Been having a check engine light on for codes 135,141,155 and 174. Basically, O2 Sensor and Lean codes. Been checking everything I know to check including looking for open or short in the O2 circuit. A visual check has come up empty. Thought about trying out a Power Probe ECT 3000 to attempt to find the open circuit. Has anyone tried this tool or one like it? If I can't find the open circuit, then maybe it is an ECM problem.

 

So the codes give you a lean condition and heater circuit error in the bank two upstream, and the downstream sensor. You should be able to use a multimeter to test the sensors, and make sure the ECU is sending the heater signal.
https://www.f150forum.com/f93/oxygen...-codes-565680/ This recent thread should be relevant to you.

 

There is a fuse that powers both heater circuits
If your scan tool will read PIDS, you can check all 4 HEGO pids
Watch them switch and see how long it takes them to start switching from a cold start
That's what the heaters are for, they want closed loop operation quicker
I'd check the fuse and verify power, then check the resistance of the heater wires in the sensor
Replace the HEGOs if the heater resistance is open circuit

Use the pin numbers, the wire colors change over the years. On most of the new sensors, the heater wires are white. This diagram is for an old Bronco

 

I have tested the O2 sensors per the 1996 Ford Powertrain Control/Emissions Diagnosis OBD2 service manual along with the 1996 Ford Electrical and Vacuum Troubleshooting Manual and everything else I could check without special tools ( breakout box, ect ) The original O2 sensors checked out ok but I replaced them anyway because they were 29 years old. I currently have pulled the EEC-V Electrical Engine Control ( computer ) and found the pins clean and opened the computer up and found no obvious damage. I must be missing something? My OBD2 reader is a pretty basic one so I am unable to read live data. Maybe it is time to upgrade. And the fuse was one of the first things I checked, power to both sides of the fuse.

 

How closely did you look at the traces on the PCM circuit board. This thread has pictures of trace damage. It's a different year and PCM than yours, but a good example of trace damage: https://www.vintage-mustang.com/thre...in-46.1196162/
The other thing you could do is to clean all the ground points, that may affect the PCM.
Off the top of my head those are; behind the driver's side kick panel, near the emergency brake pedal; on the passenger's side fender, near the battery; on the driver's side fender, near the hood hinge; on the driver's side of the upper radiator support, near the windshield washer bottle; and the main ground cable, from the battery negative terminal, to the lower face of the engine block, on the passenger's side.

 

EEC looked good and all grounds were removed and cleaned and reinstalled. I will figure this out with this sites help hopefully.

 

So, I have replaced all 3 O2 sensors even though they checked out ok cause they were 29 years old. Checked the 15 amp fuse and removed and cleaned the grounds. Checked the fuel pressure which was a little low at idle (28 psi) and jumped up to 36 psi when I disconnected the vacuum line from the fuel pressure regulator. Did a smoke test for vacuum and no leaks found. Cleaned the Mass Airflow sensor and checked the Air filter. The fuel filter only has a few thousand miles on it. Pulled the EEC and all the pins looked good and were cleaned with electrical contact spray. Opened up the EEC and all looked good. The truck runs and drives good just has that check engine light that won't go away. I have never taken my truck to a mechanic but I am running out of options. I like to do the work on my truck but I might need some more help on this one.

 

Have you watched the O2 sensors switch? With your scan tool?
I'd be looking into the lean code P0174 next, doing some of the pinpoint tests in the PCED

 

What do you mean by O2 sensors switching? What is the PCED? Is that the EEC or computer? Still trying to learn this OBD2 language.

 

O2 sensor switching
A working sensor in a working motor with good injectors etc.
Will switch from zero volts to 1 volt (above and below 1/2 volt) rapidly
They figure a stoichiometric ratio of 14.7:1 ratio of fuel to air is the correct air fuel ratio for both emissions and fuel economy
They cannot just program in 14.7 if you are up there hitting the gas and coasting and such
So, they have the O2 sensor switch above and below 1/2 volt where 1/2 volt is the 14.7 ratio (1/2 volt is the target ratio)
That way as the volts drop, and the mixture goes lean, the processor adds more fuel until the mixture goes rich
This happens over and over quick, The O2 sensor will read say .17 and then .79
Then quickly read something else like .30 and .57, and then .49 and .76
Over and over, they switch (above and below 1/2 volt)
If one gets stuck rich or lean, it might be reading correctly and actually reading a lean or rich condition
So, you want to watch those O2 sensors switch, if any problem occurs just about every time
First thing I do is watch the O2's switch and check the fuel trims
Got all that?