Hi everyone,

I have a 1999 GXE with a p0505 code that I cant seem to get rid of. I followed the FSM troubleshooting and everything seems to check out. It has power at the IAC. I verified continuity between the IAC plug and ECM harness for each of the 4 circuits. I have 30 ohms for the IAC and cleaned it, but I replaced it just to be sure. While running I have 12 volts at #1 and #4 on the IAC. I get 12 volts on #3 when the A/C is on. I don't know what energizes #6.

Any help on what else could be happening? The code comes back right away.

I have also pulled an 02 code, EGR flow code and knock sensor code. I replaced the knock sensor and that one has not come back. I ordered the o2 and will clean the EGR when I get some time. Could these other codes effect the IAC?

Any help is appreciated.

Runs and idles fine.

Thanks,

 

anytime i do an electronic diagnostics, i first start of with checking ALL fuses and fusible links. sometimes a fuse for say "electronic part" blows and triggers a cel and you might spend all day swapping parts and not realize its just a fuse.

your coolant is topped of and has no air trapped in the cooling system, right?

how many miles on the car?

make sure the sensors on the throttle body are working fine also.

GL.

 

If I understand the valve operation correctly, you should have 12 volts on pins 2 and 4 all the time. To operate the valve, the ECU grounds pins 1,3, 4, and 6 as needed. The 12 volts comes through the ECCS relay which is energized by the ECU.

As a horror story, when the IACV goes bad in the 5th gen Maximas, it shorts out a STA509A chip in the ECU and you have the P0505 until you replace or repair the ECU.

 

Thanks for your post. My logic for any fuses or links is that i would have lost 12 volts in a spot that should have it. i seem to have power so I didnt consider fuses as a possibility. Its still a good idea so I'll check them out.

171,000 miles.

What would coolant level have to do with it? Isnt that a 5th gen thing?

Unless I missed something I only see the TPS on the throttle body but I get no TPS code and it seems to work fine.

thanks for you input.

 

DennisMik-Thanks for your input. I think your right on the operation. (I assume you meant constant 12 volts at 2 and 5). I'll just have to research what to test. I know the ECM deal is a 5th gen thing so hopefully that won't be the case.

any other input is appreciated.

 

I spent some more time on this today. I adjusted the idle again unplugging the tps and turning the idle screw down. It is all the way down but idles great. Not sure if that's right but it works well. It was idling around 900 and I thought maybe the p0505 code was from a high idle. Just guessing. Idles around 750 now. Running out of ideas.

Any other input?

Thanks for any help.

 

P0505 probably is set when the ECM tries to reach the target idle RPM value by moving the valve but fails to get the target RPM.

Since you've checked out the 12V on pin 2, 5; FSM said to remove the actuator assembly with wire harness attached and see if it rotates by turning the key on and off, last step in the engine control P0505 section.

There are several O2 codes. Which one did you get? I got a "slow response" code and disconnect/reconnect the O2 harness connector fixed it.

 

Thanks SVI30

Can anyone else verify that the p0505 code will be set if the correct idle RPM isnt reached even if all components are working? Whats the correct idle RPM? Correct way to adjust the idle?

The 02 code was bank 1 sensor 2 so I replaced the downstream sensor and the code has not come back.

Thanks for the input.

 

Thanks to all that have contributed to this adventure.

I thought I would do a reveiw to see if anyone has any more input.

1999 GXE-getting P0400 and P0505 codes (I will clean the EGR soon)

New IAC
Cleaned MAF and throttle body
IAC does have 12 volts at pins 2 and 5
IAC is getting ECM signals on IAC pins 1,3,4,6 while idling. Seems to idle fine.
IAC motor passes OHM test
IAC motor moves in and out (just a little) while plugged in and away from housing.
Idles near 700rpm
Freeze frame data shows P0505 triggered in closed loop at 750 rpm (idle)

Questions-
1) Would a high or low idle by itself trigger a P0505 code if all the actual components are good?

2) Since this is a '99 is it possible it could blow a the chip in the ECM like a 5th gen? If its blown would the ECM still send the pulses to the IAC?

Any and all input is welcome.

Thank for any help.

 

The IAC drive inside the ECM is actually N channel MOSFETs pulling to GND. If the IAC is moving in and out, it should be fine. However all 4 channels should be working. If you have an oscilloscope, you should see these square wave pulling to GND on all 4 channels.

 

Thanks SVI30

I have a handheld scanner but no oscilloscope. I do get voltage signals to the IAC on all 4 channels so I think its OK. I reset the idle last night and the car just runs and idles great. I think I'm going to give up for now and drive it the way it is. The only issue is the light. Maybe I'll bring it to the dealer at some point to see what they can figure out.

Thanks for your help.