P0172
 

2010 2.4.
Recently replaced intake camshaft position sensor, and both camshaft position actuators (following whatever codes I had at the time).
Driving to get ready for emissions test. Only the evap system left. Then I get a P0172.
LTFT is around -15%. STFT is normal. Checked at idle, 1500 and 2500 rpms, at 2500, LTFT drops to -10%
Could use some advise on what to look for now. Suspect a vac leak maybe?

Where did you get the camshaft sensor parts? OEM or AutoZone?
How many miles on your front O2 sensors?
How long between parts change and the appearance of P0172?

Maybe a tired front O2 sensor that is unable to sense all of the oxygen in the exhaust. The underreported O2 reading requests richening of the mixture. The mix is identified as too rich. When the fuel trim cannot sufficiently lean it out to within spec, it throws a rich code.

The code is not for the sensor, it is for the rich condition. There are other causes for rich conditions.

If you're reading fuel trim, you probably have a half decent scanner so look at the voltage output of the front O2 sensor. My guess would be it is reading significantly below .6 once warmed up but not enough to throw an oxygen sensor code.

These front O2 sensors last approximately 100,000 to 125000 MI, so if you are nearing that mileage on the front O2 sensor, the timing of the code maybe simply coincidence. If it was a vacuum leak oh, I suspect it would have been an issue all along with respect to codes.

Has your gas mileage been slowly dropping?

Thank you for the help!
​​​​​​First, I only have experience with whatever comes up and I get help from you guys.
last year I did an engine swap on this car. Did the work myself. Engine came out of a Malibu.
oem parts, but I'm not sure if the current code was already there. There were a few codes and I started with what I could replace.
The voltage graph on the O2 sensor looks like a sound wave from a nine inch nails song. Jumping all around.
I don't suppose that's normal...

Oh, I guess that is normal.
I will set up a new test for both sensors and take some screenshots...

https://cimg5.ibsrv.net/gimg/www.sat...2893499953.png

https://cimg3.ibsrv.net/gimg/www.sat...0e2eef8e3c.png
https://cimg4.ibsrv.net/gimg/www.sat...7d91b9d634.png
https://cimg7.ibsrv.net/gimg/www.sat...52ceaff9ba.png

Sorry but I cant really offer much help.
But I am curious as to what scan program are you using.
Looks interesting

Yeah sure.
I use a BAFX Bluetooth scanner I got a few years ago. ( ) It seems to do the trick and is pretty cheap. I don't know how it compares to others or if its even a "decent" tool to use. But it works for my needs so far.
On my phone I use Torque Pro. I have only really used it for the codes until recently. There are many custom displays you can set up, as long as the scanner can get the data I guess...

My two cents - the O2 readings look about right. Upstream is fluctuating (normal), downstream basically steady around 0.7 volts. Seems the ECM is doing what it's supposed to do there. But the fuel trims are definitely showing the engine running rich, which wouldn't be a vacuum leak problem. As you've had issues with camshaft timing, I'd be looking there. Does your scanner have PIDs for desired camshaft position and actual camshaft position? If I remember right, you won't get a code (P001x) until the difference exceeds 10 degrees in exess of a specific time period. But it may be a difference of less than ten degrees consistently, and affecting the air flow through the engine enough to cause the rich condition.

I agree the rear O2 sensor looks fine at 0.7V, and the front O2 sensor is oscillating as it should, the average reading of the front O2 sensor is down around point five ish. So the sensor is not sluggish but it may be poisoned from extended use. I believe the value should oscillate around a bit higher number. Closer to 0.7V.

How many miles are on this front O2 sensor and on the vehicle? I'm not saying the camshaft positioning is not contributing to the issue, only that I believe there is still a possibility that the front O2 sensor reading is involved as it is direct feedback to the ECU to adjust the air fuel mix and for it to be that far off to throw a rich code, I'm thinking it would have to be driven by something that has a very large influence over the air fuel mixture.

Hopefully Andy will read through this and give us his take on the situation. Again the mileage on the front O2 sensor and the vehicle are important to know. Please post.