1998 Chev Tahoe K1500 5.7L O2 Sensor = 0mV

[CalRewireMatt]

I have a 98 Tahoe 5.7, 4l60e 4wd in here with a very odd issue.

The truck came in because the b2s1o2 sensor connector melted. We cut on a new connector and put in a new sensor. While testing it out we found something odd. With Key on engine off, all sensors start at 450 mv. As the heaters warm up all the unaffected sensors maintain that approximate voltage but the sensor we fixed will drop off to 0 mv in the span of 10-15 sec. We installed a different sensor and that did not rectify the issue. Running the truck also didnt change anything.

Noting that it seemed to be related to the heater coming on, I deppined the ignition circuit from the o2 connector and retried it. This time the sensor acting like all the others and while being a bit slow to start switching, after a minute or so the o2 was switching away happy as can be. I made sure we are hooked up properly for pin location, did continuity checks of both circuits going back to the pcm, power and ground as well as checking any shorts to ground, power or across each other. No issues were found. I opened the PCM up and didnt find a failed component visually so Ill assume its good for the time being.

I used p0151 as a flow chart to test from and so far everything falls in line. Considering the heater circuit is electrically seperate from the sensor circuit I wonder why the heater is affecting it and why it does it regardless of the part installed (two new o2s and the left front being switched all same issue)

I dont want to condemn the PCM yet so wanted to ask if any of you have seen a problem like this and what you did to repair it.

[steven kiser]

As a rule when i find a melted connector or in line plug melted it's a result of a bad connection. This causes the circuit to over heat and as we all know will not blow a fuse but will cause a fire. I feel the p.c.m. is junk and needs to be replaced. If you check the spark plugs on that bank you may find them a bit fouled and need replacement. For some reason i see that a bit.

[jbadenoch]

I'm in agreement with steve. If the connection was melted then it most assuredly shorted the wires and probably that circuit to pcm. Keep us posted