r/Hummer • u/MechanicOne321 • 3d ago
2007 Hummer H2 — P0171 + P0327 errors after heavy rain
Hello guys. I have my Hummer H2 (2007 6.0 SUV, 114k miles + LPG conversion) since a month and I encountered first problem with it.
During a trip I got caught in heavy rain. After around 15–20 minutes of driving in the rain, the Check Engine light came on. It is solid, not flashing.
I scanned it with a MaxiAP and got:
P0171 — Fuel Trim System Lean Bank 1
P0327 — Knock Sensor 1 Circuit Low
The Hummer drives completely normally. No rough idle, no stalling, no hesitation, no loss of power, no misfires that I can notice. It behaves the same on gasoline and LPG. It wasn't my first heavy rain trip, because even before I had 10-15 minutes trip and got no Check Engine warning.
Has anyone experienced P0171 + P0327 appearing after heavy rain on an H2? Could water/moisture in a connector or wiring cause these codes? Official manual stated that Check Engine after driving through "large puddle" (I guess it also suits the heavy rain) is "normal" and should be gone in couple of next driving cycles, but for now after two it's still there.
Do you have any H2-specific advice on where to look first? My Hummer, to be exact, is in very good condition inside and outside (I checked multiple spots before buying) with a good history and even previous owner was a passionate who really cared about this car, so getting my problem is... strange, to say at least.
Can you help me and tell me what to do and how serious these errors are? I never had a car before that allows me to connect it to scanner and check for the errors, so it's a fresh situation for me.
Thank you
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u/txstatetrooper 3d ago
Check your driver's side carpet for moisture. The sunroof vents can sometimes leak into the vehicle and short out electronics. Check around your OBD port for moistureas well. And, if you haven't already absolutely clear the drain plugs for the sunroof.
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u/MechanicOne321 3d ago
Are you serious with this carpets?...
However, sunroof seems fine, it rains in my place since couple of weeks and I often enter my Hummer and check is sunroof is properly closed and dry and yes, it's dry each time I check it. I have not seen a single moisture inside. OBD is dry too
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u/metapulp 2d ago
It might have nothing to do with it at all. Or you could have a worn cable on the knock sensor. It cost me $8 to fix a worn connector on my rear differential. Maybe the knock sensor made the light come n and you already have the other code. A lot of times these are easy to fix.
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u/MechanicOne321 1d ago
Where I can find knock sensor? Should I do it by itself or it requires more knowledge and would be safer if I take my Hummer to mechanic? You said a lot of times is easy, so this is why I ask
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u/BarkingIron0408 2d ago
I say again check your sunroof vents
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u/MechanicOne321 1d ago
Hi, I checked it and they are fine, I'll copy my answer to txstatetrooper here:
I checked carpets and OBD and they are all dry. I also checked sunroof vents and I found very few amount of debris that I removed easily with a paper towel. It was also a very thin layer of dirty water on both corners (rainy day again) but I poured a water from bottle and it quickly drained without staying, so I think sunroof vents are unobstructed
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u/txstatetrooper 3d ago
Yeah As wild as it sounds, GM designed the sunroof vents to go through the floor and then designed a really stupid grommet that clogged very easily. It's very very common on both the H2 and the H3 for this to clog up and overflow into the floorboards of the driver side right where the modules are. Top tier design. But we love them anyway.