I have had a CEL on and showing a 1647 code indicating a problem with the bank B upstream O2 sensor. The car has been running very sluggish since this code appeared - so much so that I have been avoiding interstate driving altogether.

Thanks to this forum, I found that I could buy a replacement sensor on Amazon for just under $60 so I decided to change them both. The direct fit replacement of quality is the Bosch 15627 and the bill for two with shipping came to less than $125. The only other costs I incurred was an offset sensor wrench (pic attached) from Harbor Freight for $7 and a $15 gallon of antifreeze to top up after the job. I started at 7 this morning and the job took roughly 2 hours. Of that time, 80% was the B bank, where I started.

First, I disconnected the battery negative. It has been written that one needn't remove the coolant tank, but I did remove the clamped lower hoses and the low coolant sensor connector to pull it out of the way, leaving only the norma connectors attached. That is why I needed some coolant afterward. I ended up pulling other hoses related to the heater as well, just to get a clear shot at the heat shield over the B sensor. Removing this shield requires removing 3 small torx screws, and then under that there is a bracket that I opted to remove to clear the way to the sensor. This required removing three of the exhaust downpipe to catalytic converter nuts. With those off you can spin the heat shield bracket out of the way.

At this point I was looking at the sensor. There is very little room to get a tool on it. You can get a 7/8 or 22mm open end on it, but there is no room to apply force. The sensor wrench, however, was perfect. I could slip it over the wires onto the sensor and then get a 3/8 ratchet handle into it. This allowed me to ratchet into a position where I could turn the sensor maybe 1/10 of a turn before hitting something with the handle. But that was enough to get it loose. It was not extremely tight, but I had to extend my handle with a piece of pipe to get leverage in the small space. I used no PB blaster, heat, or hammers (although I had all 3 standing by) and worked with the engine cold.

I almost bought a 3/8 ratcheting breaker bar at Harbor Freight for $18 and it would have been just perfect paired with the sensor wrench - I recommend that, but my method worked fine. Even if you are lucky like me and the sensor isn't stuck like hell, you will need more than a short ratchet handle.

The new sensor went in easy and came with anti-sieze compound preapplied. I would recommend letting the wire and connector hang down below the sensor so that you don't kink or stress them when tightening the sensor down. The wire then easily routes up to where it needs to go afterward.

After replacing the heat shield, and refitting the hoses and coolant tank on the B side, the A side was a walk in the park, requiring only the removal of the MAF sensor connector, breather norma fitting, and lifting the air pipe away from the throttle body and air filter box. With that pipe off, the A side sensor is in the open and, using the same tools, easy to remove and replace.

Finally, I did a hard reboot before reconnecting the battery and cleared the CEL with my code reader. After a short bit of driving and one restart, the car runs like new again with all her normal pep and vigor. If you have the right tools and are comfortable pulling hoses and exhaust nuts, etc., it is not such a bad job. Expect to be working in a very confined space on the B side and be gentle with the old connectors and the hoses when working them out of the way.

 

Thanks for the excellent write-up!

 

Glad it worked out -- I did the same -- not much space.


I too removed the coolant tank -- emptied it with a turkey baster and closed off the hoses with "press and seal" and rubber bands after taking it off.

I left the exhaust bolts alone -- did slide the heat shield out of the way. My sensor was really stuck -- had to give it a shot of penetrating oil and an hour wait to free it up.

Its a good saturday morning project -- when you can walk away a few times!!

 

The exhaust connection is where this job can get ugly if you break a stud. I can see where you could leave the heat shield bracket in place, but I had just replaced my exhaust gaskets last year and used anti-sieze on the studs so I was confident they would come off without much of a fight.

In spite of that, I discovered the guys who repaired my transmission recently broke a stud on the drivers side leaving only three to hold the connection tight. It seems to seal fine, but seeing that broken stud was the downbeat on an otherwise smooth project. I will probably have to replace that stud at some point.

 

I found a 22mm crowsfoot attached to a torque wrench to be useful for the LH sensor.

 

interesting to hear how the O2 sensor effects performance. I wonder what the ECM decides to do when this happens, if it's vvt control, map control?
I have the same sensor throw an amber engine light after a long run on the motorway, coming off gas, it threw the code. I didn't notice any loss of performance tho' - maybe different on the S/C engine....

 

When the CEL first came on showing the 1647 code, the car still ran fine. It wasn't until I did a hard reset to see if the code persisted that the poor performance started.

 

Hi
I'm a newbie on here and have just bought a UK Jag XJ8 with the same persistent P1647 code.

Can you tell me which side of the car this sensor is on? (As if facing the car from the front looking towards the back).

What is a "crowsfoot" tool?

 

On UK cars the sensor causing the P1647 problem is on the passenger side of the vehicle, down underneath the coolant expansion tank-it's a morning's work to replace it.

If you're strapped for cash, you can buy an old sensor off ebay from the X-Type 2.5L & 3.0L V6's & these do work on the X308's.

A Crow's Foot tool means it doesn't completely encircle the bolt/nut-there's slot cut out to allow it to slip over in confined spaces & when you have a long connecting wire-as in the O2 sensors.

 

When the O2 sensors fail, the ECU uses the "Basic" fuelling & ignition timing maps without any correction trims being applied. These allow the car to run reasonably well, although it takes the edge off performance & the fuel consumption goes up by 10-15%.

 

I know this thread is old, but I would like to thank jaginblack for his very informative and useful post. I am going to replace both my upstream O2 sensors in a couple of days, and it's nice to know what to expect before actually getting into it.

 

I've got a severely bruised hand after all that fiddling around in such a tight space on bank 2 - beneath the expansion tank. In truth, it isn't that hard a job if you follow the instructions above by the letter, but it is SO painful relative to bank 1.

One of my torx screws just wouldn't come out, so I had to beat it out - may I recommend trying to slice the heatshield around the screw if this happens to you, as it's the softer part of the whole assembly. To remove the heatshield bracket, you can simply remove two exhaust bolts, but once again one of mine just wouldn't budge: Irwin bolt extractors might do the job, plus some applied heat.

PS, I'm thinking about replacing these torx with standard bolts (M6 x 10mm long I think), but only if the heat shield starts a-rattling now that it's on the two remaining.

What a gig! :=)

 

Spraying all with some penetrating oil and waiting ... helps.

 

The real penetrating oil versus wd40 I guess? I only had wd40 style oil which really wasn't going anywhere. I'll have to get some of the real stuff.

 

PB Blaster is what you want. It's the best penetrating oil I have ever used.

 

PB Blaster is very good -- that's what I use. Although with enough time the WD40 normally works.

 

I went through this today and to the OP thanks! Made a bear of a job a bit more pleasant and less time consuming.

CE light appeared about a month ago with no apparent change in engine performance. Lost track of my laptop to OBDII cable and let it slide for a bit. Inspection is coming due and the cat was becoming a bit sluggish, so I buckled down to fix it this weekend. 2003 XJR.

Bought a self contained reader - very convenient and worked for both the X308 and BMW E36:

Code Reader $34:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Code came back as 1647. Oh great, the hard bank. Swapped the O2 sensors on the wiring harness and the code changed to 1646, thus confirming a bad sensor.

I took the OP's advice and hit Harbor Freight for the O2 crowfoot socket and that nifty ratching 3/8" breaker bar and a 20% off coupon:

3/8" Offset Oxygen Sensor Wrench

3/8" Drive Ratcheting Breaker Bar

The socket and that breaker bar are a perfect match for this job.

The O2 sensor has gotten a bit pricey, the local Autozone was only 5 bucks more than Amazon ($90):

Bosch Oxygen Sensor 15627 - Read Reviews on Bosch #15627


In this rare case, I don't think the supercharged is any worse than the NA. I simply drained the radiator into a clean pan, removed the coolant tank being careful with those plastic hoses and removed the three torx screws holding the heatshield on. The heatshield screws were the worst. With the heatshield unbolted it was a matter of futzing with it enough to get it out of the way. In my case, the throttle cable was in the way of the breaker bar. Unbolting it from the throttle body gave enough room. I didn't take anything else apart. Put the O2 socket on and then used the breaker bar to back it out. It took a bunch of small steps and removing and reapplying the socket. Assembly was reverse of disassembly. Poured the drained coolant back in.

Power is back and the check engine light is out with no pending codes. Pictures below. No flowing blood, but lots of scrapes. Southern car, so no penetrating oil required.

-Mike

 

Hi

Long time no reply from me due to life and work and being very lucky with my Jag so far :-)

Does anyone have a video of replacing the sensor under the expansion tank? The written instructions kind of make sense to me but I have very basic knowledge of the oily bits under the bonnet.

I have the CEL and need to do that probe in the next week or so. I've read around and got the one from an X type or Mondeo (can't remember which, I bought it nearly a year ago) and for the UK a CEL light staying on is an MOT fail so it has to be done.

I'd ideally like to evaluate whether I can tackle it myself or if I need to pay a garage to do it for me.

Thanks

Joe

 

Hi Guys, i just done this on a UK xj8 with code 1647, dindn't find it too much of a pig.

My only issue is now that my revs fluctuate since changing it. code was reset and has since not reappeared, i have tried a hard reset but no luck and when i unplug the sensor the revs go back to normal. could it be a bad sensor? or could the other sensors be interfering. i bought it off of ebay as a genuine denso sensor but i'm not sure it was? any advise would be great. Sorry for jumping on an old thread


ps my car is 2002 xj8 x308 3.2 xjsport

Thanks Guys

 

You may need to drive it a bit for it to recalibrate, should only need to go up to 50 miles.

You may want to review this write up... https://www.jaguarforums.com/forum/x...cement-195018/