Hi folks -
I have an 04 TL (213K on it) that I've owned from 45K miles. It's twice in the last few months brought up a P0174 code. triggering the check engine light - fuel metering too lean bank 2. Last time the light was off, it stayed off for a good two months. Each time it goes on, within a day or so, the engine light goes out on its own. My mechanic suspects a bad O2 sensor since the scanner indicates only left bank. But he replaced both left bank sensors less than three years ago - they have fewer than 30K on them. He used Densos when he did it. And the LTFT and STFT numbers I'm getting seem out of range on both sides. Here are the freeze frame readings at idle after a 30 min run:
STFT B1 19.5 LTFT B1 12.5
STFT B2 21.1 LTFT B2 14.8
I'll also note that the throttle body was replaced about 6 months ago.
Thoughts? Might just be coincidence, but it seems the code comes up shortly after a refuel - could the gas cap be an issue? Vacuum issue? (it runs a bit rough but no performance issues or stalling) Fuel pump weak?
Appreciate any suggestions or insights. I can also do another scan for more data, like specific O2 sensor data.

 

Have you watched both O2 sensors data in real-time to confirm they are bouncing around like they should?

In theory if fuel pump, both banks would be throwing a code.....again....in theory. Lean on one bank makes me think intake leak or injectors? Not really sure here.

 

^Injectors would be my first guess.

May not fix the issue, but imo worth running some injector cleaner thru the system and see if that changes anything. Good idea to do that regularly anyways.

 

I do regularly run Lucas UCL through, though I know it is on the mild side for cleaning. Thinking of running some Techron for a tankful. Might it need plugs? Haven't been done in a long time, possibly 70-100k on them.

 

Thanks - I'm going to do another live scan, focused on the O2 sensors. I didn't save all the data last time but have it for B1S2 and B2S2:
Again, readings were similar in both banks (i.e.18.0 for B1S2 and 18.8 for B2S2) and they were fluctuating slightly - regulating and adjusting, it seemed.
V was .65 for B1S2 and .595 for B2S2. That seemed very steady - don't believe it moved at all.
I'll redo - other specific data that would help?

Could it need plugs? They could have 50- 75k on them, possibly more.

Thanks for the help!

 

Well it definitely needs plugs because it's not a diesel.

Sorry couldn't resist.

Serious answer: I would guess (but could be wrong) that you'd also be getting misfire codes in that case. Plugs are usually good for 100k but might be worth pulling and inspecting them. Luckily bank 2 is the front bank so those plugs are easy to access - but I'd replace all the plugs at the same time if/when they need replacing.

 

Thanks - I'll pull one plug and check the gap in that case, but I'm suspecting a vacuum leak(s). No evidence of misfires, no codes, engine is quiet and sounds good. Vibration (consistent with an old rear motor mount) is steady - no hiccups. Only inconsistent roughness is after a cold start, but I understand that's by design with this engine? Won't be able to do a rescsan till next week - will post results then.