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I’ve finally have the time to replace the downstream sensors on my ‘01 XK8. I don’t know if it’s going to be what resets the cat monitor but we’ll see. Is it recommended to disconnect the battery or can I just unplug the old ones and plug in the new ones?
Oh, I forgot to ask if anyone knows why the Denso upstream sensors are so expensive? I’m showing a part number 234-9016 with
a price of almost $300 each!
Best price I’m finding is Rock Auto $217. I’m going to put the downstream ones in today and see what happens. I’ll try the drive cycle that is supposed to reset the CAT monitor AGAIN and see what it does.
I hesitate to post and find out I've made a tragic error - but i replaced my 03' XKR downstream sensor a few months ago with 234-4798 which is what the Denso site said fit our car. It is $60-$80 depending on where you shop.
It made the lights go away and car seems to be running really well. Hopefully no one will follow up with something terrible I've overlooked...
Oh, nm... I misread you were talking about the upstreams being $$$.
Last edited by chilly; Apr 26, 2025 at 10:04 AM.
Reason: misread
I hesitate to post and find out I've made a tragic error - but i replaced my 03' XKR downstream sensor a few months ago with 234-4798 which is what the Denso site said fit our car. It is $60-$80 depending on where you shop.
It made the lights go away and car seems to be running really well. Hopefully no one will follow up with something terrible I've overlooked...
Oh, nm... I misread you were talking about the upstreams being $$$.
no worries Chilly. It’s early here and I sometimes have trouble reading this early in the morning too LOL.
That’s about what I paid for the downstream ones too. Now once I finish this pot of coffee I’ll get the car up on the jack stands and get to wrenching.
Oh, I forgot to ask if anyone knows why the Denso upstream sensors are so expensive? I’m showing a part number 234-9016 with
a price of almost $300 each!
the upstreams are a wideband sensor. they're also a bitch to get at. fortunately, you are doing the downstream which is less painful.
top tip tho, when you unplug the old one, tie a string to it, that way when you pull it out it'll leave a string you can pull the new sensor wire through with.
the upstreams are a wideband sensor. they're also a bitch to get at. fortunately, you are doing the downstream which is less painful.
top tip tho, when you unplug the old one, tie a string to it, that way when you pull it out it'll leave a string you can pull the new sensor wire through with.
Hi Throwback,
Thank you, good idea. Any thoughts on disconnecting the battery?
Best price I’m finding is Rock Auto $217. I’m going to put the downstream ones in today and see what happens. I’ll try the drive cycle that is supposed to reset the CAT monitor AGAIN and see what it does.
Don't hold your breath. I'm putting mine up for sale shortly. I think my cats are shot and no amount of futzing has made the cat monitor set. I'm not throwing another grand at this car for new cats in order to drive a ticking time bomb that *might* fetch $3K if running properly.
the upstreams are a wideband sensor. they're also a bitch to get at. fortunately, you are doing the downstream which is less painful. Well, several hours later and I've managed to disconnect the wire connector, hang it by a string, and slide both of the sensor sockets onto the sensor (passenger side LHD) and then go to the store to buy more 1/2" extensions. However, as of a few minutes ago I still can not get any combination of regular extensions, swivel extension and swivel sockets onto the sensor to the point where I can turn it. I've got the sensor soaking in WD40 and Kroil now.
top tip tho, when you unplug the old one, tie a string to it, that way when you pull it out it'll leave a string you can pull the new sensor wire through with.
I'm completely convinced the designers who are at the top of the food chain are not the ones who make the cars look great or the ones who make it comfortable or put in all the fancy stuff, but the ones who design parts that need to be replaced and figure out how to put them in the most inaccessible place on the car. I know these things are supposed to come out without removing the cats but I'm not sure how this is done. I can see the bolts on the bottom that have to be removed to get the cat out but can't quite see the top ones.
OK, here are the photos of what I think are the bolts that have to be removed to get the whole CAT out. Could someone let me know if I've found them all or if there's some magical, not easily seen or gotten to bolt that I'm missing.
This is one of the upper bolts This is the other upper bolt. This is the bracket holding the CAT to the bolck. There are also 2 other bolts holding the bracket to the block that may have to come out. I'm thinking these 2 bolts have to come off to lower the exhaust pipes enough so the CAT can be dropped This is the bolt that holds it to the exhaust pipe
I've tried from a couple different angles but I can't get any of the extensions into a position where I can put the breaker bar on them to get this thing off.
Looks like it's unbolting the Cat and the whole thing is going to come off. Grrrrrrrrrrrrrrrrrrrrrrrrrrrrrr
Aren't you just replacing the downstream sensors? If so, you just need a really long extension and a crow-foot O2 sensor socket. You come at them from back near the end of the trans tailshaft. Push the extension up to the sensor, put the crowfoot socket onto the extension, put the socket onto the sensor, put the ratchet onto the other end of the extension and give it a mighty pull. Once the sensor is loose you can remove the socket, etc., and turn it out by hand. Assembly is the reverse.
The left side of the car is a bit more difficult than the right owing to the trans shifter connector.
That’s what I’m using. I can’t get the socket at a position where I can get the extension onto it. I’ll go back out later and try again but I’m not seeing any way to do it.
That’s what I’m using. I can’t get the socket at a position where I can get the extension onto it. I’ll go back out later and try again but I’m not seeing any way to do it.
I had a short "wobble" extension on the end of the much longer extension, which helped quite a bit. On the left side I was able to get a 7/8" wrench onto the sensor and turn it enough to get the socket onto it.
O2 sensor replacement
