Took my 99 Ford Expedition to get it's yearly inspection and everything passed except the OBDII test.
It failed on the MIL Commanded-On and I was given a code of P0171, System too Lean in Bank 1.
What are some possible reasons for this, and can it be fixed ourselves or must we take it in to be serviced?
I think a vaccuum leak is likely. Sometimes the MAF is indicated, but leaks are cheaper to look for.
It could also possibly be an oxygen sensor in the Y pipe. You can easily test both of them with an ohm/volt meter.
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