Hi guys,
I am new to the forum and have just bought a 2001 Maxima 3.0l with an automatic transmission. It has the dreaded p0505 IACV code as well as mass airflow sensor code.


When I looked at it before buying it I noticed it already had the mass airflow sensor and IACV replaced. I bought it thinking they just forgot to do the idle relearn procedure. I bought it for almost $1,000 under book value, $2960 out the door at a tiny used car lot. Drove it home and idle relearn procedure never would reset the idle surging from 1,600-1750 rpm's. Pulled the ECM and sure enough, the STA509A chip associated with the IACV is burnt. Not nearly as bad as most of the chips I have seen on here though. The paths on the board leading to the chip were definitely burnt though.


Anyhow. I shipped the ECM off to MYAIRBAGS just outside Atlanta, GA in Duluth, GA. $90 all together including shipping on EBAY. But I fudged up. Forgot to test for why the STA509A chip burnt in the ECM before shipping it off. Took off the IACV and sure enough it was brand new but there was no coolant in it and coolant lines were hooked up to the IACV... Tested it at room temp and got bout 22ohms give or take. tested it again after warming up the sensor a little with my laptops cooling fan blowing on it and got 35.7, 35.7, 36.3, & 36.3. To my understanding from what I have read, this is a good IACV.


MYAIRBAGS did say that I had to replace the TPS and IACV before reinstalling repaired ECM. Is this necessary, especially with the IACV being new and passing the tests and no TPS code? Also to the best of my understanding from the posts this forum and the FSM the car has to be running to test the other sensors? Any thoughts or suggestions on what to do? Any way to to test other potential problem sensors without the ECM?


Thanks for reading and hope to hear from you soon, Jeff.

 

Let me take it one-by-one.

Re. "no coolant in IACV": It looks like the previous owner implemented the "coolant bypass" (aka IACV Bypass). This is a solution many members implemented to prevent damage caused by coolant leaking into the IACV and damaging/shorting the winding. In general, this is a good thing and I would leave it as it is.

Re. "IACV resistance": 22 ohms at room temperature is just right. I would consider your IACV to be good, at least for the time being.

Re. TPS: I have no experience in this area to make intelligent comments. Some posts on this forum suggest the TPS should be replaced, but I am not sure. At any rate, they are right in that it is definitely advisable to repair any component that my damage your ECU before plugging in a new/fixed one (ECU).

If I were in your position, I would do the following:

• If your car has an AT, I would disconnect your electronic engine mounts (they are a well-known cause of ECU damage).
• I would disconnect the battery for at least 3 hours, and preferably for 24 hours. This should clear all codes. It should also enable subsequent and automatic "idle re-learn" by the born-again ECU.
• I would then drive the car. I would check for any new codes or CEL. My hunch is you might be just fine.

 

The ECU repair place is telling you to that if you connect a good ECU to a bad IACV, you will create a bad ECU. The seller figured out the IACV was bad and replaced it. Probably after replacing the IACV, they found out the ECU was also bad and priced a new one from Nissan. After choking on the price, they decided to sell the car.

I don't know why the ECU repair place said to replace the TPS. It is a separate, independent part from the IACV that, should it go bad, will not cause any damage to the ECU. You can test it to see if it is good. Because of the new IACV, it might need adjusting, but that's about it.

Whether they did the coolant by-pass or not doesn't really matter for your question. They replaced the IACV. You tested it and verified that the stepper motor windings are not shorted out.

You're good to go.

The coolant by-pass can be done if you want to do it. I doubt that you will own the car long enough to find out if it is/was necessary. It took 12 -13 years for the original IACV that was made with sub-standard parts to go bad. The new one should have better parts. But the reason for the coolant in the IACV is to help with fuel atomization in cold climates in the first few minutes after the engine is first started.

If you do the bypass, the engine might stumble under load at low rpms when it is cold until it warms up. And it might not. Being in a warmer climate, I wouldn't have a stumbling problem. A lot of guys that live in cold climates have done the bypass and don't have any problems.

maxiiiboy has the original IACV, so he's living on borrowed time, so to speak. It is to his benefit to do the by-pass. If I was in your shoes, with a new IACV and living in a cold climate, I would not do the bypass.

 

Well, I no longer live on borrowed time.

I did my IACV coolant bypass today. I managed to do it without removing the throttle body. It took me a while; this was my second attempt and I can only say the video on Youtube helped me a lot. Even so, I had trouble getting the 3" (or 4") piping back on the throttle body until I finally got the bright idea of heating it up. Heat worked like magic.

I have a brand new AICV (from AIP electronics, $58) sitting in my drawer and I don't think I'll install it unless I get P0505's or unless I experience driveability problems.

 

I let my old IACV sit in my 68 degree house overnight and retested it the next morning and it tested like 160 ohms. Definitely not to spec. Threw it away and I was skeptical of Ebay's cheap IACV, so I ordered a new Intermotor IACV from Advance Auto Parts for $174.99 with discount (normally $224.99). Got my rebuilt ECM back in the mail yesterday. Took it apart to examine their repairs. STA509A chip was replaced, and jumper wires added to the back side of the board. Pretty clean work from what I can see. I installed the new IACV and ECM. Car had no trouble but still idled high at 1,400 rpm's with no CEL. Drove the car around the block for 10 min to perform idle air volume relearn and when I put it in park after getting back home I noticed the CEL on again and the car was surging from 1,600 rpm's to 1,800 rpm's just like before. WTF... wondering if the IACV is operational... I can hear hissing coming from the Throttle Body area so I sprayed it with brake cleaner which did nothing. Could the IACV not be closing and the hissing be from air bypassing the throttle valve through the IACV ports? I am going to see if I can hear it operating while cold when turning the key on. And may thing about leaving the battery unhooked for several hours as suggested in above post. Any other suggestions would be greatly appreciated.
Thanks, Jeff

 

I only took off the IACV motor to test it. There would not have been any coolant in there unless there was a leak. When I installed the new IACV and took off the entire assembly and unhooked the coolant lines going into it coolant did come out. And IDK about the bypass mod in my location. There are several days in the winter that are single digits and below zero in Kentucky believe it or not, so I do not know if I would like it or not.

 

Well, since you shipped your ECU for repair it has already been unhooked for a day or so. I don't think any additional unhooking would help. However, it would be nice to confirm that your ECU has indeed been fixed and that it's good. MYAIRBAGS probably just fixed the burnt transistors but did not do a comprehensive test. Only Nissan dealers have tools (Consult II) to thoroughly test an ECU. In your place, I would ask the dealer to test the ECU for me - for their standard diagnostic fee ($125 here in CA, or about 1hr labor fee). If the ECU is not good: note that Courtesy parts is selling rebuilt and dealer-certified ECU's for about $600 .......

This should take care of the ECU.

Re. the new IACV (the one from Intermotor), did you verify that its resistance and continuity is "per spec"?

Also, before you do all this: you may may want to test/adjust the TPS, as Dennis suggested (see above).

Good luck!

 

Yes, lol as soon as I got the IACV out of the box, I tested it. 22 ohms on all 4 tests. But, however, I took the throttle body back off, took off the TPS and IACV, and scrubbed the throttle body down with a bowl of soapy dawn water and a tooth brush, focusing on the throttle blade and inside the throttle body. then dried the inside best I could with a paper towel and rinsed the whole thing off with carb cleaner and let it dry. Then I cut out a thin piece of plastic out of a package and drilled holes in it for the bolts, and put it between my IACV and throttle body to block off the IACV. I also noticed when taking off the TPS that the bolts were not even tight and It was out of adjustment . Put TPS back on and adjusted the idle screw. Then I put the throttle body back on the car and put everything back together. I reconnected my negative battery terminal and tried to start the car. It turned over but would not start. gave it about 1/4 throttle and it started right up, but would die when I let off the gas. It is 47 degrees, cloudy, and windy here right now, so I am assuming it dies because the IACV is blocked off and isn't allowing any air to keep the engine running at idle. But now on the plus side, no more surging high idle. Going to take out the IACV block off plate and see if that fixes it.

 

Took out the IACV block off plate and put everything back together. Start the car and now it is doing the same surging idle again . Well at least I have narrowed it down to a IACV wiring short... although I hate wiring shorts ... guess I will start with testing the repaired connection on the ECM

 

So, here is my recap of what you did:

• You bought a used 2001 Maxima with AT, and with a just-replaced IACV. The car had a P0505 code and a MAF code (presumably, P0100). The car idled poorly.
• You then discovered that the ECU is bad (the STA509Atransistor was burnt) and you mailed it to MYAIRBAGS for a fix that did cost you $95 (I am quoting the price here for obvious reasons .... ).
• After you received the ECU back from MYAIRBAGS you installed it. At the same time, you purchased and installed another new IACV - let's call it "Intermotor IACV". You tested it for proper wiring resistance (22 ohms) but not for "short-to-ground". After the installation, you took the car for a short (10 min) drive; when you got home the CEL light was on again and the car was surging from 1,600 rpm's to 1,800 rpm's, just like before. (Did you check for any pending codes? ) BTW, I assume that you never ran the fixed ECU with the old IACV ..... !
• Next, you used a piece of cardboard to isolate the IACV from the TB. You also cleaned and adjusted the TPS. With these changes, the surge was eliminated but the car could not sustain idle.
• Last, you removed the piece of cardboard that isolated your IACV. With this change, the car now sustains idle but the surging problem has returned.

I feel you may be jumping to conclusions too quickly (e.g., "have narrowed it down to IACV wiring short", and "testing repaired connection on the ECM"). If I were you, I would:

• Check the codes; clearly, there are codes since the CEL is on.
• Measure the IACV pin-to-ground (i.e. pin-to-IACVbody) resistance, for all pins. It should be infinite. This measurement should confirm/reject your hypothesis of "IACV wiring short".
• Consider paying the dealer $125 to confirm that your ECU is OK (clearly, I have serious doubts about the quality of a $95 ECU repair). In fact, you can ask him to diagnose (but not to fix) the entire problem.

 

Yes, I must admit, I did jump to conclusions. And not that it matters but I used plastic on the block off plate, not cardboard. Tested the 4 wires going from IACV to the ECM and all 4 had continuity, and pins 2 & 5 on IACV plug had 12v when the key was turned on. And I took out the computer again and all the pins had continuity to the prongs on the STA509a chip. So I took the IACV motor out with the plug connected and it buzzed and the plunger vibrated for a second and then stopped, but never moved in or out. Does that sound right? What is keeping this plunger from moving out and balancing out the idle? It tests 22 ohms and acts like it is trying to work. Possibly the IACV is stuck but tests good?

 

You need to check the codes!
If you don't have a reader, get one (for example, ). It's an absolute must if you want to try fixing your car.

You should be aware that to a large degree, it does NOT matter what the IACV does. What matters is "what the ECU thinks the IACV is doing."

 

Code is a p0505, same as before. It comes on after the car is completely warmed up for a little bit. But when car is cold idle does not surge and starts out at a smooth 1,400 rpm's. But like I said before, either something is wrong with the new IACV, ECM is not completely fixed, or something else on the car is telling the ECM to leave the IACV plunger open. Any suggestions are greatly appreciated and Thanks for all the previous posts as well guys.

Jeff

 

I had a ECU/IACV situation much like yours (I started a whole thread on it about a year ago). I went round and round with this problem and had mine repaired by CircuitBoardMedics, not once but twice. My advice, is to have a dealer or shop with access to a Nissan CONSULT II tester do a diagnosis. I wasted a ton of time/money/and headaches to finally learn the reputable ECM repair company I used, twice returned to me a ECU that was just as worthless as it was before I sent it to them. Now I hate breaking down and going to the stealership but they diagnosed it in about 10 minutes with the CONSULT II, and that's my advice to you (they can fully test the ECU and you can't). It's not worth the possibility of damaging yet another IACV or ECU trying to run the vehicle to test or set idle or whatever. Just my 2 cents after thinking about what I would do if I had to do it all over...

 

I am starting to realize that it would be better to take it to the nissan dealer and have them use Consult II to diagnose whether or not the ecm repair was done properly or diagnose whatever else could be wrong with it. They quoted me $110 to either successfully perform the idle air volume relearn procedure, OR tell me why it will not take to the relearn procedure. But they even told me that with Consult II it takes them several tries to get it to work. Long story short it is worth $110 for me to not have the headache of diagnosing this issue anymore. Thanks for the insight it is much appreciated and gave me the extra nudge I needed to take it to the stealership lol.

 

Long story short the new IACV was bad. I warrantied it out at the parts store and plugged the new on in but didn't reassemble everything yet and when the key was turned on and off the plunger actuated in and out. If you recall from my previous post the IACV I just returned to the parts store would only twitch and did not cycle in and out with the key being turned on and off. Reassembled everything and started the car and it ran perfect. The technician successfully performed the Idle Air Volume Relearn Procedure, the advisor up front charged me .5 hour labor for the procedure and I was on my way. However the technician did mention that I may need to adjust the throttle stop screw, which when I was leaving the dealership and got to the stop sign I discovered he was correct as the car died. On the way home any time I had to hit the brakes I had to give the car a little gas to keep it from dying. When I got home I adjusted the throttle stop screw to 700 rpm's and now all seems to be well. Do I need to relearn the closed throttle position since I adjusted the throttle stop screw or since it runs fine as is will it be ok?

 

To recap:
The replacement IACV would only twitch when the key was cycled. Even though it was a new part and tested good at 22 ohms with a multi meter, the new part was still bad.


You need to have the IACV motor out but still plugged in and watch the plunger cycle in and out when the key is turned on and off to determine it is functioning.


Hope this information will be valuable to someone else and save them a lot of trouble and headache and money.

 

I have a similar problem and am contemplating changing the ECU. My plunger does not move, not at all.

Will it work at all if the ECU is bad?

IAC is new and tests good with a meter.

 

If the ECU circuit for the IACV is bad, a new IACV won't work. It's like changing a light bulb when the switch in the wall is bad.

 

Thanks!
That's what I thought too.
I have only had the car for a week and am still very overwhelmed with the strange nuances of the system.

 

Unfortunately even new parts can be bad. Ask any mechanic and they can tell you lol. I would recommend performing all the proper trouble shooting steps in the EC (engine control) section of the factory service manual before repairing or replacing the ecm. Also if the ecm is replaced with a different one you have to take it to the dealership and have it reprogrammed. That is why many have their ecm repaired opposed to being replaced. Had mine repaired at MYAIRBAGS for $82 + $8 shipping and the repair was legit, but they had it for a week though before they shipped it back. But the first thing I would check is that the plunger on the IACV is in fact not properly functioning. Take the IACV motor off but leave it plugged in and have someone else turn the key on and off with a couple seconds in between to give the plunger time to cycle out when on and in when off. If this does not work then I would take the cover off the ecm and look for a burnt sta509a chip. There are a couple other threads on the forum showing you how and what to look for.

 

I just looked at my ECM, on the sta509A chip it has a small bulge on the back and a little discoloring on the 7th leg. Does this warrant changing? Just want to make sure.

 

doesnt sound good, can you post a pic?

 

 

I do repair these $125

 

Hello where are you located?

 

i'm not an expert in these things, but if that were mine i would probably send it off to get fixed. bummer

 

I just got my repaired ECM back. The STA509A chip was replaced by another type of chip. The fix looks legit, but, when I installed everything including a new IACV from ebay, I'm still getting the same high idle ranging mostly between 1,400-2000rpm. And because of this I can't do the idle relearn manually. I can't do the relearn for Car Gauge Pro either.

The ohms for the IACV motor is (21.9 for terminals 1 and 3), (22 for terminals 4 and 6).

12v for terminals 2 and 5 for the harness that connects to the IACV.

There are no vacuum leaks. Anything else I should be checking?

I also noticed the top stepper of the IACV motor doesn't move, it just twitches whenever I turn the key to on and off. I tested this for 2 different aftermarket IACV motors. I'm suspecting this is the main cause of the high idle since there's nothing to close the IACV. Should I just shell out the money to get the Hitachi brand? But I am getting 12v of power from the harness. So changing brands is just a guess at this point.

 

I think you are right - your IACV does not work properly (see post #17, it supports this hypothesis). So yes, I would shell out the money and purchase the OEM/Hitachi IACV. Of course, there is a remote possibility that your "fixed" ECU has some other problem that the repair people did not detect but I think chances are in your favor.

 

What is the number on the chip? Is it STA508A?

 

I contacted the company who fixed it, found them on ebay. But the contact person said I should not be getting a P0505 code again with the ECM fixed with a new IACV. He also said that the ECM is more than likely bad again since the P0505 code has shown up. I took a look inside the ECM and visually it still looks good but I don't know if internally its bad.

But another thing, my replacement 7.5v fuse for #58 was blown and had to be replaced with another 7.5v. The bad fuse happened on the second IACV motor I tested. That mod might have saved my ECM. What could have caused the blown fuse?

 

I took a pic of it but its kinda blurry on my phone:

NEC JAPAN
HPA 1559H
K513B

 

Thanks for the info.

However I can't find any chips that have those numbers. They may be manufacturing codes. Could there be numbers on the other side?

 

No numbers on the back side.

 

Your bad/failed IACV has blown your 7.5A fuse!
When this fuse blows, it's a signal that the IACV failed. I think we can conclude that now, as I have been driving with a 7.5A fuse for almost two years. Has never blown in my car. There is a very good chance that your ECU was protected. At this point, do not replace the fuse again! - not until you obtain a good IACV (OEM only).

 

Yah I'm going to get the Hitachi IACV from rockauto and send in my ECM back to the company just to make sure its ok. Thanks for the help.

 

I also need help with trouble shooting the Throttle Position Switch.

On the 2001 FSM page EC-114

It says to test continuity of terminal 4 and 5 for the Throttle Position Switch. Am I suppose to test the harness connector that connects to the Throttle Position switch or the Throttle Position Switch itself?

 

I agree, the fsm seems vague. But I'm pretty sure they are referring to the TPS itself, not the wire harness.

 

^ thanks.

 

Got a couple more questions. On 2001 FSM EC-434: Check IACV Valve output signal circuit for open and short.

Diagram:


Am I suppose to check the IACV motor and continuity with the ECM harness?

#4 Also check harness for short to ground and short to power.
- Can someone explain how to do this, sorry but still a newbee with electrical problems.