Maybe someone can help me. I have a 2000 Nissan Maxima GLE 180,000 miles I cleaned my throttle body and then after that my ses light came on with p0505 code and was idling high, so I replaced my IACV with new oem one, nothing, so I sent my ecu out to be repaired they also recommended replacing my tps as a precaution so I did, they repaired it and sent it back and after I put it in I took it to the dealer to do a learn and adjust my tps the tech said he couldn't communicate with ecu so he reprogrammed it then he said when he would try to do the learn it kept kicking him out and into the coolant temp. circuit, and wanted to start trouble shooting so I left and put in new coolant temp sensor, still no change so I sent ecu back to repair company and they said it was testing fine but they replaced components as a precaution and sent it back after installing it I took it to another dealer who could do the learn but the ses light stays on with p0505 code he said he thought it was IACV so I did a parts warranty exchange and installed new IACV and still can't get the ses to turn off tech said probably ecu. does anyone know what could keep the light on with p0505 code or is it just a bad ecu? please help cause ecu's are not cheap. also I have checked wiring and there are not shorts or trouble in wiring and I sprayed throttle body cleaner to check for leaks and can't find any, is there something else? or just bad ecu??????? PLEASE HELP... noone seems to know what's going on

 

Have you checked all the fuses carefully? There are 2 fuses that provide power to the ECU and may have blown. I would expect the dealer would do this.

Your one statement where "the tech said he couldn't communicate with ecu so he reprogrammed it" does not make any sense. If he can't communicate with the ECU, how did he program it?

I do not understand why the dealer does not diagnose the problem. Are you telling the dealer not to diagnose the problem? If the dealer cannot or will not diagnose the problem, you need to test the IACV and verify that the IACV is good. The test procedure is in the Nissan FSM and is easy and can be done quickly.

Then you need to check the wires between the IACV and the ECU for continuity that they did not burn and open up when the original IACV shorted out and caused the ECU to burn up.

If the wiring is good, then you need to get a known good ECU that has been working in a car and install it in your car. Or get your ECU installed in a car that works OK.

I'm thinking wiring.

 

Nobody has mentioned fuses? I will check them and I wondered about tech that couldn't communicate cause they just wanted to start diagnosing at $75.00 hour that's why I went to a different dealer who was able to do the learn and said he could see the IACV which he said my wiring is fine and all I checked in the wiring is with ECU unplugged for shorts or grounds and found none and with the ECU plugged in I got battery voltage on pins 2 and 5 like in the fsm. I also tested original and new IACV and got like 22.7 ohms like in the fsm which would lead me to believe they were ok and maybe just the ECU was bad the whole time, not sure. everything works fine and drives fine just can't get the ses light to go away with p0505 code maybe i'm missing something or just a bad ecu???? other people I have spoke with including the tech. seem to think it's just a bad ECU I just want to make sure before I spend extra on an ECU..

 

Verify that the TPS was installed and adjusted correctly either of which will throw a P0505 and others. The Haynes manual has a good trouble shooting guide on section 6-10. 1st verify correct install of TPS the winding needs to be resting on top of the arm and not under it. Then center the screws and fire it up until warm. The adjustment requires a multimeter and 3 sets of hands to measure resistance and then to dial it in if needed. Not to rub salt into an open wound but you may have been throwing parts into this when the TPS maladjustment from cleaning the throttle body. BTW you didnt screw with the SCREW that rests on the drum trying to adjust the idle? This needs to be set and can be difficult if disturbed. Good Luck

 

When I first installed the TPS it had a little bit of o hard shift but when I took it to the dealer to do the learn the tech. also adjusted the TPS and it seems to be fine now so I would think that by doing that it would be within specs. I don't know if when I cleaned the throttle body that I might have got cleaner in the IACV which may have caused it to short the ECU cause when I tested the original IACV it tested fine with like 22.7 ohms across the pins per FSM. and the repair company that repaired the ECU said they did repair the ECU. I don't know if there might be another problem or if ECU's can just go bad like that. I can't think of anything else and no one seems to have any pointers besides just replacing the ECU..

 

I use "starter fluid" to check for vacuum leaks. Check out the "ECM Fried in Seconds Thread" for a fuller understanding of the IACV/TPS/ECM issue. What about the throttle drum set screw? Did you mess with it? The standard for the '01 is to change out IACV/TSP/ECU and been there and done that! The '01 IACV is junk and I have tested an IACV and across the board test in low 20s and have continuity fail on "a" single pin and have cold start idle issues. The TSP usually creates warm idle, power, and transmission issues and that's why it is important to tune it with a warm engine because of resistance changes and also to verify whether it was installed above the throttle control arm and not below it. The ECU must be repaired as is or you will have to rekey it. If the motherboard is still good I would repair it and it will cost less than $200. if you send out. If not serviceable you must match Transmission and traction with what you have and you will be required to rekey. If a dealer rekeys you will be towing to the dealer and there are some Locksmiths that can rekey it with a Consult II and they make housecalls. Use an 8mm to remove the ECU and be sure to disconnect the negative terminal on the battery before proceeding with any of this. Remove the ECU and the 4 screws and look to see if the STA509 chip is/are fried. Usually you can smell a fried chip before its open. Copy the numbers off the top of the ECU and google to find a rebuilt one. I have had some success with EBAY for rebuilt parts. To summarize: pull battery negative, pull air box, verify TPS is in specification top and bottom, verify ohms and continuity of all IACV pins, pull ECU and check for fried chips, if you have an AT disconnect the Motor Mounts and tapem, get 5/8" hose mender and perform "coolant bypass" of the IACV. Do the TPS relearn if you tune it and the idle relearn on EC67. Good Luck

 

I just used throttle body cleaner to check for leaks I didn't hear any changes and I didn't touch the throttle set screw. And when I checked original IACV I got the about 22.7ohms that the FSM said was good then I checked the brand new oem IACV it tested the same then the tech. said he suspected the IACV so nissan did a parts warranty exchange and I didn't check the new one but it is the 2nd new nissan oem one and it's still the same and I wouldn't think that two brand new oem ones would be bad but the one tested within FSM specs. And wouldn't the dealer have had trouble adjusting the TPS if it was installed incorrectly? cause I had them adjust it and do the air idle learn at the same time. I had sent my ECU to a good rapair company who said they repaired it and when the one dealer said they were having trouble trying to do the learn I had sent it back to the repair company and they said it was tesing fine and that's when I took it to another dealer who could do the learn but just can't get the p0505 code and light to go away also the repair company said they can get me another ECU at an additional cost and any money that I spent having them repair mine they put towards another one that will be gone through and like new condition with a one year warranty. I just want to try and figure out before I spend the money on the ECU if that just could be my problem.

 

Can the ECU be bad and keep the code and light on without anything causing it just the ECU being fried? I don't know that much about ECU circuitry.

 

It is possible that the power steering is causing it. There is an oil pressure sensing switch on the power steering high pressure hose. Its purpose to to tell the ECU that the steering wheel is being turned and that the power steering pump is creating a drag on the engine. This is only important at idle as the power steering pump would cause the idle rpms to drop. So the power steering sensor switch will cause the ECU to increase the engine rpms at idle. A problem in this circuit will cause a P0505 code. If you have the car in gear, are idling like at a stop light, the idle rpm should not drop when you turn the wheels. If it does, this may be your problem.

This is listed in the EC section of the FSM under the P0505 code, either page 510 or page 504, depending on which version of the manual you have..

 

This P0505 is sometimes difficult to diagnose. Because of the relationship of all that stuff piled together in the throttle. 1st, I suggested a continuity check on the IACV as well as verifying the TPS on page EC-116. I have personally tested a 1month old IACV and have it feedback the low 20s ohms test and then tested for continuity and found a degraded pin. My multimeter produces a buzz when testing continuity and this one pin sounded off differently. Changed out IACV and reset TPS and all is well.

*You may also want to verify the voltages coming to the TPS and IACV just rule out the short. Good Luck

 

I haven't checked motor mount wiring for any problems, I did unplug my mounts before installing ECU after it was repaired I'm just not sure if maybe the ECU is just bad other then what they repaired. It drives fine runs fine idles fine at about 750 rpm I did check wire with ecu unplugged and found no shorts or grounds but and with ECU plugged in I was getting battery voltage on pins 2 and 5 which according to fsm I should be getting. didn't do cont. test from end to end of wiring but the tech. that did the learn said he could communicate with the IACV which tells me there is no opens cause the learn took and he set my TPS which tells me that was installed correctly. I'm just trying to figure out if I just need to replace my ECU, I just hate spending the money if it might be something else????? Thanks for all the input...