i first had the dreaded P0174 lean / low voltage code on my 2006 XJ8L 4.2 liter V8 The Mechanic has replaced all the O2 sensors and the Maf sensor and the fuel regulator and now i have a code that says my cat is bad!! the issue is growing and no one can seem to find out what the issue is. The car is quiet, runs strong, good gas mileage no exhaust leaks and they cannot find any vacuum leaks. yet the light and codes keep coming back!! Now i went from having a lean condition to having to replace a Cat. i am starting to really hate this car. I have researched how to find the problem and they are just drawn out waste of time. They talk for half an hour and then it does not help. i am at a loss as what to do next. i am trying to avoid the dealer. they will invent things to replace i have heard horror stories about Jag dealers. i really do not want to have to go to one. does anyone have any other ideas? I have gone to 3 shops who work on Jaguar and they can't find the problem. Now what?

 

Check for an exhaust leak prior to the 02 sensors (mounted on the cats)

Cheers
34by151

 

It sounds a bit like a change of mechanic might help.

 

What is the age of the battery?

 

The Battery is new.

 

If the code is only P0174 it means it's limited to bank 2 (the left side). Switching the O2 sensors and seeing if the error moved to bank 1 would have been a free test for the O2 sensor.

A bad MAF would generally throw codes on both banks (P0171 and P0174). Likewise a vacuum leak in the intake system before the intake manifold splits to either bank should trigger both. I'd look for a vacuum or exhaust leak limited to bank 2.

Best to check the fuel trims in real time to see how they respond to RPM changes. Much has been written on this forum and elsewhere on diagnosing fuel trims to help determine problems contributing to lean conditions.

 

What additional DTCs are showing other than the P0174? Does the vehicle also have P0430?

At any time did the MIL flash whilst you were driving?

 

No the MIL has not flashed while driving. it just pops on.