donbrew

The Problem:
My 2011 LT had a "check gas cap" message and a P0171 "system too lean", which illuminated the CEL.

I am positive the gas cap is tight but I flipped the rubber gasket over and cleaned the filler neck anyway. Cleared the codes, drove the car until the EVAP system test ran. I have been running ScanMaster-ELM in real time mode for several days to monitor another seemingly unrelated O2 sensor problem.

The P0171 came back, the car started funny (like a stumble, then evened out), the P0171 takes 2 consecutive instances to illuminate the CEL. Car is just not feeling right, the Short Term Fuel Trim & the Long Term Fuel Trim are going way up to 32% (normal is +- 3%, LTFT should be close to 0%) and varying wildly as is the #2 O2 voltage. This means that the engine is running VERY rich, not LEAN.

So, I Google "P0171". I find that this could result from
The MAF (Mass Air Flow) Sensor is dirty or faulty Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled.
There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
There could be a vacuum leak downstream of the MAF sensor Possible cracked vacuum or PCV line/connection
Faulty or stuck open PCV valve
Failed or faulty oxygen sensor (bank 1, sensor 1)
Sticking/plugged or failed fuel injector
Low fuel pressure (possible plugged/dirty fuel filter!)
Exhaust leak between engine and first oxygen sensor

Read more at: http://www.obd-codes.com/p0171
Copyright © OBD-Codes.com

So, I opened the hood up (I had no tools with me) and remembered that I had left the hose to the PCV port connected, but not clamped after I did a SeaFoam treatment. Pushed it up tighter but no tools to replace clamp.

I drive off and after a few minutes all of the readings go to completely normal! I fixed it! 2 starts later CEL is off.

Next morning: I go to pull the car into the garage to re set the clamp. "Check Gas Cap" comes on again. Scratch head. Check the ScanMaster, it says there is a P0171 & P0496 pending.

Back to Google. P0496.
Faulty purge or vent solenoid/valve
Plugged EVAP canister
Failed EVAP / fuel pressure sensor Poor electrical connection
Short electrical circuit condition (Hyundai, Isuzu)
Faulty canister purge valve
Blocked vapor canister
Faulty vent solenoid

Read more at: http://www.obd-codes.com/p0496
Copyright © OBD-Codes.com

The #1 O2 Sensor is showing a "normal" waveform. I already replaced the #2 O2 Sensor.
I don't own a fuel pressure gauge or a TechII scanner.
The test for the PURGE VALVE SOLENOID (NOT the Canister Purge Valve) is to disconnect the tubes and blow into it, it is normally closed so if you can blow through it, it is bad. Free flowing air!

Internet time again! AutoZone has Duralast PV443 for $13.99 in stock! The other name brands and GM want at least twice that price. When I got the old part out, I found the parts to be IDENTICAL same casting numbers etc.

After installation:
The CEL went off, the current codes cleared, the pending codes cleared after a couple of starts. The Fuel Trims are now averaging 0% The O2 voltages are acting normal.

Morals of the story:

Names of codes don't mean what they seem to.
Lean does not always mean lean. Sometimes lean means rich.
A stuck open, or intermittently bad Purge Valve Solenoid is a vacuum leak.
Vacuum leak add air to the air/fuel mixture.
When the system thinks it is running lean it adds fuel to the air/fuel mixture.
Not every fault causes a CEL, many need 2 consecutive faults.
Many faults will clear themselves after 2 consecutive passes.
A pending code may not illuminate the CEL, this is important because some things are prevented like Remote Start and Cruise Control when a code is present.
Google can solve many problems.

Oh, and the seemingly unrelated reasons for keeping the diagnostics running were codes (P0420) that had "vacuum leak" and failed "EVAP component" in their diagnosis, but mostly "replace your catalytic converter and/or your O2 sensors.

Now the pedal response is better than ever, I always thought there was a lag.

A friend of mine owns a 2008 LT that had P0171 driving him crazy, after he had his fuel pump replaced it went away I have no personal knowledge of what was done to his car.

Note: The Purge Valve Solenoid is under the hood (P0496). The Canister Purge Valve is next to the gas tank (P0449).

Edi

Thank you man, very helpful, i have the same problem with p0171 code. Two months ago i installed a LPG system in my car HHR LT 2.4 2006, on petrol driving is OK, on Gas start p0171, any sugestion??
Thank you
Edi

donbrew

My wild guess is that when you switch to LPG the pressure in the gasoline tank does not respond the way the computer expects.

P0171 means that there is too much air going into the air horn compared to the fuel. The installer did not do everything they should have. I think there is probably a re programming needed or at least a re routing of tubing.

843de

From looking at other LPG conversion threads on various forums, your P0171 is most likely being triggered by the vehicle's air/fuel mixture going too lean Edi.

I'd suggest returning it to the converter for a recalibration to richen the mixture when running on LPG.

Unfortunately, there aren't many LPG converted HHR's in the United States. Such conversions have never become an economically viable option here, as opposed to Europe with the higher fuel costs and stricter CO2 emission standards.

Oldblue

Thanks for the lesson in code Don very helpful