(the dreaded) P0171 and evap system test never passes

[6stringbass]

I've done quite a bit of reading about everyone's favorite P0171 tonight (did you know you can learn A LOT of useful stuff here?). I'm intermittently getting code but I also note that when I clear the code all other emissions tests pass except the evap system. Have only seen it pass once in the last 4 months or so. Car has 320,000 on it but GM reman engine has only 23,000 (yes there's a story that goes along with the replacement...won't bore you now). I've replaced the gas cap as mentioned in many places. Not sure where to start troubleshooting as I feel both issues affect each other. I could use some sage wisdom here. Thanks in advance and there will be more thanks down the road.

 

[mrrsm]

Your problem might be traced to the SAIS Air Pump Solenoid being intermittently STUCK OPEN AND ON...and consequently, pumping additional Oxygen Rich Air into the Exhaust System.This causes the O2 Sensors to sense a Lean LONG TERM FUEL TRIM problem...and it compensates by throwing that P0171 Code...and mistakenly signaling the PCM to Add More Fuel to overcome the Lean Condition. Once you Replace that SAIS Air Pump Solenoid located on the Passenger Side center of the 4.2L Engine and Clear The Codes... This problem should go away. Here is video that shows all of the hardware involved in the issue ...after explaining this information in much greater detail:

And if you check out this link... You can see the Offending Solenoid on this Diagram as Part #2 in Post Message #4 to get a better idea of what the entire SAIS Hardware set up looks like:

https://gmtnation.com/forums/threads/chasing-gremlins.16430/#post-521349

 

[Mooseman]

What year is your TB? Your profile says 2010, which is impossible.

 

[Kelly@PCMofNC]

Sounds like two independent issues.

1. P0171 is a lean code. Something is causing the engine to run lean. A leak, a bad oxygen sensor, MAF (if you have one), etc.

2. Every time you clear the code or disconnect the battery, you reset ALL of the readiness monitors. EVAP takes forever + one day to reset. I doubt you actually have an EVAP problem (unless you see a code pending for it).

My advice would be to troubleshoot and fix P0171, drive it daily for 3-4 weeks, and go from there. If you can tell me what year this is I can get the GM diagnostic for the P0171 for you to go through.

 

[Reprise]

EVAP takes forever + one day to reset

So *this* is why mine never shows 'ready' in Torque. I haven't waited 'forever' yet
NBD for me anyway; I have no problems / codes, and I was given a 2yr retest date on the Voy last time I took it in for emissions.

 

[6stringbass]

Thanks for the various replies. My TB is a 2006 (not sure how it got set to 2010 in my profile). I understand that resetting codes clears the monitors as I track them after a code clear. The evap test should complete within a tank or two of gas and it doesn't. I haven't seen any codes specifically referring to that.
I haven't looked at the secondary air solenoids but I will. Wouldn't think of those so thanks. I've seen that video too. I learned quite a bit. Also makes me miss the old days when cars weren't large mobile computers. My next goal is to learn more about the various things that can be monitored in Torque and also learn more about what Torque itself can do. It sure does make troubleshooting a bit easier.

 

[Mooseman]

If you're constantly in freezing temperatures, it won't run through the evap (ask me how I know). That is probably why in Ontario, they allow one to not pass as long as you don't have a code set.

 

[Kelly@PCMofNC]

So *this* is why mine never shows 'ready' in Torque. I haven't waited 'forever' yet
NBD for me anyway; I have no problems / codes, and I was given a 2yr retest date on the Voy last time I took it in for emissions.

Yep. Forever and a day to be exact. Seriously though it is a huge PITA to wait for.

 

[Reprise]

Yep. Forever and a day to be exact. Seriously though it is a huge PITA to wait for.

Ok - I'll bite... seriously... how long *does* it take? I've probably got 50+ hrs on the motor since PCM was last reset (via battery disconnect).

Although as of last night, I got my hands on a Tech 2 - and I know I can run diags from there.

I know the system is working - I just don't see it in a state of 'ready'.
I've *never* seen it 'ready', in all of the time I've had the truck (closing on 3yrs; admittedly, it sits a lot)

 

[Mooseman]

In winter below 0c, it won't run the self test. You can do the forced test using the Tech 2 but temp has to be above 0c. I had to do it when my O2 sensors wouldn't go ready. No codes or anything, just takes a really long time. I was able to pass with the O2 not ready and Evap ready.

 

[Reprise]

Yep - I'm good for another 18mos or so, emissions-wise, so I'm not TOO worried about it.

IIRC, my O2s are statused 'good'; it's just the Evap system that this happens with. At least, that's what I see with all of my readers (haven't put the T2 on it, yet...the old owner actually ran one of the shorter tests yesterday - I could hear the system engaging / actuating from outside the truck.)