P0174 - Bank 2 is too lean

[92ShoOff]

So it started off with a misfire a couple of weeks ago. I had code P0301, cylinder #1 misfire. Replaced the #1 coil pack and the car went back to being full of power. A small amount of mileage (maybe 20 miles) was put on the car afterward, and I get another CEL. Took the car to AutoZone again and got code P0174.

I bought some MAF cleaner and sprayed the two MAF wires, following the instructions on the can. Unplugged the negative battery cable to reset the computer, let the car idle for a few minutes and the light came back on.

I'm not noticing any symptoms from this. No lack of power, no rough or unstable idling, nothing. I did just have the intake manifold completely torn apart, but all gaskets were replaced, all bolts were tightened, all hose clamps on the runners are snugged down, and to my best knowledge all hoses are reconnected. The hose coming off the front valve cover was split were it slides over the ******, and I did RTV that when I reinstalled it. It wasn't a long split, maybe about 3/8" long at most, starting at the end of the hose. I'm pretty sure the length of the split probably isn't even as long as the ****** on the valve cover, so nothing should be leaking but that surely is one place for me to double check.

Something else has me thinking that I may have left something out when I reconnected things on the back side of the intake manifold, between the manifold (surge tank) and the firewall. I'll double check that as well, but does anyone else have any other suggestions? Is a bad O2 sensor a possibility or is that not possible with this particular code? Any other advice would be greatly appreciated!!!

 

[SHO Dude]

Proper Diagnostic Routines.

If you don't have access to a scanner that will look at each individual PID value, swap the O2 sensors (Bank 1 to Bank 2) and see if the code moves to Bank 1. If the code moves, you've found the problem. If the code remains, it's not the sensor.

Note: Make damn sure that you're moving the right sensor. Green connectors, not blue.

 

[92ShoOff]

Hey thanks very much for your help!! I luckily didn't even need to get into swapping the O2 sensors around or anything. I re-inspected the small hose going from the front valve cover to the plastic Tee fitting, and the crank was a bit longer than I thought. I cut a new piece of hose, put it in place, reset the computer, and took the car for a drive and no CEL. So that hose apparently WAS leaking. But thanks again for your help Doug. I'm sure with 160k the O2 sensors have probably never been replaced, so when I do eventually get a code for them I'll know what to do!

 

[SHOZ123]

Diagnostic Trouble Codes (DTCs) P0171 bank 1 (Cylinder 1) and DTC P0174 bank 2 indicate the fuel/air ratio is too lean. The fuel trim system is at the rich correction limit.

Fuel system
Contaminated fuel injector(s).

Induction system
Air leaks after the MAF.
Vacuum leaks (vacuum lines and gaskets).

Base engine

Cylinder compression.
Exhaust leaks before or near the HO2S(s).
Check intake air system for leaks, obstructions and damage.
Check for vacuum leaks.

That's what the manual says to check for and I eliminated anything that would affect both banks. You can back probe the O2 wire going to the PCM and measure the actual voltage swings with a voltmeter. Kind of hard to find the wire though on the PCM connector.

Seeing as you are only getting this on the front bank I would think there may be a vacuum leak due to the recent engine work. You could drive a few miles and look at the plugs.

How many miles on the engine?