XK / XKR ( X150 ) 2006 - 2014

Fault codes P0171 and P0174

Old 01-30-2019, 07:32 PM
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Default Fault codes P0171 and P0174

Fault codes P0171 and P0174.

Hello all, has anyone had any experience of these codes? They are for ‘system running lean’ on each bank. The engine check light repeatedly comes back on once cleared in my 100,000 mile 2006 XK 4.2. Looking back at the history, I can see these codes have been showing up for several years. A leak check on the intake system was carried using a smoke machine 4 years ago with no leaks found, the mass flow meter was replaced which apparently cured the issue.

A year later the codes showed up again, fuel pressure sensor was replaced along with pipework.

The codes are back again… I have had the car for a few months and it sounds and feels healthy. MPG is only 16 or so, but I do quite a lot of short trips.

I am going to get the car serviced soon, some online research suggested it might be something as simple as a blocked air filter causing this, but I am keen to know if anyone here can offer any insight?

Thanks in advance everyone.

Last edited by paulguitar; 01-30-2019 at 07:41 PM.
Old 01-30-2019, 08:39 PM
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Those codes are likely to be caused by a vacuum leak. Your XK is 13 years old and the rubber hoses dry out and crack over time. See this old thread, beginning with Post #6: https://www.jaguarforums.com/forum/x...arging-178162/

Last edited by Stuart S; 01-30-2019 at 08:41 PM.
Old 01-31-2019, 02:18 AM
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In case it's not that, you can check if it's an air leak somewhere else:
get an OBD tool with live data e.g. elm327
get engine hot
watch LTFTs (see my sig) at idle
rev to about 2500 and watch them again

If they drop a lot it's an air leak (perished hose or whatever). If not, post the numbers and see if anyone has ideas.

Running so long with the codes may mean one or both cats are in poor shape, sadly.
Old 02-02-2019, 07:22 AM
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Check plastic vacuum lines in front by throttle body follow to radiator I had several cracks in those lines causing the codes
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