I have searched and searched online but cannot find anyone with the same issue as me:

2000 Cherokee Sport.
It was running fine, no codes.

I changed the water pump and put the original fuel injectors back in last weekend. (It had dodge neon injectors in it for about a year).

Upon restart, I get an intermittent, cold-start, CEL. Codes are BOTH upstream and downstream O2 sensor heater circuits (says all four O2 sensors have bad heater circuits (P0135, P0141)

It is not likely that all four (or even one) of my O2 sensors magically failed while I was changing the water pump and injectors.

Checked fuses. All good. Relays appear to work. Cleaned battery terminals and made sure it has a good ground. Unplugged and re-plugged O2 sensors and other connectors in the same general area.

Clear the codes and it runs fine. But next start, or the next one, or the next one, CEL is back. ALL O2 heater circuits bad.

It seems to run fine. No sputtering. And the CEL comes on about 30 seconds after start up. Seems to be a cold start thing.

Anyone?

Please????

 

Here's your PDC fuse layout, and a pic of the entire PDC showing the relays.


Relays don't "appear to work". They work or they don't. :-)

 

Deleted post.

 

MANY, MANY Thanks to CCKen!!!

Every fuse box diagram I have seen up to this point shows a 15 Amp fuse on the back row being the O2s fuse. YOUR diagram indicates a 20 Amp fuse on the second to last row.

I ran out to the jeep just now and pulled the 20 amp and BLAMO! It was Blown!!!

I replaced it just now. (I keep a plastic box full of fuses in the PDC, under the lid...)

I didn't bother to start up the Jeep because there was OBVIOUSLY a fuse issue with the O2 Sensors. It may have popped when I disconnected and reconnected the battery during the injector swap.

NOW....the question: WHY did the fuse pop? It has never popped before. I have had the negative terminal off many times. I have replaced all four O2 sensors in the past. I have replace injectors and water pumps on this vehicle in the past. The fuse never popped before.

So I am thinking exposed wire on one of the O2 sensors or something? I mean......under normal conditions fuses don't just randomly pop.

Any suggestions?

(And THANKS AGAIN for the diagram that was different from ALL THE OTHER DIAGRAMS. Saved me some serious time.)

 

For anyone else having this issue in the future:

The 2000 and 2001 XJ has a 20 AMP FUSE in the second to last row that controls the O2 Sensor relays. NOT the 15 AMP fuse in the last row of the other Power Distribution Centers.

AND: I was getting trouble codes for ALL FOUR O2 Sensors' Heater Circuit.

AND: The Jeep seemed to be running fine. I didn't even really see a gas mileage issue. No sputtering at all (I did notice a slight sputter at idle when the engine reached temp yesterday. I nudged the pedal and it smoothed right out.

So, I had CEL and codes for all four O2 sensors heater circuit. AND the jeep ran fine. AND it has a 20 amp fuse instead of a 15 amp fuse.

Hope this helps someone else.

(Still not sure if I have a short somewhere. But I suspect the downstream sensor that has wires that can rub against the side of the oil pan. I will wrap them up with some tape and see if the fuse holds up over time.)