Chrysler Repair: oxygen sensor, scanner instructions, oxygen sensor

Question
check engine came on, had it scanned, said problem was front o.s. R/Red and cleared codes. Light came back on stating this time it was the rear oxygen sensor. so we replaced the rear als. now the check engine light is back on and it states that there is a porblem with the front...now what?
1998 chrysler sabre

Answer
Hi Dave,
I would re-check that the code numbers are correctly listed on your scanner instructions, if they just readout out as numbers. Try:    www.allpar.com/fix/codes.html
If that doesn't explain it, then I would suspect a "common mode" reason for both of the sensors to appear to cause a problem: for example the voltage supply for the sensor heaters (dark green/black) or the ground wire (black) for the heaters of the sensors are poorly connected or severed for example. So see if the pins for those colored wires have a voltage on them/are grounded, respectively.  It might also be the case that you need to run the engine for a while for the internal build up of crud near the sensors to burn off? I haven't had experience with a problem like you have described, but these are my thoughts.
Let me know what you learn.
Roland