I am gonna start this post off with an apology. I hate memebers like myself that come on and post a question without fully researching. Reason why I am posting is I work 27 days on 1 off. 12 hour shifts. I know my way around a car. I have done the "impossible" twice. One was a 5.4l powered Lincoln town car and the other is my f150.

Anyway today was my one day off and I drove about 200 miles (each way) with my father so I could buy a 2000 xk8 with 120,000km or 75,000 miles. Chains and tensioners have been done.

Now while driving home we were agreed to stop at a small town on the way home approx half way. The car ran and drove flawlessly on the test drive. When we approached the town I slowed down, pulled in, my father behind me in my dodge truck. When I went to pull in I got.

Fail safe engine mode, gear box fault, asc not available.

I ended up unhooking the battery in the truck for a couple mins. Hooked it back up, faults went away. Away I went. About 30 miles down the road from there we went through another town which required me to slow down to 50kmh or 30mph. Once I hit that speed. Same thing happened. But this time a check engine light came on. The car idled erractly withe the same faults came on. I shut it off for 5 mins. Turn the key. Check engine light comes on but the gear box fault, trac fault etc were gone. This occurred 5 times on the way home.

I've seen that the throttle body itself may be a culprit. I opened up the throttle body manually and saw that it was spotless inside. I also unplugged and cleaned up all 3 electrical connections to the throttle body assembly.

After doing so and the car sitting in my driveway. The codes are still present along with the fault codes. One other thing I noticed is that the butterfly for the throttle body itself is cracked open a hair. I can physically push it down a a little bit and I believe I can see where an idle air control valve would be plumbed in under the butterfly. I really don't know where where to go now.

I will apologize again but would really like to see my future off day off machine be up and cruising around again. Ny neighbour may have a scanner that will work on this jag but right now my Mac tools one will power on but will not communicate with it.

Thank you again

 

buy a handheld code scanner and get the codes and post them, that is the best way to get answers.

sometimes you can borrow a scanner from some parts stores

 

+1. It is just guesswork without scanning the codes on these cars and can cost you much wasted time, money and aggravation. A code reader is an essential tool for repairing these cars.

 

+1 on advice given. A weak battery can also cause many issues for the electronics.

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enjoy

 

Hello,

I don't know if this will shed any light on your issue?

https://www.jaguarforums.com/forum/x...x-fault-44039/

 

If you own an XK* up to 2002 there are two ESSENTIAL spares you should also buy (and keep in the boot). A spare throttle body, and the circlip pliers to undo the water hose clips to the body. The problem is 99% certain to be either the TPS or the PPS on the throttle body. I had mine trip out if I drove at 76mph. If I avoided that speed it was fine.

If you have cruise control it overrides the TPS - so engage CC and set it at the speed your car is tripping at - that gets over the problem but isn't convenient.

Get a 2nd hand TB from Ebay - pick one that says it tested - but check which version you have. One type is vac operated (black cylinder next to the inlet), and the later one is electronic (no black cylinder). If it fixes the problem, throw the old TB away and buy another spare.

Reading codes is all very well, but to read them properly you need to spend a LOT of money - and even then interpreting the results amounts to guesswork. Better to pay an Indie (or any decent independant garage) to read the codes for you.

 

And one other thing - the seller knew about the fault as it's obviously 'resident'. I'd have a word with him about the cost of replacing the TB.

 

I ordered a scanner that will work with this jag. Will be in tomorrow. I will read the codes then. Something that should be known is right up until the time it screwed around on me pulling into the driveway. The asc/ gear box/ trac faults would go away after couple minutes sitting. Today after work went to look at it and the faults came on instantly, without even starting the car.

One more thing about myself. I am very mechanically inclined and seeing how this is not a daily driver I am the guy that if something has proven to fail on me I am the guy that will rip it apart and see which part has failed. I will also post a how to. One thing I will say is that this throttle body has a striking resemblance to the Mazda cars that I have raced.

 

Good move to get the scanner and therefore the codes. Your description of the way the fault occurs is exactly the way the TB(or more precisely the TPS) failed on my car - it took me a time to realise that it usually did it as I came off the gas. The tracks on the TPS wear more at the start of their travel(where they are used the most) - think crackle on the old radio volume controls. The TPS is a dual track offset output and as soon as the ECU senses an incorrect output it throws the limp mode. If it is the TB there are repairers rather than buying new at ouch $. Just a heads up - post the codes when you have them.

 

Are you guys ready for this....

Ok. I ended up taking half the day off here to look at this unit. I got myself yet another pricey scanner. I had to update which took a while. Then I hooked it up went to read the DTC's. no communication with the ECM. Pissed off at the world. I went through the scanner and found I could read the TCM and ABS modules. Codes I got p1797, p1632, and u2500 (can bus no communication with ECM). Bonus I had some where to start. Hit the search function and got a lot of weird responses. I mean weird "fixes". One kind of caught my eye that so simple and easy to try. I figured why not. I've done worse things in my life. The suggestion was to unplug the relays under the hood located near the ECM and plug them back in.

I did that and BAM instantly everything on my dash was gone except the CEL. went to plug my scan tool back in and still no communication to ECM. I made some progress though. I decided to unhook the battery to hopefully reset the mystery CEL. Hooked it back up. People on here are saying no communication leads to ECM replacement at $6000 (this thing would have undergone an LS swap before that).

So. With those 3 codes in hand and the mystery cell. At a loss for words as to why i couldn't get communication, dreading a dealer visit. I went and took a picture of something "odd" that I noticed in the relay blocks under the hood. There was one relay that had been replaced. I was literally going to take this picture ask what this relay was for and leave it at that.



Before I did that I figured what the hell. Unplug it again, plug it back in and see what happens. When I went to unplugged it the 2nd time the relay holder popped off its clip. I laid it sideways to get a better up to separate. Found this.



After plugging the relay back in. Figured, one more time look for communication to the ECM. Sure as the sun always rising in the east I HAD COMMUNICATION. Code came up as p1121. I still need to repair that wire. But everything in my 5 min test ride after performed perfectly.

I am going to take it on another little cruise here about 20 mins to get some premium fuel for her and will post back here if I find anything or p1121 comes back.

 

Great find and I hope that fixes that problem. However, I do see new upper shock mounts in your future.

 

Well everything seams to be ok. Drove it around for a good hour with a few stops along the way. Car is gonna have thurough front end inspection tomorrow. Noticed a slight clunk in the front passenger side and a slight uneven tire wear on the front passenger side that I never noticed by feel (physical tough) when I looked at it before test drive.

 

any electrical issues will raise havoc in the xk's for sure... something simple like the flap where you insert the key not closing completely will trigger all manner of things in time. weak battery is another issue if not above 13 v sitting expect problems eventually. car is very prone to weak grounds clean and tighten any you come across . just some of the issues I have experienced.

 

see that upper shock bushing in your picture of the relay panel.

 

Sure as the day long. The codes came back yesterday after I tried to start it. Just p1121 and p1623? I believe anyway. A quick search on here landed me straight to the TB. I'm going to give the place a call Monday morning and ship my throttle body to them.

Quick question for you guys. Does anyone have an old throttle body assembly or even just the tps. I would like to tear it down and use mine when it gets refurbished as a known good constant to try to get to the bottom of the wear parts inside. Yes I would pay for shipping

 

Hi.


That chafed wire looks very suspect. Somebody may have been there before.


A member in our English sister forum changed his TB after a P1121. Failure code returned.


Turned out to be a bad TB pwr. supply relay.

 

It is usually the throttle position sensor or pedal position sensor potentiometers that fail (the throttle body is pseudo drive-by-wire and servo driven).

There are several threads on this. A reliable source of supply to the comsumer other than an occasional one on ebay or from a Chinese supplier has been elusive. Even if you can get one, there is no published information that I am aware of on properly calibrating it when installing. A professional rebuild is still your best bet.

 

Trust me I know all about drive by wire. When I get mine back in the mail I will make some controls and constants to test the resistance off my soon to be reman and the one I plan on rebuilding myself. It would be 6 bolts. 2 hose clamps/hoses. 4 wiring connectors and its out. Would be really to swap and test on my own once work slows down here in about a month.

 

I hope you share your findings here...it would help a lot of folks.

 

Pulled the battery as my problems are so weird right now. I am honestly thinking my battery is NFG. Manufactured may 2010. Question is. Pulled battery and foun this wire just laying there. Any clue what it is for?