Hi everyone,
My partner and I each own 2001 XKR's.
Her's has developed a P0174 fault (142,000 miles).

Just before (a few degrees) the car reaches normal operating temperature, we get 'RP' and the MIL light comes on. As soon as the car reaches normal operating temperature (so a minute or two later) the 'RP' light goes out but MIL stays lit. If the Code is cleared when the car is warmed up then there is no further occurances under any circumstances until the car cools and is restarted and then same pattern emerges (without fail). The pattern is so predictable you can drive along and say it will show 'RP' now, it will go off now.

The air cleaner and intake right up to throttle body is fairly new and very clean. The throttle body has been cleaned. The MAFS is the original and dirty, I cleaned it and installed it in my car. My car has a much new MAFS that is clean. Despite swapping the MAFS the fault has remained with my partner's car and mine runs fine with her old/dirty MAFS...so it is not that.

I can't find any obvious vacuum leaks and based on the predictability it sounds more like instrumentation fault (sensors or wiring) than a mechanical fault.

As we have two identical cars we are blessed with the option of swapping out a component to test 'cure' a fault before buying a part or opting for a dealer repair (it has saved us thousands of pounds!)

Can anybody with a similiar experience tell me what they would swap next in the quest to solve the fault,
thanks Perry
Derby, England

 

Assuming you don't have the capability to capture Fuel Trim live data or freeze frame:

The other half of the closed loop system is the O2 sensors. They are the "heated" type. I would suggest that since you've checked/verified the MAFS isn't the problem, the next verification should be the sensors. I'd start with the upstream first as it is more likely to be the contributor to the fault.

 

thanks stevetech. I do have the ability to capture live data, but I am not sure what I would look for or what I would attribute any variation to. I thought that the upstream O2 sensor would be the next logical place given the coincidence between operating temperature and fault recognition and I'm grateful for your suggestion. Thanks again.

 

Not sure how you checked your system for a leak but I recently checked my S-Type the other day using CRC Throttle Body cleaned. I had cleared the code and had no check eng light and the engine was cold. I found it with a little help from Brutal directing me to the most common problem, I spayed all around and directly to the spot and the engine began rocking. What I liked about the TB cleaner is that it did not leave a residue and it found the problem.

I should say that my P0171 & P0174 came up only when traveling at low speeds https://www.jaguarforums.com/forum/s...ad.php?t=42429

I hope this helps!

 

Thanks Gus! I've looked at your thread and will have a go at the vacuum leak check again (because it requires the least effort) and then will make notes of the fuel trim as advised.

 

I recently had to find a vacuum leak on my 2000 S-Type and I used throttle body cleaner spray and it worked great. Found it in no time!