My sister's truck. The heads started leaking water, and only water was put back in. Last winter, the freeze plugs burst out of it. So, I pulled the motor, got new heads, had the block checked, cleaned and honed; re-ring kit, new gaskets, the works. Put it back in, and now it won't pass inspection. My small code scanner said it was the rear o2 sensor, so I replaced it. Still the same code. I replaced the tranny harness. Still there. So I bought an OBDII to USB cable and a diagnostic program for my laptop. It is showing closed loop, running off the o2 sensors, but in the sensor window, no voltage is generated from any of the three. Where do I go from here?

 

Also, the fuel trims were 100% across the board....

 

My suggestion is to insure the engine coolant temperature sensor plug is clean and plug in completely, the computer reads the temperature sensor before determining the function of the O2 sensor. If this passes inspection check for a missing, lose or dirty ground.

Hope this helps

 

Thanks for the input; however, the coolant temp is 190 degrees and I even ran jumpers from the battery ground post to the sensors. Any other ideas?

 

Do you have a DVOM to check each O2 sensor individually ? You need to take one step at a time. Let us know what readings you get with a DVOM from each sensor. We can go from there.

 

Other than checking the continuity of the wires in the engine compartment wiring harness i am clueless, sorry. I will see if I can find a wiring diagram around here somewhere, what is the engine size?

 

4.0 OHV, VIN X. I tried backprobing each sensor with an analog voltmeter, but got nothing. I thought maybe it wasn't sensitive enough

 

You should at least be seeing 12v on the 02 connectors (LB/O wire) for heater control. although the PCM controls ground/function, if no volltage present there, look first at the power distribution box fuse postion 13 15amp fuse for open,,, and check for power distribution there..

Are you seeing a voltage on the ECT connector (GY/R)

 

Still testing.... By the way, how much voltage should be on the heater OPPOSITE the light blue/orange wire (the one going back to the PCM?) I'm getting right at 12 volts (I think, wow is it late)

 

One more thing: there is 200k ohms of resistance between the orange ground wire and the negative battery post. Is this right? Where is this ground so I can clean it if it's not?