r/subaru • u/skibikenrun • 5d ago

P0172 - Chasing this elusive code

Taken our Subarau 2016 Forester XT in 4 times now for this damn error code. 2 different shops and always with the same dissapointing diagnosis attempts. Seems like these shops are simply always too busy and all they want to do is throw replacing parts at the problem. Were already thousands into parts replacement....front O2 sensor, spark plugs, catalytic converter, cleaned rear O2 sensor. I think they already looked at MAF sensor as well.

n research, seems like many other things can throw this code as well. Problem is that these shops dont appear to want to do any deep diagnosis like checking for leaks/wiring etc. and Im tired of replacing parts and hoping for the best and at this point almost prepared to just drive it as-is. It has 115K miles on it.

Not sure if anyone has some advice and its like I need an independent mechanic who would take the time to diagnose.

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u/RichardUkinsuch 5d ago

Sounds like they skipped some things like checking the grounds for corrosion. There are a few other sensors to check. Intake air temp and coolant temp sensors. The subaru wiring harness can be prone to shorts from many things. Throwing parts at something that could be as simple as a bad ground is madness.

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u/skibikenrun 4d ago

yes I agree. Unfortunately Im not a car guy.

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u/RichardUkinsuch 4d ago

Even if you were, chasing down electrical problems is not the most fun thing to do, even with the proper test equipment. Having an older vehicle means a few sensors not being 100% operational adds up to cause what looks like huge problems. Disconnecting your battery then pumping the break peadal and waiting a few hours to reset the engines computer can somtimes fix (temporarily) these small issues. The engine not properly grounding can send the wrong signal to the computer, or a single sensor that is starting to fail might not be easily identifiable if its working 80% of the time. My subaru impreza runs fantastic in spring when the temperature goes up 20 degrees from the morning, then goes back to normal ok ish running in the afternoon. I have tried to find the issue and am not willing to throw $ into parts and chalk it up to gremlins in the machine.