Hey guys. Its been awhile since my last post, but I've been out of town. I recently learned that my rear main seal was leaking. I had not driven the truck in over a year, but the maintenance has been by the book up till then. I pulled the tranny to change the seal ( $20 seal and my shop quoted me $550), and a day later I pulled P0156. I know this is the drivers side aft o2 sensor. I recently passed an emission test and had no pending codes before I pulled the gearbox. I carefully inspected all the wire looms and connectors, but I think I may have caused this fault during the tranny job due. Any ideas. Thanks. 1998 4.2L V6 4r70 tranny 210,000 miles

 

p0156 is a signal circuit code so you're going to want to go to the connector and make sure none of the pins are pulled or and the connector is pushed in all the way then check the harness to see if it's rubbed or pinched anywhere.

 

I'll have to check that out. I figure it will be something simple. I know it is not a bad sensor though and that's frustrating. Thanks

 

I cleaned all electrical connections and checked the sensor wires for breaks. Found nothing obvious and problem persists. Checked sensor with multi-meter and manual and found a high resistance at idle. Swapped the drivers and passengers sensor aft of the cat and drove the truck until the code popped again. This time it through the code for the other bank. Replaced bad o2 sensor. Messing around with the xmsn, I must have bumped the exhaust hard enough to kill the sensor.

 

Yeah that's kinda weird, At least you got it figured out. Does the porcelain look cracked or anything?

 

Not at all. It looks used and that's about it. I compared the resistance readings at idle with may Haynes manual and it read low. That's why I swapped the 2 back sensors. When the code swapped locations I was satisfied enough to spend the $60. I bought a Bosch replacement. I don't believe in coincidences, but I guess I just experienced one. Cheers.