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My check engine light has been on with p0171 and p0174 lean codes for over 150 miles after installing a cai. As mentioned in a previous post I have been awaiting a new intake tube fro k&n. Well today I filled up my gas and the CEL goes out, not sure if it was right after filling up or not. When I connect my intune to read the trouble codes it still lists active codes as p0171 & p0174 even though the CEL is extinguished. My question is will the codes always be present once the computer triggers them or should they automatically clear once the CEL goes out?
 

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From what little I know, the codes will remain stored until cleared. By a scan tool or similar device. The check engine light in some cases will go out on it's own after a certain number of run cycles, regardless of the issue being resolved.
Those codes were most likely from an air leak somewhere.
 

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Krank said:
Thanks for the response. So my CEL will go out even if the problem is still happening?
If the fault(s) causing the CEL are no longer detected, the CEL will eventually go off but the codes will be stored until erased with a tuner or tool.
If the ECM later on detects the same unusual/abnormal conditions, it will turn the light back on.
 

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Krank,

I am sorry to learn that you are experiencing an issue with your vehicle. I might not be able to give you any technical advice but I would like to look into this concern for you. Please private message me if I can be of any assistance.

Safe travels,

Jennifer T.
GM Customer Care
 

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I had this problem on my 2002 Impala. It was dirty injectors. The dealer told me that sometimes just changing the fuel filter on that vehicle takes care of it.
How many miles since you had the injectors cleaned or replaced?
 

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Those codes are for lean condition on bank 1&2. Normally I would say you have a bad upper plenum gasket but since you said you just replaced the intake you have a leak somewhere after the mass air flow sensor. Check your pipe connections and the new intake tube for a leak or hole.
Did you run the engine with the system partially removed? That could also cause it.
The CEL will not turn off on it's own if the condition still remain regardless of the amount of run cycles you perform. If the light went out that means the ECM is seeing everything as functioning normally at this time.
 
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