Today I got an XJS with the codes p0400, p0420 and p0430 and I just wanted to share my fix with you guys with nice pictures!!

Jaguar HELP!: 1996 Jaguar XJS I6: P0400, P0420 and P0430

 

Thanks for the information!!

Sadly new O2's did not help my 420/430 codes. I used OEM Jaguar sensors *and* had them reoriented by the old Jaguar computer.

Probably leaks in my exhaust manifold.

 

Yeah sorry to hear that but an exhaust leak should be rather loud... first check for exhaust leaks...

 

I think the AJ16 s suffer from hairline cracks at the manifold, but if your codes have not come back with those 02's I might just replace mine again

 

Manifolds-- you gotta pull the heat shield and actually look at 'em. Both mine had cracks but I never heard even a trace of noise.

Cheers
DD

 

I am pretty sure that is what I will find. My MPG has dropped horribly since these codes came up. The MIL lights not on, the codes are just stored.

Doug, did your MPG drop as well? How did you fix your manifolds?

* oh and BTW, when I say horrible MPG, I am talking about 10mpg city driving and less. Really horrible* car has got 6 new OEM coils, new OEM MAF, new upstream 02's, new CTS.

For some reason the MPG improves with colder temps..a very noticeable improvement.

If my MPG was normal I could not care les about the codes

Thanks

 

I was lucky to find a pair of used manifolds on Ebay for $125. Previous attempts at repair using "Pyro Putty" were not long lasting.

No change in fuel economy with/without cracked manifolds....or at least not enough to notice.

Cheers
DD

 

Thanks for the reply. I wonder what could be causing the astronomical fuel consumption, if not that.