air control valve (power steering) far less expensive? Also, just where is that anyway?

 

You need to test each component before replacing, as they are fairly expensive: about $250-300 for IACV,, $100 for P/S air control valve & $60 for P/S pressure switch. The air control valve us behind the pressure switch, by the passenger strut tower. It has 2 vacuum hoses going to it.

 

So you failed step #3, based on what you're telling me. Did tests #4 and #5 below pass?

Assuming steps #4 and #5 passed, you've moved onto step #6, hope this is correct? If you've made it to step #6 and it's testing fine, you're supposed to move onto step #7, which you didn't post.

________________________-

If it helps, I'll explaine test #6, it seems you're unsure of what you're testing. This is also helpful for other stuff on any car, as this is how most sensors on cars work:

-The ECM sends out a "reference" signal. This signal is almost always 5V.
-The 5V runs through a sensor, this sensor has a Resistance Value, and the Resistance value changes depending on what the sensor is seeing
-The resistance of the sensor causes a VOLTAGE DROP, proportionate to the sensors resistance (what position it's in, in this case, Steering [loaded] or Straight ahead [unloaded])
-The ECM receives a return voltage that is 5v MINUS the Voltage drop across the sensor
-This return voltage tells the ECM the sensor's position

In the case of the Oil pressure switch, it's a simple sensor, either it's at 0 resistance or High resistance (open). One position returns 5v and one returns 0V

So when you disconnect the plug, you're jsut taking that "sensing voltage" away, so the ECM doesn't know what's going on anymore. that doesn't stop the switch from working.
The switch will still function unless it's broken.

Steering wheel Turned: No resistance (0 ohms/closed)
Steering wheel straight: High resistance (infinite/open)

So knowing this, you now know that what you're testing on step #6, is the Switch (sensor) itself. If that passes, and your previous tests of the wiring were good, you need to keep testing, step #7, carry on.

 

lol. If you felt vacuum, it's fine. This is why I say this test is super tough to do properly because you can't really even feel the slight vacuum that exists when idling and not turning the wheels. You did the right thing, check check check, cheek
Find a way to make 100% sure there's no vacuum. If you find there is ANY vacuum, the air control valve is probably ok, and move on with your diagnosis.

If no matter what you do, you can't get any vacuum, then the air control valve is bad.

 

If #4 failed (doesn't sound like it did if you got some vacuum while idling), then yes you're replacing the PS control valve.

IACV is one of the last things on the list to replace, which is the reason for this thread. There's other stuff to check first before you 'call the game' and get a IACV, which is consequently the most expensive part.

It pays to do this diagnosis properly.

It also pays to do the TB coolant bypass regardless of this test or any parts you might replace. Cheap, fast, easy insurance to help protect your ECM.

 

You are assuming correctly - I went through all of the tests and they all passed. Heck, I even replaced my temp sensors for giggles. Step #7 directs you to diagnose an intermittent fault. I'll post it up for reference.

 

Thanks, TunerMaxima3000. By the way, can you provide a link to the bypass procedure? I know it is simple but would like to see a step-by-step or at least details so I know what part to buy and make double sure I get the right hoses moved. Thx

 

Is your issue intermittent?

The search feature works.

http://forums.maxima.org/5th-generat...l?ref=esp-link

http://forums.maxima.org/5th-generat...nt-bypass.html

 

Nope. The symptoms are the same (high idle - 1000 - 1100 RPM & mostly 100 - 200 RPM lower when cold), surging between 1500 - 2000 RPM and P0505 DTC - usually SES comes on when car has been ran for a while, then comes to a stop and idles for a couple minutes. Even when SES light is not triggered, code is there as ghost code.

Syptoms have not changed at all.

 

Interesting. I might suggest to re-do the diagnosis again, crossing t's and i's, as it goes.

These tests can be easy to mess up, especially when you don't understand what you're testing or how to test it. For me I had to do it 2 or 3 times until I fully understood the test and what I was testing. Once I had a grasp of it, I was comfortable condemning the air control valve.

If you do in fact fail test #3, then you know that you've got a problem in the wiring or the Pressure switch. If test #3 failed pay SPECIAL attention to tests #4 & #5 those are easy to do wrong

 

Well, my car spent the past day and a half at yet another shop. They managed to drop the idle down to about 900 RPM. They told me they drove it about 15-20 miles and left it idling for a while and the SES has not come back on.

They said they adjusted the throttle and the TPS, but IACV and P/S components tested fine.

Idle is still not at target speed, and it's still surging in the 1500 - 2000 RPM range. They told me I need to drive it a while to have the ECU reprogram itself.

I suspect they simply lowered the idle via TPS readjustment (I can tell it's shifting differently). My new P/S switch is coming in tomorrow, so I'm going to change it anyway just to see what happens and re-check all adjustments & tests.

If that doesn't fix it, I'm at the end of my tether here...

 

Since I got the car back yesterday around 1:30, the SES light has not come back on. This morning I performed the Idle Air Relearn and it worked!

My only remaining issue is the idle surging between 1500 - 2000 RPMs. Also, when taking off slowly from a stop - when it gets to the 1500 - 2000 RPM range, the engine revs up (almost as if it went into Neutral) and settles in at a bit over 2000 RPM. The shifting is off too, (besides the above, it's occasionally slamming into low gear when close to coming to a complete stop) but I suspect this might be because they cranked down the TPS to lower the idle. I'll look into that, but will start another thread, since it's probably no longer related to the P0505 issue.

If the P0505 code comes back, I'll update.

 

Sounds like the shop adjusted your idle via screw without doing the proper re-learn at that juncture.

The idle needs to be re-set, combination of Manual adjustment, feeler gauge, and electronic re-learn. The procedure is in the FSM.

Also, shut car off. start, dont let idle go above 2k for 1 minute. Shut off. Repeat.

This cycles the ECU to scan, if the code is still there, that will set it off. I'm not 100% on this procedure from memory, may want to double check the FSM

 

^Tried the above a few times and it helped a lot, but did not eliminate the problem. Re-adjusted the TPS again (well, my brother did it for me), did idle relearn one more time and bam! She's now purring purrrfect!

Just a note: the surging/ mishifting never caused a P0505 DTC.

 

Nice hope it stays off dude!

 

Looking promising. Thanks for all your help and advice!

 

Just and FYI for someone in the future with Idle issues. Just replaced my IACV, cleaned the throttle body as well. BAMB. Fixed my idle issue. Idles a little fast now but haven't yet reset the idle control yet.

 

Alright- here's a question that I'd be curious to know. Those of you who have gone through this dead ECM/IACV issue and found out you had a faulty steering air control valve- what is/was your history in regards to having to replace the high pressure power steering hose? I'm wondering if maybe the steering air control valve going south isn't sometimes linked to having a bad P/S hose leak

Here's my dilemma; I've had the ECM rebuilt and the technician who worked on it confirmed that the problem was in the IACV circuitry. Knowing that I haven't yet repaired anything in relation to the IACV/AAC, steering vacuum switch or TPS, I'm afraid to plug in the computer in order to (attempt to) run the car so I can fully perform the diagnoses in the TSM for all the parts that might be suspect... How'd you guys get around this? I certainly don't want to fry the computer again...

 

Understanding your concern, I'd chat with the inspecting mechanic. At the end of the day, he is the one who made the call on the ECM/IACV, so if it turns out to be something else, I'd think he needs to chew that one.

As far as the question, it's always possible to test stuff in the less-than-ideal methods, but the amount of work to do it would be huge, vacuum pumps, etc. And at the end of it you'd still have less than accurate results.

You really just need the engine running ot test it properly

 

Well, here's what I feel is a silly question but warrants asking- shouldn't I be able to run the car without risking computer damage if I button everything back up, save connecting the IACV? If I were able to do that, wouldn't I at least be able to see if the computer throws or has stored a TPS code, and I could eliminate that possibility?...I could also then test the steering vacuum switch, so long as I had someone to keep it idling....hmm

 

Yes you can test for vacuum under certain spots but that's all. Not a bad idea, worth a shot, I'd say.

 

I'm gonna try a couple things this evening; gonna get the bypass mod done, re-install everything and try to crank it up w/o the IACV connected. Hopefully, the computer will be working again and I can go from there, based on codes, etc.

 

Well, to be honest with you, I've kinda ended up talking through this issue in two separate threads. But regardless, just to sum up what I said in the other, I got everything back together, left the IACV unplugged and attempted to start the car. Brand new motor mount began buzzing after attempting to start it the first time with the ECM re-installed, then the #2 engine control fuse in the engine compartment blew, so I replaced it w/ a 10A fuse to be safe, managed to get the SES light to come on and was able to read the ECM w/ scan tool. There were no codes stored prior to attempting to crank it w/ the motor mount and IACV unplugged. Attempted to crank it once more and lost the SES light, now can't communicate w/ the scan tool, and blew the ECM fuse again (which obviously explains the light going out and the scanner not being able to communicate) But why?!?! Why's the motor mount buzzing again!? The car hasn't even been run with this new one in; this was the first time I'd ever attempted to turn it over with it connected! I wanna scream.

 

Just so I don't leave people hanging, I ended up disconnecting the rear motor mount and replacing the ECM fuse and the car cranked up and ran just fine. To err on the side of caution, I went ahead and replaced the IACV and have had no problems w/ anything thus far.

 

Forgive this. I'm going to throw some stuff in here for now, I"m doing some tinkering and testing with my ongoing P0505, because it has unfortunately returned.

For now, I'm going to pull together every thread I can find and toss them all here.
I'm also going to toss some pictures in here of the ECU's with fried chips.

http://forums.maxima.org/5th-generat...mous-code.html
http://forums.maxima.org/5th-generat...r-ecu-bad.html
http://forums.maxima.org/5th-generat...ried-iacv.html
http://forums.maxima.org/5th-generat...ounts-ecc.html
http://forums.maxima.org/5th-generat...when-warm.html
http://forums.maxima.org/5th-generat...d-seconds.html
http://forums.maxima.org/5th-generat...ues-p0505.html
http://forums.maxima.org/5th-generat...lized-ecu.html
http://forums.maxima.org/5th-generat...m-01-vq30.html
http://forums.maxima.org/5th-generat...0505-code.html
http://forums.maxima.org/5th-generat...nsmission.html
http://forums.maxima.org/5th-generat...ease-help.html
http://forums.maxima.org/5th-generat...ip-repair.html
http://forums.maxima.org/5th-generat...ed-advice.html
http://forums.maxima.org/5th-generat...rol-valve.html
http://forums.maxima.org/5th-generat...x-not-fix.html
http://forums.maxima.org/5th-generat...iacv-help.html
http://forums.maxima.org/5th-generat...need-help.html
http://forums.maxima.org/5th-generat...acv-issue.html
http://forums.maxima.org/5th-generat...ed-advice.html
http://forums.maxima.org/5th-generat...questions.html
http://forums.maxima.org/5th-generat...-question.html
http://forums.maxima.org/5th-generat...xperience.html
http://forums.maxima.org/5th-generat...n-problem.html
http://forums.maxima.org/5th-generat...need-help.html
http://forums.maxima.org/5th-generat...ave-p0505.html
http://forums.maxima.org/5th-generat...0505-code.html
http://forums.maxima.org/5th-generat...till-have.html
http://forums.maxima.org/5th-generat...898-p0505.html

There's a ton more, but I'm not at home and this computer is running way to slow for this.

and this one also
http://forums.maxima.org/5th-generat...is-thread.html

Pics of the damage in the ECU







Failed 'driver chip' for the IACV in the ECM is referred to as a "STA509A" and the cheapest, quickest route for repair is apparently to have a TV repair shop swap the chip, sounds like something some of them might even stock (the chip)?

I am going to see if I can locate the chip, and get one on the way to me before I pull apart my ECU to check it, but that will be an upcoming check that I'm going to perform here.

TODAY, I disconnected the IACV plug, here's the results:

When idling in Park (NO LOAD) the RPM's go from 1100-1700 up and down and all around. It's not cool.
As soon as I put it in DRIVE (LOADED) the RPM's stabilize.

I went for a drive like this which verified the RPM fluctuation only happens when the engine is NOT under LOAD.

I tried stabilizing the RPM by increasing it to 3000 RPM, but it still fluctuates (when the engine isnt' loaded). This tells me that the ECU is messing with Injector pulses, spark, etc when it doesn't have an IACV plugged in for whatever reason.

Next test is to drive home with it disconnected. I still haven't gotten a P0505 code, even though it's totally disconnected, so I am driving it for 15-20 minutes to try and get the code to appear.

Whether the code appears or not, I'm going to plug in a spare IACV I have at home into the plug. The IACV will not actually be doing anything, just dangling off the harness, and we will see if that stops the RPM fluctuation (I think it will).

That will answer a few more questions as I try to figure this system out in more detail through testing.

Happy sunday.

 

Brother Digikey an mcm both stock that chip its like $10.what fries thise is a out of tolerance spike in current like a hard short when doing the repair bump the traces to see if they are stable.

Also this is a mosfet i think so its best to treat it like a processor and make sure there is heat transfer compound on the back if it has a headsink.