Quick question. Long history of issues with my recently purchased 2000 Cherokee 4.0 A/T.

First I Had no injector pulse. Replaced PCM and injector pigtails and C2 pcm connector. Actually ran better but then had an intermittent misfire on cyl 4. Replaced coil pack and plugs. Runs better. But now I have a P0171 fuel system Lean bank 1. Was getting ready to order new o2 sensors and a TPS but I thought I would check and see if the 02 heater circuit was functioning.

I found the entire o2 sensor harness was melted together. Patched it back up with good heat shrink. 02 sensor is reading as expected but I have zero voltage on any of the 4 pins on the vehicle side of the upstream o2 sensor harness. Should there be a constant 12V with the key on to the heater circuit at this harness? Would a non functioning o2 sensor heater cause improper metering of the exhaust air/fuel ratio and throw a P0171 and poor idle/ bucking and running rich?

thanks for any help.

edited to add I have checked the o2 heater fuse as well as the relay. When removing the relay with key on the relay clicks when you put it back in so I know it’s sending voltage somewhere.

 

If the heater in the o2 sensor was bad you would get a code for that . If you o2 sensor are old or if they were cheap ones I would change them , just the up stream ones , the ones before the cats .