I just replaced my first set at 135k. Actually, the check engine light came on around 120k, but only in cold weather. The light went off and never came on once the weather got warmer, so I put it off till this winter when the light came on again. (It was the same sensor code both times.)
Unfortuately I have the Overly Redundant model, so I have four sensors, each costing around $70.
Both upstream sensors came loose easy with a 7/8" wrench. If you're doing both at the same time, it's probably easier just to take off both the air-filter-box lid and resonator so you can work the wrench from topside easily. I had to take the resonator off just to get to the connector for the rear sensor which they placed way in the back of the engine, a place that's not as easy to reach as it was back with the original Cherokee.
Upstream front: 56028995AA
Upstream rear: 56028997AA
Both downstream sensors were hard to remove. Use some WD40 and get a 7/8" flare-wrench socket. The deepwell type sensor socket wont work on the rear sensor. The deepwell type tend to slip and round off the sensor nut anyway.
It's possible to do these without jacking up the vehicle, but it's a lot harder. Stock ground clearance really sucks.
Downstream front:56028994AA
The downstream rear sensor is the hardest one. The fact that it's buried in behind the exhaust pipes is bad enough, but there's a stupid heat sheild holding the sensor wire to the oil pan.
The heat sheild is basically a gasket that's held in place by little snap washers that are slid up over two bolts that stick out of the bottom of the edge of the oil pan. You have to find a way to get your hands up in there, pop those stupid things off, and then pry the gasket down off the bolts.
Since the sensor wire has to be routed through that spot, which is right next to one of catalytic converters, it's probably best to get that stupid thing off in one piece and get it back on like it was. The wires would probably melt in that spot if left unprotected, and there's no other place to run them.
There was a flimsy foil tag on the sheild that I tore all to crap. It was stamped with a part number, so here it is if you need a new heat sheild: 56041675AA
Now, there's the issue of the proper part number for this sensor. wjjeeps.com says it's 05139021AA, so I ordered that from the cheapest sourse I could find: ebay. The box said 1-05139021AA, but the enclosed sensor was stamped with 56044598AA.
Several internet sites said that this sensor was indeed the downstream rear sensor for an 2004 4.0. I called the parts department of my local dealership, and they said that *1AA was the right one, and that *8AA wasn't in his records.
All four sensors that I bought were Mopar brand, and all four sensors were stamped with NTK's logo.
So upon pulling that sensor from my vehicle, I found that it was also a 56044598AA, which matched the sensor that came in the box.
I'm not sure what the deal is with the part numbers for that last sensor, but it seems that it doesn't matter if you buy 05139021AA or 56044598AA. Either way you'll get a 56044598AA in the box.
Unfortuately I have the Overly Redundant model, so I have four sensors, each costing around $70.
Both upstream sensors came loose easy with a 7/8" wrench. If you're doing both at the same time, it's probably easier just to take off both the air-filter-box lid and resonator so you can work the wrench from topside easily. I had to take the resonator off just to get to the connector for the rear sensor which they placed way in the back of the engine, a place that's not as easy to reach as it was back with the original Cherokee.
Upstream front: 56028995AA
Upstream rear: 56028997AA
Both downstream sensors were hard to remove. Use some WD40 and get a 7/8" flare-wrench socket. The deepwell type sensor socket wont work on the rear sensor. The deepwell type tend to slip and round off the sensor nut anyway.
It's possible to do these without jacking up the vehicle, but it's a lot harder. Stock ground clearance really sucks.
Downstream front:56028994AA
The downstream rear sensor is the hardest one. The fact that it's buried in behind the exhaust pipes is bad enough, but there's a stupid heat sheild holding the sensor wire to the oil pan.
The heat sheild is basically a gasket that's held in place by little snap washers that are slid up over two bolts that stick out of the bottom of the edge of the oil pan. You have to find a way to get your hands up in there, pop those stupid things off, and then pry the gasket down off the bolts.
Since the sensor wire has to be routed through that spot, which is right next to one of catalytic converters, it's probably best to get that stupid thing off in one piece and get it back on like it was. The wires would probably melt in that spot if left unprotected, and there's no other place to run them.
There was a flimsy foil tag on the sheild that I tore all to crap. It was stamped with a part number, so here it is if you need a new heat sheild: 56041675AA
Now, there's the issue of the proper part number for this sensor. wjjeeps.com says it's 05139021AA, so I ordered that from the cheapest sourse I could find: ebay. The box said 1-05139021AA, but the enclosed sensor was stamped with 56044598AA.
Several internet sites said that this sensor was indeed the downstream rear sensor for an 2004 4.0. I called the parts department of my local dealership, and they said that *1AA was the right one, and that *8AA wasn't in his records.
All four sensors that I bought were Mopar brand, and all four sensors were stamped with NTK's logo.
So upon pulling that sensor from my vehicle, I found that it was also a 56044598AA, which matched the sensor that came in the box.
I'm not sure what the deal is with the part numbers for that last sensor, but it seems that it doesn't matter if you buy 05139021AA or 56044598AA. Either way you'll get a 56044598AA in the box.
