1997 XK8, fault codes P0790, P1798, P1722
Left the car at the mechanic to change the tires. When I picked it up as soon as I put it in drive I felt the car "jerks", gearbox fault popped up. Drove it home (on restricted performance) which was very close, at that time check engine didn't come up. Later the same day started the car, fault cleared, got it out of the driveway in reverse no issues, put it in drive no issues, let go of the break pedal and barely touched the gas, gearbox fault came up again and I could feel that transition is, for a lack of a better word, slipping as the car does not respond to the gas pedal being pressed.At this time check engine popped up with the codes I have listed above.

I am afraid this could be the end of the road, replacing transmission would be very expensive and while I could do some work on the car this would probably be outside of my comfort zone. Any help at all would be greatly appreciated.Thanks everyone.

Also, if someone could recommend a place / person in northern NJ it would be great.
ty

 

My gearbox fault was caused by a bad right front wheel bearing.
Having your tires changed could have aggravated a wheel bearing situation just enough to cause a fault or an ABS sensor on a wheel could have been banged or broken. Check all wheel bearings and ABS sensors.
This is where I would START. There is quite a list of what it could be. Good luck.

 

^^ Excellent advice....

 

Definitely follow the advice above - especially as someone has been near the wheels...

Beyond that, two of the codes (P0790, P1722) have possible causes related to the gearbox selector cable / mode switch (both are external to the trans)

 

Thank you for the suggestions, really appreciate it. i was fairly certain it was a mechanical issue given my first experience with the restricted performance. since only one tire was worked on, this narrows things quite a bit. I'll see if I could find recommendations for the sensor and bearing testing. Interestingly enough, ABS did not show up on the scanner.

Found the thread on how to find and clean the sensor:
https://www.jaguarforums.com/forum/x...ors-faq-37434/

Need to find a thread on how to test it now

thank you

 

Cleaned both rear wheel sensors and swapped left with right. Resistance on both is around 1125 Ohms. Also checked the bearing to the best of my abilities, no wobble or noise. Same as before. I should mention that gear fault resets every time I restart the car. Check engine light does not and I did not clear the codes. I checked underneath the car nothing jumps out at me, not that I am an expert. Any other recommendations? Someone recommended sending transmission module to have it checked out. I think the fact that it was sitting outside for two days while it was raining for two days might have contributed to it more than the work they did on the tire?

Many thanks.

 

Ohms is not a reliable check for such sensors - basically it's only a way to tell if a sensor is bad but not whether it's good.

Spin the wheel & watch sensor with a 'scope.

Or read the ABS module

 

I know, but I really don't think it has anything to do with the sensors.Gear fault pops up at 3 mph, plus i tried swapping them.

 

Have a look at this episode from 'TTG' showing how to check the sensors and connections in a way that JagV8 suggests, although using a multimeter to measure the output. The actual test starts at around 14 minutes in:

 

thank you for the link, will test and report back today

I was also thinking that it maybe a good idea to send the TCM out to have it checked out. Could someone recommend a company that I could use. A while back i used Automotive Scientific to rebuild my ECM, but they don't work on transmission modules. Anybody used moduleexperts.com ?

thank you

 

I doubt your problem has anything to do with a wheel speed sensor.

Since you have a selector cable code, it's quite possible the cable has stretched out of adjustment.
When you start the car and P is lit up. move the lever slowly through each gear position. Each one should lite up when the lever is in the center of the surround cut out.
If it isn't, or if any position does not lite up, I would adjust the cable until it does.

 

Thank you, this is fairly easy to check, will report back tonight. Could it be related to a broken micro switch in the J-gate?

 

No issues found, all good. Thank you for the link, very helpful.
Shifter perfectly lines up with the holes.. I don't think anything is supposed to light up on the J-gate, mine didn't lite up in any position. It is just backlit.

I think my next step is to send out the TCM to have it checked out. Any other recommendations? Thanks everyone.

 

Are the tires the same size as the old?

 

I just remounted old tire onto the rim that was used for the spare in the trunk. Rims are OEM, identical to each other, chrome was peeling so I decided to use the one from the spare that was sitting in the trunk. Should've left alone I still think that the issue is likely due to the fact that it was sitting in the rain for two days.

 

Could someone please recommend a place for the TCM troubleshooting / repair.

Thank you.

 

R, pm me if it turns out 2b a bad tranny. I'm in Princeton area, had the joy of my 98's A drum failing last year. Lots of stuff to share including NJ stuff.

FWIW I found an honest tranny shop on Perth Amboy Woodbridge area. Getting AAA to tow it down there for an evaluation. Anyone would probably charge something to evaluate it, credited towards fix price.

FWIW figure $1800 for a rebuild. I got quotes up to $5,000! I posted what I paid 15 or16 months ago. Look it up to validate my old memory if u want. I believe it was $1800.
John

 

Ty, will do. Hoping it s electronics as the car was not driven when it happened. So far wasn't able to find anybody to rebuild the TCM, will prob try to source it on eBay.

thx

 

Puled the TCM out this morning. Most of the modules on eBay are LJA241AB, mine is AA. How important is it to match all the letters?

Thank you.

 

I think y'all are jumping the gun here,,,
But that's just me.
Try looking at some threads where folks had the same issue.
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The problem coincided rain (you said), and wheel work.

When it rains do you have a known leak spot? Does it get wet under the dash or driver's foot well? At the back of the engine where a/the main harness between the engine, trans and ECU lives.