2006 XK8 approaching 108,000 miles....

My wife called from the road yesterday reporting the amber check engine icon illuminated and "Restricted Performance" displayed on the dashboard message center. I told her to finish her errands and then bring the car home to me. Once she returned home I allowed a brief cool-down period, then used my generic scanner to pull codes P0171 and then the expected P1000. Knowing that a P0171 code can result from a dirty MAF sensor (among other possibilities such as a faulty oxygen sensor or even a vacuum leak), I pulled the MAF sensor, cleaned it with a healthy shot of MAF sensor spray cleaner as I do every 30,000 miles or so (last done at 90,000 miles on this car), looked for any obvious breaks in the plastic accordion air duct between the airbox and the throttle body, found none, and topped up the cells in the battery with water just in case (only one cell actually needed more water). Re-installed the MAF sensor, used my generic scanner to successfully clear the codes, then took the car out for a five-mile test-drive. No warning lights illuminated, no dashboard messages appeared, just a successful test-drive with a normally-operating 4.2 XK8....

Returned home, parked the car, headed back inside and told my wife to watch her dashboard during the next few days and report any additional problems to me....

Fifteen minutes after leaving home this morning she called to say that the amber check engine icon came back on, as did the "Restricted Performance" message on the dashboard. After a few seconds she reported that the "Restricted Performance" message disappeared but the amber check engine icon remained illuminated. Again I told her to finish her errands and then bring the car home to me. I assume she will show up by early afternoon....

Since cleaning the MAF sensor temporarily resolved the issue for me, do you guys suspect a failing MAF sensor? What about a failing oxygen sensor and if so, which one and where would it be located on the 4.2 engine?

Any other suggestions are welcome. Her car is due for its annual inspection this month and it cannot pass with an illuminated check engine icon....

 

You only have a code for one side so my suggestion would be to add a fuel additive first then see what takes place.

Gus
www.jagrepair.com

 

Gus,

Thanks for your suggestion but please explain your rationale. Do you suspect a fuel injector issue? For the record, a 20-ounce bottle of Chevron Techron goes into the tank at every oil & filter change / tire rotation (6,000-mile intervals)....

 

The best at this point would be to get more data. Check the fuel trims on both sides. Also, check the fuel pressure, manifold pressure and air intake temp. This is all available over OBDII with a cheap ELM327 and Torque Pro.

You have found the book on these codes, right?

X103_P_DTC_OBDII_R1.pdf

Best of luck, keep us posted.

 

Update:

My wife arrived home about 45 minutes ago. I let the engine bay cool off a bit, hooked up my generic OBDII scanner again, and now I'm getting both the P0171 code and the P0174 code along with the expected P1000 code. So unlike yesterday, today both banks 1 and 2 are throwing lean codes. I went ahead and cleared them for the time being....

Given this new information, what do you guys now suspect?

 

Regardless of having one or both codes I recommend a fuel additive. The reason I suggest the treatment is that the P0171 & P0174 and an indication of a lean fuel mixture and that can be caused by a poor fuel presentation to the engine combustion chamber. That being said I look directly at the injectors an a fuel additive is a good first approach. You only reporting one code I would look at and injector or injectors on one side or an O2 sensor but having codes on both sides is unlikely but possible. You say you have been adding a fuel treatment so you may be ok with the fuel presentation. Just as a side note I use BG44K because I found it to work the best regardless of how others might feel.

Another cause of a lean code is a vacuum leak and you can try to find it using a can or two of throttle body cleaner and spraying it around but the best way is to do a smoke test. Another cause is the MAFS but with only one side then now two sides it is it is failing but that MAFS is one unit that affects both sides. Could be bad but not sure! I would also be checking your battery voltage. It can play tricks on the cars computer systems.

I am in line with the suggestion of getting more information such as fuel pressure, fuel trims manifold pressure among others. This will help you to narrow down the cause of your problem.

Link http://jagrepair.com/images/AutoRepairPhotos/P0171.pdf

Link http://jagrepair.com/UsingFuelTrims.htm

 

+1 fuel trims. The LTFT could be almost 25 and not set the code, so you might have been right on the edge.

 

Use this test to check your MAFS to see if it is in line.

Link JagRepair.com - Jaguar Repair Information Resource

 

Check the Battery Voltage should be around 12.5. if it is around 12.5 then do a hard reset

 

I recently had the identical codes and messages on my 2003 XKR. I cleaned the MAF sensor, which I do a couple of times a year, but that didn't help. My fuel trims were high but I could not find any air leaks. I took the car to an indy garage and they replaced the MAF sensor, which brought the fuel trims down to where there were no codes being generated, but there was still a small leak somewhere. I asked the guys to continue to troubleshoot and they found a leak in the EGR valve. Replaced the EGR valve and that fixed the problem. Fuel trims are right where they need to be and the engine runs great!

 

Hold on. Most codes (incl those ones) need 2 warm ups to flag.

So clearing them and it drives fine on one drive is "it hasn't had a chance yet".

Have a look at the fuel trims to see if you've an air leak and how alike the sides are (or aren't).

 

Update:

Late yesterday afternoon I wondered if perhaps I may not have used enough MAF sensor spray cleaner in all of its various nooks and crannies. So I removed the MAF sensor again, liberally sprayed every crevice on the sensor while holding my thumb over the electrical plug socket, let it air-dry for 5 minutes, then repeated the process. I then let the sensor air-dry for 10 minutes, re-installed it, then took the car out for another test-drive. This time I drove a full 15 miles, not 5 miles as I did the day before. No warning lights, no dash messages, no codes triggered....

If there is indeed an air leak or a problem with a different sensor, I would think it would have triggered lights, messages, and codes well within a 15-mile drive. But based upon what JagV8 posted above, we'll see if they flag again today....

 

Update:

Two more drive cycles completed this morning for a total of 15 more miles. No warning lights, dashboard messages, or codes thrown. I hope my more thorough MAF sensor cleaning yesterday afternoon indeed did the trick. Time and more drive cycles will tell....

 

Only time will tell.

 

That is another thing, I suppose: the cleaning could include contact cleaner as well for both the sensor side and the harness side.

 

Yes, it could. I did not clean the electrical contacts either time because they looked brand new, but if I have to remove the MAF sensor again, I will indeed clean them with electrical contact spray cleaner....

 

Honestly, the last time I had a similar issue with those same codes the only spray I used was the electrical contact cleaner on the whole MAF sensor and it worked perfectly (in that the codes never came back)...

 

Sounding good. Hope it's fixed.

 

Just out of curiosity, I wonder if a dirty MAF usually first shows up as a P0171 ? I have not really paid attention to any correlation, but it sounds sort of like it.

 

I know that on Toyota/Lexus forums, a code P0171 almost always points to a dirty or failing MAF sensor. Not yet sure we can echo that here on the Jaguar forum....