Hey all! 2005 Ford Ranger 3.0 Edge, automatic, rwd. I've got two P0174 codes - one stored and one pending - both stating that the system is too lean on Bank 2. I confess I'm not yet that familiar with my scan tool, so I don't understand a lot of the information, so I just thought I'd share it and ask if there's any suggestions for diagnosing what's going on. The truck is running fine, but really is drinking fuel more than usual. Both codes were apparently triggered at startup - which was slightly rough, but not enough to worry me except that the light was immediately on.

So, the STFT B1 is 5.4%. LTFT B1 is 17.9%. STFT B2 5.4%. LTFT B2 20.3%. MAF 0.46 lb/min. TPS [what is this?] is 17.2%. O2S B1S1 0.580(v). STFT B1S1 [What's this?] is 5.4%. O2S B1S2 0.495(v). STFT B1S2 99.2%. [what does this mean?] O2S B2S1 0.150(v). STFT B2S1 5.4%. O2S B2S2 0.545(v). STFT B2S2 99.2%.

I thought the Ranger only has 3 O2 sensors; does it actually have 4? Any suggestions greatly appreciated, thank you for your help!

 

OK, lets start with some basics

STFT = short term fuel trim
After engine is warmed up the O2 sensors start to work, they need to be above 600degF to work
The computer's job is to calculate how much fuel to add to the engine at any RPM and any LOAD
And that calculation is the OPEN TIME for each fuel injector
And that's expressed as STFT 0
STFT +5% means computers calculation was off, so its now opening each injector 5% longer than it has calculated
STFT -5% means calculation was off so its opening each injector for 5% LESS time than it calculated

LTFT = Long term fuel trim, because any engine will change over time the LTFT is an average of STFT over time, so the computer doesn't have to "relearn" the system every day
Your B2 LTFT of +20% is why your computer set the P0174 code
To see true fuel trims you add STFT(+5%) to LTFT(+20%) which in this case would mean fuel being added is 25% over what computer "thinks" it should be

O2 sensors see OXYGEN only, not fuel
O2 sensors are designated as Bank 1(B1) and on a "V6 or V8" engine Bank 2(B2)
AND by location, Sensor 1(S1) is the upstream O2, closest to the engine
Sensor 2(S2) is downstream O2, after Cat converters
On Fords Bank 1 is passenger side of engine, so Bank 2 is Drivers side

B1S2 would be passenger side downstream O2 sensor
Dual exhaust would have B2S2, and some single exhaust also have B2S2
If you see 99% from an O2 location that means that sensor doesn't exist or is broken or bad wires

O2 sensors use a chemical to detect oxygen and they run out/use up that chemical, 100K miles or 12 Years which ever comes first
Your 2005 is 16 years old so you should be on your 2nd set of O2 sensors, for sure

TPS is the throttle position sensor, it tells computer what driver wants to do, also used to calculate LOAD on the engine
TPS is a 5volt sensor, with foot off the gas pedal computer should see just under 1 volt, 0.79v to 0.99v is spec
With gas pedal to the floor, computer should see 4.5v to 4.6v
With 5volt range 1 volt is 20%, and wide open is 90%, so never 0% or 100%
At idle 17%(just under 1v) would be correct


Now the numbers
O2 sensor generate their own voltage, 0.1v to 0.9v so under 1volt
0.1v is high oxygen, also called Lean
0.9v is low oxygen, also called Rich

Upstream O2s change voltages very fast, but the computer tries to keep them in the 0.3v to 0.5v range, by adjusting STFT
Downstream O2 sensor voltage is pretty stable because the Cat Converters SHOULD burn up most of the oxygen when it burns up pollutants, that's the point of the Converters
Downstream O2 should be in the 0.7v to 0.8v range, they will drop down now and then as the computer FEEDS the Cats extra gasoline to keep them HOT

If you don't know how old your O2 sensor are then I would change them now, because ALL the fuel trim data is based on feedback from the O2 sensors, and if they are wrong then you will be chasing your tail looking for vacuum leaks, EGR leaks, that don't exist or failing injectors or fuel pump that are not failing

 

Thanks very much Ron! That was very helpful.

I didn't have internet last night, so before I saw this I was checking, and actually found a large vacuum leak - a hose connecting the air intake to the top of the right side of the engine (near the oil fill cap) had fallen completely off, so I put that back in. Given what you said, I'll definitely order new O2 sensors and switch those out, and see what happens - I don't think they've ever been changed. I'll get underneath to check for sure, but I take it that I'll need four new O2 sensors?

Thanks again!

 

Most of what I saw says there are 4 O2 sensors on a 2005 3.0l Ranger

 

Thanks Ron! That helps. I'll order those soon, might as well start saving fuel haha.