98 ranger 3.0 xlt. Threw a P0171 code. OBD2 showed 0 volts at all O2 sensors. All fuses ok. Removed PCM and want to test. My question: if i test the prong from the pcm for the O2 sensor signal wire with the prong to the signal return wire, should it read 0.0 resistance? These 2 prongs on my pcm are # 35 and 91

 

O2 sensors have 4 wires
2 for a built in heater
Key on 12v, in 1998, that is fuse 13 in Engine Bay fuse box
Then a ground for the heater that goes to the computer, pins 93, 94, and 95 on PCM, one ground for each O2 heater

Other 2 wires on an O2 are for the sensor part and will have 0volts until O2 heats up, O2 sensors generate their own voltage but only when heated above 600degF, so give engine 5mins of run time to heat O2s up

Orange wire is shared on each O2(like the 12v wire) it will go to pin 91 on PCM, its the Common Reference "ground", its also connected to the other "sensors" on the engine but uses a grey/red wire, so all sensors are connected to pin 91, not just O2s
The voltage from each O2 sensor part goes to PCM pins 35, 60 and 87

P0171 System too Lean (Bank 1)
That should be 91 and 60
35 would be downstream O2 I think

Never test ohms on sensor part of O2

But also never heard of all 3 O2s showing 0 volts after warm up

 

TY Ron.
i have found out by testing that pin 60 goes to pre cat O2 sensor b1 (on passenger side), and that 35 pin goes to both pre cat O2 sensor b2 and the post cat sensor..
i found a break in continuity between pre cat O2 sensor b2 and pin 35. Im not sure if this would cause all of my O2 sensors to show mo voltage but i will patch this apparent short tomorrow and post an update. Thanks again.

 

That is odd, pins 35, 60 and 87 wires should have no connection outside the PCM

Not for sure accurate but best I have for engine wiring in 1998 3.0l

 

Im going off this

 

And when i tested pin 35 to signal wire from post cat O2 sensor o found continuity there

 

Thank you Ron for the diagrams but they are incorrect for mt truck. Not sure why this is because all 98 boxes should be the same. But your diagram clearly shows pins 20, 33 and 34 being used and these are all empty slots on my pcm. I appreciate the effort.

 

Did you ever find out what the issue was? I am having the same issue and can't figure it out!!!! Thanks in advance.