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Q: Running Lean

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Car was running sluggish and check engine light came on. I went to get a free code pulled and it said Air Mass sensor. So I replaced it. Then it did it again. I took a look and saw the air intake hose just under the windshield had come off the big plastic part. I put that back in and it ran much better but, the check engine light came back on. Now the codes say, P0171 system too lean bank 1, p0101 mass air flow circuit range/performance problem (this is on there twice). It also says it is a MAF sensor wiring. I am pretty good at fixing stuff on my own if you could give me any tips. I have not seen any holes in the hose or anything like that.

My car has 104000 miles.
My car has an automatic transmission.

A: DTC’s ONLY provide clues or an identificati...

DTC’s ONLY provide clues or an identification of the general area in which the fault is occurring. DTC’s can almost NEVER be used to determine which parts are to be replaced, if any are even required. The part, component, or circuit referred to in a DTC has to be separately and exhaustively tested for failure, if any exists.

A perfect example is my own car just the other day. Never set a Code in its life. Was driving along and check engine light came on and stayed on for 2 days. Codes basically said that catalytic converter efficiency was outside design specification and engine was running lean. In my case, got lucky as after first two days the car completely and unexpectedly died (and at the worst possible moment; my son was on his way to a major final exam). Why did it die? The fuel pump died.

But, as it turned out the slowly failing fuel pump, during the prior 2 days, was causing the engine to set a code for both catalytic converter efficiency and running lean BECAUSE the engine was starved for fuel! Note that the Codes did not even "indirectly" identify a fuel pump issue of any sort. Put fuel pump in and ALL Codes disappeared. My point is you have to COMPLETELY (thoroughly) diagnose each code and codes have to be diagnosed in PRIORITY position, too.

Just because 10 codes are set doesn’t mean you have ten problems; instead you often have ONE problem that affects ten sub components, each of which happen to be tracked by the computer so a plethora of codes get set when one thing goes wrong. The bottom line is the ONLY way to properly diagnose the fault you are experiencing is to obtain the Factory Service Manual and follows the diagnostics therein EXACTLY for the Code(s) you are reading (Codes will be prioritized in the Manual). Of course, alternatively, YourMechanic can make make quick work of this problem for you by coming to your home or office and diagnosing the fault for you. Thank you for your question.

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