I replaced both the upstream and downstream O2 sensors on my Jeep today the rear one had been damaged by the driveshaft and the front one couldn't handle the load so both got replaced both of my O2 sensor heater codes are gone but the codes themselves are there. The Jeep is running normally again where as it was running like crap before (as you would expect from s car with no O2 sensors). But the codes are there... It seems they are working so I'm just confused. Attached are before and Afters with the codes.

It's a 98 xj

 

Good problem description. That's the right way to post a question on a forum.

Okay, let's start by clearing up a misconception. The downstream O2 doesn't in any way share the "load" with the upstream. They have two completely different functions. You could remove the downstream and weld the hole closed and it will have zero effect on your upstream sensor.


I'm not sure on those codes, but they may need to be manually cleared. Not all codes go away when the problem is fixed. Have you tried that? Have you reset your PCM?

Also, have you checked the heater fuse? It's in the PDC. 15 amp, IIRC.

 

Mark,
It's my understanding that if the info from those two sensors don't fall within spec of each other it will trip a code but maybe or maybe not the CEL. If so then there would be a relationship between the two. Right?

 

Read the link. The PCM only uses the rear sensor to determine if the cat is bad. It has nothing to do with 'sharing' any 'load' and nothing to do with how the engine runs. Cut the wires to the rear sensor and your engine will never know the difference.

 

Found my culprit .this little turd. Thanks guys!
Anyone know what these other 15a fuses do? I bought a 6 pack and did them all

 

There ya go!

 

A good while back I found out I had o2 sensor issues. I remember reading something about there being a relationship between the two. It's the reason I replaced both at the same time.

Upstream:
The upstream oxygen sensor is located before the catalytic converter. This measures the level of pollutants coming directly from the engine. It also senses any raw, unburned fuel coming from the combustion chambers.

Downstream:
The downstream oxygen sensor is located directly after the catalytic converter. This sensor measures the pollutants making it through the converter and out of the tailpipe. The data from this sensor is compared to that of the upstream sensor. If the data between the two sensors becomes more similar, the vehicle's computer may trigger a catalyst inefficiency check engine code, which turns on the Check Engine light.