Chasing a code mystery
 

Hey there..

Im pursuing the solution to p0170 and p0156 codes . My LTFT and STFT are both within range. No vacuum leaks. my 02 post cat bank 2 is reading no voltage. I have tried two new sensors. Im getting 12v power from the source connector. I am stumped and I’m down to the last few weeks to pass emissions.any help out there? Will a dealership even look at my old 2001 limited?
and can somebody tell me if the ecm is powering the sensors and where the heck it is…https://static.xx.fbcdn.net/images/e...2/16/1f923.pngthx

Is it possible there is a break in the cable that goes back to the ECM? Look for any damaged cables, pay close attention areas that can get real hot or subject to moving parts. The fact that you get voltage at the source but no reading at the ECM leads to believe this is the issue.

There is no voltage reading from the sensor, not the ECM. But there is 12 volts present at the harness connection that plugs into the sensor.bI don’t even know where the ECM is actually.


https://cimg6.ibsrv.net/gimg/mitsubi...cb8571ba6d.png
A question I have is…I know there is 12 volts power to heat the element in the 02 sensor but is there also separate power to send info from sensor back to ECM? I found this diagram from another montero owner. Any insights?

You are talking about the wire that sends data back to the ECM or maybe one of the ground wires having a break?

The 12v you are reading on the connector is the voltage to power heater element in the O2 sensor. That does not go to or from ECM. ECM reads the signal on the B pin when that goes through sensor to ground. You should read 5v to body ground on pin B when sensor is disconnected. Obviously the ground pin (A) should gave a good signal between vehicle ground and that pin.