QuestionI have the P0174 DTC showing up on my 04 Santa Fe V6 3.5L. From what Autozone tells me, it's one of my rear oxygen sensors. However further research has suggested that there is a leak in a gasket or hose though we haven't been able to find one. It has had some fluctuations in RPMs while idling but I'm not sure these are related to the DTC. I also just had the belts replaced and the bolt/nut retightened on the crankshaft pulley. Any suggestions where to go from here?
AnswerP0174 indicates a lean condition on bank #2. This could be caused by a faulty *front* (or upstream) oxygen sensor, but more likely there's a different issue. Having a scan tool capable of data and freeze frame readout will be a critical tool in diagnosis.
On this vehicle, there are short and long trim fuel values for each bank of the engine. These values indicate the fuel injector on-time as a percentage of the expected on-time. The fact that the P0174 code exists meand that these values were very large for bank 2. Of interest is whether at the time the code set (freeze frame data), the bank one values were also very large. Also of interest is the magnitude of both values now-- i.e. is this an intermittent problem? Although you only have a trouble code for one bank, the problem can be something affecting both banks, but only one bank was bad enough to store the trouble code.
With this information, we can reason whether the oxygen sensor could be the cause-- it would only affect one bank, it it may be intermittent in nature. This problem could also be caused by a faulty air flow sensor, which is a much more common cause of this code. A third potential cause would be low fuel pressure, but this would likely cause per performance under high throttle. It could even be caused by too much ethanol in the fuel.
Yet another cause could be air leaking into the engine without needing to go through the air flow sensor. This is probably the easiest thing for you to check. Is the bellows between the air flow sensor and the throttle body intact and securely attached? Are there any broken vacuum hoses? Can you hear the engine sucking air-- i.e. a vacuum leak?
If you do not find the problem yourself-- I'm assuming you don't have access to a scan tool capable of giving the data information needed-- you should take this to a mechanic that knows how to do the diagnosis I've described. Otherwise, he'll be doing little more than guessing at your expense-- and many of the repairs which would potentially solve the problem are not inexpensive.
