Hyundai Repair: 2003 Hyundai Sonata, air flow sensor, 2003 hyundai sonata

Question
We have a 2003 Sonata and the engine light came on, the code is reading PO171

Can you tell us what is needed for the repair

Thank you

Answer
Hi, Howie.  Unfortunately, I cannot tell you what the specific cause of this code is; there are too many potential causes for me to pick just one.  What I can tell you is that P0171 indicates the engine control module (ECM) needs to keep the injectors on longer than expected to achieve the proper feedback from the oxygen sensor.

If you have a six cylinder engine, a scan tool capable of reading current data and freeze frame data will be valuable.  This is because each bank of the engine has separate fuel compensation.  From this data, you can determine whether the problem is affecting just one bank or both.

Here are the common potential causes:
1.  Unmeasured air entering the engine.  This could be caused by a vacuum leak or a leak in the air bellows between the air flow sensor and the throttle body.  This causes the ECM to erroneously think the injectors should be on a shorter amount of time than is actually necessary.
2.  Faulty upstream oxygen sensor.  This will provide erroneous fuel mixture information to the ECM.
3.  Faulty air flow sensor.  This will under-report the amount of air entering the engine, causing the same situation as case #1 above.
4.  Excessive alcohol in fuel.  It takes a larger volume of alcohol than of gasoline to operate the engine.  Hence, the ECM will keep the injectors on longer to deliver this additional amount.  If the additional amount of on-time is excessive, P0171 will set.