I've had my '08 G35x about a year now. The previous owners beat the hell out of this poor thing- Name even the tiniest most obscure part of the car and I can all but guarantee they screwed it up somehow. That said, after a new rack and pinion last fall it's driven like a dream. I haven't had many mechanical issues with the car- but one.

This spring my service light came on. I got the code pulled (P0171), thought it sounded bad, and saw a mechanic. The first mechanic looked at everything and said it was all fine except for a dirty mass airflow sensor. He cleaned it off and told me I was good to go. A week later the light came back on. I took it back to him and he used a smoke machine- He couldn't find anything. I took it to another mechanic, who also said it looked perfectly fine.

In desperation I made an appointment with the dealership.

The dealership took my car in, looked at it for about 45 minutes, and then told me that 'when these cars idle too long they'll pull out old error codes. That code was actually from 2011." At the time I thought that sounded reasonable, as the light never came on again.

The kicker is, it came back on last night. Let's be honest, at least once in our lives we've taken a car to it's speed limit. On an empty highway late at night, I hit 120 for a few minutes. And once I got home I saw the light was on. I was (irrationally) scared I somehow blew a head gasket or caused a misfire or blew my tranny or something without noticing over the sound of blaring Judas Priest.

I got out the code reader. Lo and behold, P0171. Not sure what going 120 had to do with it, but there it was.

I looked into what the dealer said all that time ago, and I can't find anything about cleared errors coming back. The whole thing just stinks of dealer bullshit to me. Can anyone confirm? Has this ever happened to you?

 

. Well that's a load of bullshit lol...

If the ECM detects that something is an intermittent problem but is not an immediate risk to the emissions control or powertrain then it will store them as a "hidden code" and you can read them with an OBD2 scanner. These hidden codes do not turn on the SES light, they are more of a "well this malfunctioned one time intermittently but it's not causing a control issue so we'll just store it here so a mechanic can look into it next time it's serviced". If the problem is persistent, or if it's a problem with a sensor that is directly impacting emissions or powertrain controls then the SES light turns on so you know that there is a persistent problem, something is broken, get it fixed now.

So, the code, P0171 - Bank 1 too lean. Too much air, not enough fuel. This can be caused by a few problems but since it's only on ONE BANK it's typically either a MAF or O2 sensor problem, or a rip/tear in the intake tract boots on bank 1.

Take apart bank one intake tube, look for ANY cracks/rips/tears/etc in the entire thing, pay particular attention to where it clamps to the MAF and throttle bodies.

Clean the MAF thoroughly.

Check all the PCV hoses to make sure they are tight on their fittings. Nissan likes to NOT use hose clamps on these for some reason so you will likely want to buy some and add them. Unscrew the PCV valve from the valve cover and shake it to make sure it rattles. I think the primary PCV line comes off the bank1 side on the VQ35HR.

Lastly pull the spark plugs on all 6 cylinders, if you haven't replaced them yet or if they have 60k+ miles on them it's probably a good idea to just replace them anyways.

If you can't find an obvious culprit plug into an OBD2 scanner and check for short term fuel trim differences between bank 1 and 2, check for proper O2 sensor cycling on bank 1, compare MAF voltages between the two banks as well. Something is going to be wildly different and it can help isolate what the actual problem is. Ideally use something that logs data so you can get out on the highway under load and floor it while it captures data then you can sort through everything back at the shop. I prefer Torque Pro on my Android phone using a bluetooth OBD2 scanner. It exports everything to .CSV so you can use any spreadsheet to pick through the data and turn it into an easy to read graph. I'm more of a visual person, number people it doesn't really matter.

There are a few various other reasons why it can run lean, not likely for any of these because it will usually make BOTH banks run lean but clogged injectors, failing fuel pump. If you have a single injector on bank 1 going bad it's going to show on the spark plugs, that cylinder will be very scorched, fuel pumps typically either work or they don't work, and when they are failing at high rpm it causes issues on both banks.

You might have a cylinder that's wearing out, a compression test and leakdown test wouldn't hurt but that's typically not going to cause you to run LEAN.

Running the engine hard going 120+ is not going to CAUSE a problem, but you're pushing all these various systems much harder than they would normally experience so anything that's starting to have issues will usually show it when you run them to the max.

 

The mechanic cleaned the MAF and O2 a few months ago, but it won't hurt to do it again myself when I look for cracks this weekend. Thanks for the leads! Not sure what hoses to check though, I'm very inexperienced lmao

 

I don't recommend cleaning O2 sensors, they have a usable lifespan of about 100k before they start to have delays in sending data, if you are getting a lean code it should definitely be on the REPLACE list even if it looks like it's cycling properly when watching realtime data on an OBD2 scanner.

If you want to clean it though just get a small gas resistant plastic container and soak about half the sensor, don't let the harness end sit submerged in fuel though you want the wires up and out of the gasoline. Cover and let it sit overnight then the next day shake the sensor around in the fuel and you should see a lot of residue come out of the tip, pour out the gas, refill with fresh fuel, rinse the sensor AGAIN, let it dry for a few hours, then reinstall.

I also recommend spraying electrical contact cleaner into both ends of the harness to make sure there is no corrosion on it which will skew data. Make sure the can says it's safe for plastic.

 

Can you pull freeze frame data with your scanner? Want to see how the engine was running when it tripped. If it's at idle could be vacuum leak if when the engine is under load could be an injector or something like that.

I recently noticed one of my evap hoses going to the throttle body chewed all to hell. Which would cause a vacuum leak and my car didn't set a code. But I do have high short term fuel trims with no engine codes. These codes can kinda suck figuring out.

 

Use torque pro and a bluetooth obdii adaper to look at the short and long term fuel trims. Post the fuel trims here. Build a smoke tester and pressurize the intake. It may take a few hours building a smoke tester but it comes in handy to find pesky leaks fast.

 

I have a 2009 g37 and it started to idle high around 1100 rpms and i pulled the code p0171 and p0345. It runs great still, it doesnt hesistate, no loss of power, no rough starting,it accelerates well. I cleaned the throttle bodies and it didnt fix it. What do you guys think it could be ?

 

I would go over to MYG37.COM and make a thread there, this website is almost exclusively for the G35.

P0171 means bank 1 is running lean and the ECM has to compensate for too much extra gas, typically this is a vacuum leak or exhaust leak (exhaust leak at the manifold or cats).

P0345 is your bank2 cam sensor, replace it with a new Hitachi or Genuine Nissan Parts sensor, do not use aftermarket brands. Hitachi was the OEM manufacturer for that component.