Hello Fellow G35 Drivers,

It’s been a while since I’ve posted but I always seem to come back to the group of people that give me an honest answer.

The issue I am facing has been the biggest pain and has been going on for about a year now. Like others, I have thrown the infamous P1273 code. On the car, I have an intake, upper/ lower plenum, headers, HFC’s, and exhaust which are the only aftermarket parts that could cause a “running lean” code. I had no problems with the code until I put the HFC’s on.

After doing the remedies outlined below, I can go about 60 miles before the SES comes back on. The light will come back on “high load” driving, “cruise” driving, and even when I am stopped just idling. I have also started data logging the sensor readings with the Cobb AccessPort after about 50 miles to try to capture the data for when the light comes back on.

To try to fix the problem as far, I have:
- Changed the A/F sensors (Upstream 02 sensors) twice,
- Tuned the car to have it run a bit rich
- Replaced the gaskets between the upper/lower plenum (and made sure leaks were sealed)
- Adjusted the MAF sensor tolerances/ trims
- Cleaned the MAF sensor
- Did a full fuel system clean

I have a few more things I can try but I am quickly approaching the end of the list….and patience….and $ dealing with this seemingly “simple” problem.

In any case, some of these “fixes” took care of most of the rough idling I was having but I was wondering if anyone else had this problem and wanted to see how you went about narrowing the possible issues down and identifying the source of the issue. Thank you all in advance, and any help would be much appreciated.

 

Any luck with this? I got this code soon after installing HFC's as well... originally I thought I fixed it by re-torquing my plenum bolts which were loose. I cleared the code and it didn't come back for months. Now it's back... I reset the ECU a few days ago and it came back during my next trip after about 10 miles. I did notice the gas station attendant didn't turn my gas cap to a "click" the last two times I filled up, but I seriously doubt that's the problem. I just clicked it closed and I'll drive it a couple days and see if the SES disappears...

Have you made any headway on this?

 

If any of you have any kind of idle drop while the car is idling, it's a vacuum leak. The MAF sensor cant be fooled. I would also check the 10A fuse next to the foot rest and replace it even if it looks good.

 

Rather than make a new thread on this code, I figured I would add to this one. I got a p1273 code, and the guy at pep boys said he thinks it is transmission related... I LOL'ed out loud because well, a transmission problem??

Any how... From all I have read here and 350Z site, it is likely a leak of some sort.

I DO have a noticable hiss coming from my (catless) test pipe, so could this be causing my code? - I have had the SES code for a few days now, but it never stumbled at idle or had acceleration problems until today...

 

I got this same code last night, I might have to tear into the car and see if anything is loose.

 

I have it now, too. I have an 04 6MT with CAI, 5/16" plenum spacer, exhaust, RTPs, and UpRev Osiris tune. Had the tune for about 3 weeks. Didn't get the code til the weather got below freezing.

Also, just got new Greddy spark plugs, and replaced the valve cover and gasket prior to the tune...

 

Hey man did you ever figure out this problem? Im having the same code pop up p-1273 sensor 1 bank 1, i changed the sensor twice and it keeps popping the same code.I have an 04 g35 coupe stock except for a 5/16" motordyne plenum spacer and an injen air intake. I took it to the shop today and they said that one side is running lean. such a pain having this problem and im hoping you solved it. I really dont want to go to the dealer and get ripped off.

 

I get the same code: P1273.
I was told it could possibly be an intake vacuum leak or an exhaust leak near the o2 sensor.
If it's a inconsistent idle then it's most likely a vacuum leak.
I would test using a vacuum/boost gauge to see what the vacuum reading at idle is. It should be 20 in Hg.

 

I actually took it to the dealer to get it diagnosed $140. They said its a bad cat. They also said its gonna be $1400 to fix there and I was like Okaaaaaay buddy. You can go to any muffler shop for more than half that price. So now I got an excuse for some hfc's yay :-) think ima go with the kinetix smog passing ones. So hopefully that will take care of that.

 

if its idling funny its probably a vacuum leak try taking some brake clean and spraying it around your intake and everything that has vacuum while the car is running if the idle changes when you spray it down you have a vacuum leak there

 

Ok thx. So u spray the upper intake manifold with brake fluid? Or the actual intake?

 

i got the same thing going on. code p1273. ive got a short ram intake, motordyne cat-back and BC suspension and 106k miles. the only thing im concerned about is that i was driving in the recent down pour of rain (i live in MN) to my destination. (hydro planed alot during the adventure, going 70-80 down the highway) once i got to where i needed to be, i turned the car off and it was sitting for about 2 hours. i then started driving home and on the way, the light came on. again it was still raining pretty heavily. once i got home i did a simple hand wave by the cats and i didnt feel a leak (not the best procedure i know) but ive never had this code until now. after reading numerous articles and forums, ive come to the conclusion of a few things:
1: vacuum leak
2: just running lean in general due to some mods
3: possible that water splashed into some crevices? ie: o2 sensors-the electrical connectors to the o2 sensors-in the cats-or just something under the car?...
4: suspension is a little rough on these crappy roads...is it possible that with it being so rugged that something from the intake\exhaust components rattled loose?
5: fowled out spark plugs? (i dont think they have ever been changed)
6: something with the fuel pump\injectors? (again, i dont think anything has been replaced\changed)

after reading all of the forums and posts, the last thing i wanna do is keep buying things people have already done and still have not progress.
ALSO: i have let the car idle a bit, and the idle isnt rough(like jumping of 100rpms) but its not as smooth as it used to be.
BUT any more info, or anything someone has done to clear the code would be helpful.
AND no im not going to run o2 extenders just to get the code to go away.
AND please, criticize any of the 6 options i threw out there.

 

YES indeed lol. but hey now....my clutch is going....so....? eh? lol what do you think?

 

yes so you want to spray down the entire manifold and where it seals you can also spray around your whole engine bay where there is vacuum hoses ie. brake booster the brake clean doesnt hurt anything but you'll know if you have a vacuum leak if the idle changes when u spray it down and idle changes or car stalls.

and tuna try checking your o2 connectors for corrosion

 

I've had the same code pop up on my car P1273. It started before I took my cats out, the code came up, a week later I replaced my catalytic converters with megan racing test pipes. I noticed the car was smoking out the exhaust really bad then i got an oil light, a couple weeks later the car keeps going thru oil quart after oil quart every 1000 miles. Im pretty sure the piston rings are gone and is allowing the oil to get into the combustion chamber then burning it out the exhaust, cuz the engine is all around clean no leaks nothin. I'm almost possitive the rings are the problem, but havent got to changing them yet.