tjwalker

Boy, it would be very unusual for the engine to code for a HEATER CIRCUIT problem on both sensors at the same time. It would be extremely unlikely that both sensors failed at exactly the same time. That being said, I do agree that NTK is the way to go with oxygen sensors and getting new ones in there is a good idea.

I know you said you checked the fuses, but did you check the 15 amp mini fuses in the PDC with a METER? There is a 15 amp mini fuse in the power distribution center under the hood that controls the oxygen sensor heater circuit. It is not that unusual to have that fuse blow; I have seen it a few times on 97-01 XJs Just want to be sure that you are not chasing your tail on this.

If that fuse is verified with a meter (or try swapping in another one), my gut instinct is that you have an issue with that oxygen sensor heater CIRCUIT (ie: wiring)

Chabada15

I don't understand why I would check the fuse with a meter, if the fuse is good then it conducts and carrys voltage, if its bad then it does not correct? If I'm checking with a meter what voltage am I looking for? But yes I did check all of those fuses in the box under the hood (I did mention this above) I've actually been checking them frequently hoping that one will pop and I can be done with this, but I should be putting the new O2s in tonight ill post up with results...

SeriousOffroad

The fuse you need to check IS NOT in the PDC under the hood. As I stated in my previous post, it's in the Junction Box. That's in the rig, passenger side footwell.

tjwalker

Yes, there is a fuse for the oxygen sensor in the junction box. Slot 10 I believe.

But the fuse for the oxygen sensor HEATER circuit is located in the power distribution center under the hood. I can't recall the exact location; somewhere between 17 and 24 I think. But it definitely is a mini 15 amp fuse.

BOTH of these fuses should be verified.

When you test a fuse with a meter, you don't test for voltage. You simply remove the fuse, put a meter lead on each end and test them for continuity (resistance) to be sure they aren't blown. Visual check is good, meter check is better and definitive. If you don't have a meter, just swap the oxygen sensor 15 amp mini fuse with another 15 amp mini fuse.

SeriousOffroad

D'Oh!!

My mistake.....
Fuse #23 in the PDC (15 amp) is the one that protects the Downstream O2 sensors (heater circuit)
Power is provided by the ASD Relay, thru the 15 fuse, then down to the splice before going to each sensor.

Chabada15

i can solve this quickly and easily, since there is not a fuse box or junction box on the passenger side...i have a 96, the inside fuse box is on the drivers side, and all of those fuses are all good, i checked the mini fuses in the junction box under the hood with a multimeter for continuety and the fuses are good, im going to install the sensors now and hope that it kills the light

Chabada15

ok cleared the codes, and let the truck idle for 15 minutes, took it for a 15min drive no light, seems like the mopar parts did the trick, will keep updated

Chabada15

Opened my mouth too soon, driving to work I got the check engine light, only 2 codes now though, none pending, both sensors for HEATER CIRCUIT MALFUNCTION!!!! I checked all the dam fuses, I'm gunna check all of them again just to be redundant but I'm not going to lie this is driving me up a wall, I hate that light, I have the haynes manual so I think I have the schematic for the heater circuit...again mine is a 96 anyone got anything?

tjwalker

Swap the 15 amp mini fuse for that circuit with another to be sure it isn't involved.

If/when a fuse issue is conclusively ruled out, I think that you most likely a wiring problem with that oxygen sensor heater circuit.

hankthetank

put your leads on either side of the fuse terminals and measure resistance...low/no resistance could mean a short i guess.

Chabada15

the fuse is most definitely ruled out

thank you will do

does anyone know if there is a relay that turns the heater circuit on or off? if there is its location?

hankthetank

right hand shock tower i think, you can test the heater on the sensor too, on a and b it should be 5 to 7 ohms. either way, infinite resistance means its done.

Chabada15

if i check the wire for the heating circuit at the O2 sensor for continuity i should get something right? if not at that point im going to assume its the ECM

is there a relay for the heater circuit thats also unmarked?

hankthetank

...

HiPoint

Do you have power to your fuse for the heater circuit? If so, chase down the wiring from the fuse to the splice in the circuit that goes to both O2 sensors. Those splices in the wiring loom will corrode and its an easy fix with a heat shrink connector (depending on where its at).