2005 Jeep Liberty 3.7L P0137 & P 0157

I just changed the transmission on my 2005 Liberty, and since then am getting a P0137 and p0157 code. I checked the wiring, with the sensors unplugged, it's showing 1.25 on each, plugged in, shows the same on all sensors with key on ignition off. As soon as the engine starts, both front sensors oscillate as normal, and the rears do for maybe five minutes then drop to zero volts on both. I do not know if these sensors are OEM or not, they look to be Bausch. Could me removing the exhaust and maybe getting banged around a bit have caused them to go bad? I just got a Hantek scope, but haven't used it yet and am pretty green using a scope. Thanks for any and all input.

the post 02's have four wires... a power and ground for the heater and a signal and ground for the sensor. on which wire/s are you getting the 1.25v.

The 1.25 is on the signal wire showing on the scan tool. It oscilates Norman until warm, then flatlines.

Start it and wait for one or both of the rear o2`s to flat-line @ the 0 volt mark, then dis-connect 1 or both of them and see if the o2 data pid for them jumps back up to the 1.25 volts. I believe this would be a good directional test and could possibly prove the o2 sensors are @ fault. Good Luck.

ScannerDanner actually has a great free youtube video talking about this test method since it appears your chrysler uses a bias voltage.

skip to about the fifteen minute mark in the video
www.youtube.com/results?search_query=scanner+danner+o2+sensor

I tested as you said and it does jump back to 1.25v. So I know that the wiring is fine, As info, the fronts are working fine and total fuel trim on each bank is under +4. There seems to be good exhaust flow coming from the tail pipe and no exhaust leaks. I leaning towards the sensors. Would them banging around during the exhaust removal and install cause them to go bad? Like I said earlier, when cold starting they are osculating along with the fronts. It doesn't take long for them to go to zero though, maybe 1 minute or so. I also checked the heaters and there is good current running through them.

Thanks for the input.

downstream 02 sensor voltage should oscillate 2.5 to 3.5v. voltage on the ground should be 2.5v.

bosch sensors used upstream on chryslers are known for problems... could be same problem when used downstream.

If the 02's were working fine prior to the trans repair and you have no wiring damage, then I would suspect the 02 have gone bad.

Yes, you can damage the 02 by contamination or mis handling.

I have replaced the downstream sensors and have no more C.E.L. That did the trick. Now my wife tells me that it smells like it is burning rich and I kind of agree with her. The fuel trims are spot on + or - 6 total fuel trim. I'm thinking about changing the upstream sensors to also be OEM. Does anyone think that it is a good idea even with good fuel trims? Any other suggestions?

neg fuel trims suggest a rich condition... as I mentioned before anything other than OEM 02's for Chrysler/Jeep cause problems. Did you clear code after fix?

I did reset the code after fix and monitored the fuel trims and they look fine. averaging around zero, of course some + and some -, but all within ten percent overall. I have seen that aftermarket on Chrysler vehicles will cause issues and I don't know what this has in it. If the current sensors are aftermarket, would they cause lean or rich trims? I'm not sure. With my mindset, if the sensors are inaccurate, I would think the the trims would be off.

the aftermarkets have a problem with the heater circuit and keeping the 02 at operating temp... with the trims where they are should not be issue but you have fuel smell. Is the smell in the engine bay or out the tailpipe?