I'm trying to get my 2004 F-150 Heritage RWD 4.2L V6 4R70W Regular Cab back into a drivable condition, and part of that is trying to fix a P0171 code (System Too Lean Bank 1). I believe I've narrowed down the issue to the Bank 1 downstream O2 sensor reading erratic voltages while running, when compared to Bank 2 which reads smoothly. To further back this up, when I look at the sensor voltage, with the engine off (also happens when the sensor is cold), it reads 0.005V. All of the other O2 sensors read 0V like expected. I assumed that the O2 sensor was dead, so I started replacing it. I've gotten the sensor out and I'm buying a new one tomorrow, but in the process of getting it out I cut the wires so I could easily remove the supposedly "dead" sensor.

After getting the sensor out, I decided on a whim to test the voltage once more and see if it was reading 0V like it should. Despite the fact that the sensor is completely disconnected, I'm still seeing 0.005V. And I know I'm not looking at the wrong sensor voltages because I can see correctl voltage reading from the other downstream sensor (Bank 2).

I'm at a loss for what to do now, and I'm a bit afraid that there could possibly be a problem with the PCM. The sensor I took out might not have been dead, and it didn't look too bad, just had a some carbon buildup. Any suggestions on what to do next?


(I'm reading the voltages with my Bluedriver OBD2 scanner. I'll also post an update when I put in the new O2 sensor tomorrow)

 

Get a 40 dollar can tool like a konwei

Watch the front O2 sensors switch (above and below).5 volts up to 1 volt
Report back those results
Also check the fuel trims for the lean code
Post exactly what you are driving
A 04 heritage with a 4.2 and one with a 5.4 are completely different animals
If a 4.2 and a code 171 your "isolator bolts" need to be replaced
Those are just the lower intake bolts with the rubber washers on them someone decided to call "isolator bolts"

 

You realize that the difference between 0 (zero) and .005 volts is only 5 millivolts? The difference is irrelevant in the larger scheme of things so don't fixate on it.

 

Mistake