Contour Enthusiasts Group Archives Forums General Troubleshooting P0174 Question (Yes I searched)

So I got a P0174 (Bank 2 Lean) code last week. That was the only code, there was no corresponding code for bank 1 being lean as well. So i did a lot of searching and came up with a list of possibilities

• Bad upstream o2 on bank 2 (reading lean)
• Leaky UIM/LIM gasket on the front bank (bank actually is lean)
• Some other crazy way unmetered air could get into only one bank of cylinders
• Intake leak
• Bad IAC or MAF
  

So after reading some more old threads it seemed that either of the last two would cause codes for both banks being lean, so I put those as the least likely.
I decided to pull a plug from each bank today and have a look, as I figured that would tell me whether or not the bank is actually running lean. I have pulled the middle plug from each bank (cylinders 2 and 5 i suppose) and not only does the front bank plug not look lean, but the plugs from both banks look identical.
these plugs look just a tad lean to me, but my plugs were not that white on the tips.

So, if you have made it this far, here are my ?s.
1)Have I done anythign wrong so far.
2)Is there any way to test whether an O2 sensor is working properly or not without replacing it. I don't have anything I can monitor A/F with as I am driving, but i know that the o2s put out voltages, is there any tests I can do with a multimeter that would give me a hint as to whether or not the sensor is in working order
3)Am I missing any other possible causes that I need to look into.

Thanks,
Cameron
me

upstream O2's will pulse from low voltage to high voltage (just at 1 volt, IIRC??) fairly fast.. a digital meter will be hard to capture, or diagnose the pulsing. an analog meter would be much better. The swing will be from "rich" to "lean".

The down stream O2's will pulse but much much slower, and less of a swing (the cat acts as a "buffer")

Unfortunately, even testing them wouldn't tell you anything if the sensor is marginally bad, or still operating (just not correctly) You would see the pulsing, and that's all you could tell. the only way testing it would be beneficial is if the sensor isn't pulsing at all. You could definitely tell that.


Ray

If you are looking for something else to do before replacing the front upstream oxygen sensor, swap the two upstream sensors and see if the code follows to the other bank.

Yes, I know that getting the rear one is a [censored], but that will pin it down for you.

From Ford TSB for P0174.

Fuel System:
�· Contaminated fuel injectors
�· Low fuel pressure or running out of fuel (fuel pump, filter, fuel supply line restrictions)
�· Vapor recovery system (VMV)
Induction System:
�· MAF contamination
�· Air leaks between the MAF and throttle body
�· Vacuum leaks
�· PCV system concern
�· Improperly seated engine oil dipstick
EGR System:
�· Leaking gasket
�· Stuck EGR valve
�· Leaking diaphragm or EVR
Base Engine:
�· Exhaust leaks before or near the HO2S
�· Secondary air concern
Powertrain Control System:
�· PCM concern