I am glad to have found this place while searching for a solution to a perpetual problem I have been having.

It seems that at least three times a week I get p0172 and p0175 coing up simultaniously, which of course causes my check engine lite to come on along with restricted engine performance for a short time. It was diagnosed here in corn country as a bad maf sensor, which I replaced. After a couple weeks of driving the same conditions occur with both codes coming on at exactly the same time. I have monitored the car with my obdII scanner and has seen them display together. I am wondering if anyone may have some sort of idea as to what may cause this to occur. I lean toward the fuel pressure regulator but do not want to do anything without getting some feedback first...

Thanks to all that respond and I will be happy to assist others when I can

 

it a rich condition for both a and b banks, you need to look at things that feed both, And while you didnt yr and model. That code is most often MAFS, but you need monitor fuel pressure. Even more important is your long term fuel trim may be still under old operating conditions. Disconnect the negative battery cable, and momentarilty touch it to the positive cable to provide a path to ground for the capacitors and erases volatile memory in the ecu's. Then you wont be dealing with past parameters the ecu.s use for performance changes...And yes, a fuel pressure reg. is a likey culprit too

 

...edit...

 

this sounds a bit dangerous to every operating system in the car... btw the car is a 2000 Vanden Plas. Is this a Jaguar Certified technique?

 

I followed the advice given above and within 5 minutes of driving the condition repeated itself any more ideas?

 

do you ever have to reboot you laptop or pc to fix faults and lockups? same thing. And yes, not only Jaguar, but probobly every other car out there. Do you honestly think a techis gonna disconnect a battery and wait a hour or more before working on air bags? Nope, the SRS(supplemental restraints system) module using capacitors to fire an air bag even without battery power for up to an hour. And this is how you disharge that so you can work on. The only other way to clear long term fuel trim is with a high end scanner, or Jag specific IDS. I know you probobly dont have either. And on your next post, get a fuel pressure testor nd tap into the fuel rail. If you get one with a long hose you can duct tape it to the windshield so you can monitor it while youre driving

 

You replaced your MAFS with a new unit, or a used one?

 

brand new from the dealer...

 

shameless bump....

 

when driving casually tonite I noticed the transmission seemed to not want to shift out of second gear and would run at 2k rpm@30 mph. could I be looking at a transmission module causing my troubles with engine codes?

 

No... Im with brutal check fuel pressure. Cud be regulator .. Catalyst failing. Inner fender insulation clogging intake tube.

 

A new and more worrisome issue has emerged with the car now being very hard to start. It will crank and fire, but shuts down after several seconds of running. I can keep it running by using the gas pedal, but it coughs and sputters. Disconnecting the Mafs does not smooth out the idle at all, as it did on my Chevy... At times the car will stall when driving and indicate such with a engine stalled display on the dash. There are no additional codes to display.

 

Did you manage to resolve this problem?

 

my guess, fuel pump.

 

okay i know this is an old thread guys but i'm having same issues. I just replaced the bank 2 upstream o2 sensor due to the code coming up and the car wasn't driveable...horrible idle and very rich smell of gas...replaced the o2 sensor and took care of that problem. Now I'm getting the p0175 and p0172 codes which seem to indicate fuel trim too rich on both banks like this thread states. I'm also getting the RP when this happens and the transmisison is acting funny just like the guy stated not wanting to shift out sometimes...everything was fine before this o2 sensor went bad. Did anyone find a cure to this issue? MAFS? I think mine is orginal but its been cleaned. I have a 98 XJ8 193,000 miles. All help appreciated guys! Thanks.

 

Have a read of this article:

Running Rich - P0172 & P0175 | Jeeves and the Jaguar

Seems the problem wasn't the MAF sensor or dirty pins, but that the MAF pins were not contacting the connector properly-so the guy bent the pins to make better contact & after a couple of days the problem went away.

 

okay problem solved for now it seems...took the mafs and cleaned it with electrical contact cleaner really good...cleaned plug and completely scrubbed out the breather hose leading to the throttle body. I cleaned both the part load breather tube and breather tube as per the info on the forum. I had recently done the throttle body a month ago so it was still ok. Unhooked negative battery cable and let the car sit for 3 hours while the air tube was drying...hooked it all back up and took for test drive and no codes, runs smooth and hopefully it took care of it.

 

I was getting exactly the same codes until I changed my air filter. These cars seem to be so sensitive!
Maybe try this before you try anything else.
Once per year I believe?


Change the air filter

 

Great info. Thanks