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Discussion Starter #1
Hi all. Working on my wifes 2013 malibu ltz 2.0 turbo. Has had the infamous P0171 code since a week after we bought it. Now also setting a P0449 code and needing to replace one of the rear hubs. Anyway, I have checked the MAF, replaced both 02 sensors, checked for vacuum leaks and continue to be eluded by the 0171 code. Does anyone have the torque spec for the intake bolts? I have seen a few mention that retorquing them solves this problem sometimes.

Also, replacing the canister vent valve solenoid on the tank for the 0449 code. I am guessing thanks to its location, the tank has to be dropped to replace. Is that correct?

Appreciate any help. Happy wrenching.
 

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I don't have specs for the 2.0 , my car is a 2.5 but here's a diagnostic aid from alldata for the 171. You may be right on intake being loose. Purge valve may be on the engine as there is one on my 2.5. I'd recommend a Alldatadiy subscription for doing your own wrenching.

Conditions for Clearing the MIL/DTC

DTCs P0171 and P0172 are Type B DTCs.

Diagnostic Aids

- Allow the engine to reach operating temperature. With the engine running, observe the HO2S parameter with a scan tool. The HO2S value should vary from approximately 40 mV to approximately 900 mV, and respond to fueling changes.

- The normal Short Term Fuel Trim and Long Term Fuel Trim parameters should be between +10 and -10 % with 0 % the optimum, with the engine running at operating temperature.

- Any un-metered air into the engine causes this DTC to set. Thoroughly inspect all areas of the engine for vacuum leaks.

- A MAF sensor condition can cause this DTC without setting a MAF DTC. If there is a MAF sensor condition, the MAF sensor parameters will appear to be within range.

- Verify that the air filter is the correct one for this application. Verify that the engine oil fill cap is in place and that it is tight. Verify that the engine oil dip stick is fully seated.

- Certain aftermarket air filters may cause a DTC to set.

- Certain aftermarket air induction systems or modifications to the air induction system may cause a DTC to set.

- Certain aftermarket exhaust system components may cause a DTC to set.
 

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Discussion Starter #3
Thanks for the response. While all of that is helpful info, I have replaced both 02 sensors and they are both performing as they should now. Cleaned the MAF and it typically reads around 3 g/s at idle. Have checked all visible vacuum lines, connections, etc. both visually and with throttle cleaner (unfortunately don't have a smoke machine) to verify sealing. Air intake and exhaust are both OEM. With the 2.0 being a turbo, it leads me to believe that a. there is an internal issue with the turbo feeding too much air/fuel (misadjusted/worn inlet valve or similiar turbo part) b. a very minute vacuum hose leak that is just enough to upset the balance without a noticeable difference being sprayed with carb cleaner c. Intake isn't properly sealed allowing air in. Freeze frame data for when the code was set shows the long term ft at 30%, which is a ton of fuel leading me to believe it is vacuum related. However, it's worth mentioning that the time it takes for the code to come back after reset has varied greatly from same day to sometimes several weeks. It seems to be an intermittent issue, but an annoying one all the same.

Hoping someone can provide the intake bolt torque spec still to verify they are properly tightened.

Also just making sure the tank must be dropped to access the evap canister vent solenoid before tackling the hassle of doing so.

There doesn't seem to be alot of service related data available for the current models, especially the 2.0.

Thanks for any help.
 

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Discussion Starter #4
Found an OEM service manual at a good price. Wanted to post this for future users who may need it.
68094
 
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