SOLVED! So begins my P0171 journey.

[sashainwy]

2008 Trailblazer I6. Engine light came on last week. Checked with ELM and Car Gauge Pro. Showed P0171 code. Looked at a few things, didn't know what I was looking for, cleared the code.

Three days later it came back. I checked fuel trim. Short term was bouncing a little over and under 0. Long term showed +18. While I sat there long term seemed to be dropping, might have reached +11. I made no changes and took no action. Two days after that, the code cleared by itself.

Engine idles smoothly around 750. Cruises fine. Accelerates fine. Tomorrow or next day, I'll look for obvious signs of air intrusion, and do the carb cleaner spray tests.

 

[Mooseman]

750 is a bit high, normal is around 650. Yep, check for the usual vacuum leaks, especially around the intake manifold whose bolts tend to loosen over time.

 

[sashainwy]

It's been several days. So since the code came back, and then cleared itself 4 days ago, it has not come back.

Drove into town, upon return, I parked, turned off all accessories, turned off engine and removed key, then started engine, ensured all accessories were still off, waited a couple of minutes, and the RPMS settled to a hair over 600.

Still, I have a plan to a) spray some carb cleaner around intake perimeter while monitor RPMs, and b) regardless of results, torque the intake to spec at some point in the next few weeks. ~s

 

[sashainwy]

Update 2:
Sprayed some carb cleaner around the intake, while monitoring RPMs, and no change.

Scanned again picked up the P0171 as before, but also picked up P0131 and P1133. I might have overlooked those additional two codes the first time, or maybe they weren't showing up before. Either way, they are apparently O2 sensor codes.


Took for test drive and oddly, everything looked good. Idled at ~600RPM, short and long term fuel trims at idle and highway speed looked good. Short term would vary between -5 and +5, long term would stay near +5. Also, live data seemed to indicate that the ecm could see both O2 sensors, B1S1 and B1S2.



Got back, sat in the car for a bit idling, maybe 10 min, then scanned fuel trims for grins. Now they're way off. What the heck! So I think maybe it's a glitch, I drive up the road, and now it shows "open loop" and trims are 0%.



I come back to the house, and check for o2 sensor live data, and I have 0% and 0V for B1S1 (upstream). Maybe without a functioning upstream O2 sensor, computer goes into open loop automatically.


So it seems the sensor is bad, or the wiring is bad. I'm going to order one either way. I'll inspect wiring/connectors, and repair if necessary, and replace sensor. ~s

 

[mrrsm]

Some interesting information here from "The Roadie":

P1133 Upstream O2 Sensor Diagnostics

I keep getting P1133 and P0136 DTC codes on my 2004 Chevy trailblazer with I6 engine. Originally I went to autozone and got a bosch. Yes i know get ac delco. Then i bought AC delco one from rockauto, and that is what is currently in the vehicle. I finally got motivated enough to do some in depth...

gmtnation.com

 

[sashainwy]

Update 3:

Bought an O2 sensor, installed it, cleared the codes, drove it around. Everything seems fine, fuel trims look normal. We'll continue to monitor. Hopefully this is the end of the P0171. (I know it may not be)

As for details, I couldn't find a reasonably priced ACDelco upstream O2 sensor, that I could get my hands on quickly. After some research, I read comments that said Denso is the provider for the original equipment. I went to Napa, and they showed me their OE listed part, and it was in a Denso box. Cost me $20 more than the same thing from Amazon, but I got it immediately and if I had to return it, no probs with Napa.

I also picked up an $8 o2 sensor socket from Napa while I was there. Combined with a 17 inch breaker bar, it worked perfectly to remove the old one, and install the new one.



The other thing is that mom's TB can be left sitting for several days, because she has a backup vehicle. I sprayed the old O2 sensor twice a day for 3 days in a row, with Liquid Wrench. On the morning of the 4th day, I opened the hood, disconnected the sensor wiring clip from the harness, then I jacked up the front end, removed the passenger front wheel, sat in a chair reaching in past the wheel well, used the breaker bar and special socket to break it free, finished removing by hand. Reversed the process with the new one ensuring to use the provided anti-seize.



Afterwards, cleared the codes, warmed it up, scanned for sensor voltage, looked fine, drove it while monitoring trims.



This concludes my P0171 journey. Maybe. We'll see, heh.

 

[sashainwy]

So far, the code has not come back. Knock on wood. ~s