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Discussion Starter #1
2009 GMC CANYON 3.7L

Fighting this code for a month now, backstory. I've read countless GM bulletins and done many tests + all threads I've read here.

P0171 comes on ONLY on HOT IDLE with freeze frame data - I've cleared the code 4-5 times and it only comes on after the truck is hot and idling.

LTFT 29.7
Fuel Pressure 43.5
MAF 0.4 lb/min

Drove down to Florida and back over Christmas (5000km) and about a week after I got back I had P0171. Had resonator delete pipe on the truck at the time, put the stock intake back on with no change.

Checked air filter (was bad) and replaced with K&N panel filter. Smoke tested whole intake system from airbox to manifold, no leaks.

Smoke tested both PCV fresh + dirty hoses, brake booster, purge valve line to TB and line to purge valve from canister - no leaks.

I've cleaned the MAF sensor carefully and TB, no change. I've tested the MAF by grounding the yellow wire and the LTFT stays within 0 +/- 5 (signal output wire).

Fuel pump reads 58-65 PSI on ignition (KOEO) and 43.5 PSI hot idle. First O2 is working okay I'd say - analog rhythm ranging from 40 mV to 900 mV and only once did I see it hang on 750 mV for a few seconds then going back to it's analog rhythm.

I've verified there are no leaks whatsoever under pressure, although could it be possible the manifold gaskets or something leaking under vacuum? Being the TB plate is closed and the pistons are still "drawing" in air it creates a lot of vacuum on the manifold gaskets - could they leak under "suction" and not "pressure" when I smoke test it? I've smoked the truck hot, cold, and hot after the code turned on.

My question is why is the LTFT jumping up to it's maximum only at HOT IDLE and throwing a P0171. Anytime I check it after the light comes on with a Snap On scanner, the LTFT is in its normal range. I can't catch it jumping on it's own when the light comes on.

I've limited the options to an intermittent bad MAF (but it doesn't have any MAF specific codes), a faulty pre O2, dirty injectors (from travelling and filling up so to Florida), leaking manifold gaskets (under vacuum), dirty fuel pump strainer (2009 doesn't have fuel filter), or something I'm missing.

If anyone has some sort of information of what I should do before replacing parts that would great! If someone knows which part would be at fault in a situation at mine or some insight I'm missing is great help too!

Thanks for taking the time to read this!
 

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Discussion Starter #2
I have no driveability issues - no rough idle or cold starts. Grey wire to MAP sensor is okay, no problems.
 

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I am pretty sure your Upstream 02 is only supposed to range from 80mv-900mV.

Personally I would start here, what miles do you have on the truck and how many on that O2 sensor?

I have read in a book (back in Auto class in high school) that anything below 80mV is faulty when it comes to O2.
 

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It looks like you have covered just about everything. I'm not sure how this would affect the setting of a P0171 DTC, but the Service Manual mentions "Missing, restricted or leaking exhaust components" as a possible cause. Have you checked the Secondary Air System? I know that it is a long shot, as it normally only operates during a cold start and for a short period of time, but it is connected into the exhaust system. If air was getting through there, at the wrong time, it might cause a lean condition.
 

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2009 GMC CANYON 3.7L

Fighting this code for a month now, backstory. I've read countless GM bulletins and done many tests + all threads I've read here.

P0171 comes on ONLY on HOT IDLE with freeze frame data - I've cleared the code 4-5 times and it only comes on after the truck is hot and idling.

LTFT 29.7
Fuel Pressure 43.5
MAF 0.4 lb/min

Drove down to Florida and back over Christmas (5000km) and about a week after I got back I had P0171. Had resonator delete pipe on the truck at the time, put the stock intake back on with no change.

Checked air filter (was bad) and replaced with K&N panel filter. Smoke tested whole intake system from airbox to manifold, no leaks.

Smoke tested both PCV fresh + dirty hoses, brake booster, purge valve line to TB and line to purge valve from canister - no leaks.

I've cleaned the MAF sensor carefully and TB, no change. I've tested the MAF by grounding the yellow wire and the LTFT stays within 0 +/- 5 (signal output wire).

Fuel pump reads 58-65 PSI on ignition (KOEO) and 43.5 PSI hot idle. First O2 is working okay I'd say - analog rhythm ranging from 40 mV to 900 mV and only once did I see it hang on 750 mV for a few seconds then going back to it's analog rhythm.

I've verified there are no leaks whatsoever under pressure, although could it be possible the manifold gaskets or something leaking under vacuum? Being the TB plate is closed and the pistons are still "drawing" in air it creates a lot of vacuum on the manifold gaskets - could they leak under "suction" and not "pressure" when I smoke test it? I've smoked the truck hot, cold, and hot after the code turned on.

My question is why is the LTFT jumping up to it's maximum only at HOT IDLE and throwing a P0171. Anytime I check it after the light comes on with a Snap On scanner, the LTFT is in its normal range. I can't catch it jumping on it's own when the light comes on.

I've limited the options to an intermittent bad MAF (but it doesn't have any MAF specific codes), a faulty pre O2, dirty injectors (from travelling and filling up so to Florida), leaking manifold gaskets (under vacuum), dirty fuel pump strainer (2009 doesn't have fuel filter), or something I'm missing.

If anyone has some sort of information of what I should do before replacing parts that would great! If someone knows which part would be at fault in a situation at mine or some insight I'm missing is great help too!

Thanks for taking the time to read this!
I know this thread is old as dirt, but did you ever find a fix? I'm having the exact same issues and about ready to get rid of this truck because of it.
 
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