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Old 01-09-2014
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P0174 (Left bank lean)

Hey guys,

I am trying to diagnose what I need to replace so I can pass emissions. I am throwing error code P0174. From what I understand, it can be the MAF or an O2 sensor. Below you will see images from my cell phones (torque app), which is bluetoothed to my ODB sensor. These readings are 30minutes into a drive.

My 1x2, and 2x2 02 sensors are pretty much stuck at constant voltage. Which is causing the fuel trim reading to be off? Should I just replace all the 02 sensors? Truck is a 2002 4.0 SOHC with 125k.

This is at an IDLE at stop light:

This is cruising at 55mph:

Last edited by Todesengel; 01-09-2014 at 12:37 PM.
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Old 01-09-2014
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Location: Vancouver, BC
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O2 sensors on the exhaust manifold, these do the lean/rich for computer
Bank1 sensor1(1x1)
Bank2 sensor1(2x1)

Then for the cat converters you have
Bank1 sensor2(1x2)
Bank2 sensor2(2x2)
These tell if cat converters are cleaning up the exhaust

Bank 1 sensor 1 and 2 look OK

The bank2 sensor2 1.3v O2 sensor is for the cat converter is showing very rich
While O2 for exhaust on that Bank is showing very lean, so I would replace the Bank 2 sensor 1, it looks to be causing the computer to run that bank too rich, and that is causing the 1.3v on the cat sensor on that side.
It could be a vacuum leak on that bank, check the intake manifold bolts make sure they are tight, or spray carb cleaner around while idling, engine will change RPMs if it sucks in carb cleaner.
Exhaust manifold leak on that bank could produce the same thing, it sucks in air which makes O2 sensor see lean.

The Cat O2 sensors usually last the life of the vehicle, they get less build up since cat is cleaning exhaust up, hopefully, when it gets to them.
So only the front O2 sensors need to be replaced, my '94 4.0l still has original O2s, and they are still working fine, 300k miles

For the front O2 sensors you want a steady .5/6 while cruising
The rear O2s should be just below front O2 voltage

I would also check your scan tool on another OBDII engine, the idle O2 readings look odd

Last edited by RonD; 01-09-2014 at 11:10 PM.
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