Transmission fault light/reading computer

I’m working on the wife’s 94 XJS 4.0 liter I6 w/auto trans. does anybody know how a layperson can read the fault light for the auto trans? I don’t even know where or if there is a docking station to read the transmission computer so if anyone has some helpful insight into my issue any and all info will be greatly appreciated.

  Thank you for any help I need it!!                                                                            

Do you see an OBD2 port under the drivers side dash?

PDU is the only thing I used to diagnose older OBDI Jaguars when I worked at the dealer.
WDS was SUPPOSED to have the software because they sent the connectors but we NEVER got it.

Thank you for your reply only one problem this 94 xjs does not have an OBD connector there is a round fitting in the trunk behind the right hand side tail light it looks like it could be a connector I don’t know but they’re two different CPUs there’s the CPU for the engine and car and then there’s a CPU for the automatic transmission

Would a trip computer show the code. I know that wasn’t a standard option for the six cylinder…

Don’t bother looking for tranny fault codes in your banger, just describe the problem. Your tranny is most likely ZF 4HP-24 with electronic block (solenoids). Most of the problems are related to single solenoid rather than mechanical damage. These are not advanced hence no specific fault codes available.
Keep us updated.

Thanks for the info you know you are the first person to say what I have been thinking all along because when we first got the car it shifted like it was stuck in sport mode and the light was on then I drove it again and the light was off and it shifted great but then it sat for about week and when I drove it again it shifted hard and the light was on again do you know how many solenoids there are and are they located in the pan.
Thanks alot you really sound like you know your Jags

Specific codes are available, you just need the correct tool to read it.

I had a problem with my ZF 4HP24 transmission. Car told me it was Solenoid B.

The shop I took it to had an entire transmission valve body from a 1997 XJ6, which has the same transmission. They ended up simply transplanting a known good valve body into my car, rather than replacing the reported bad solenoid.

Codes are there, but without being able to read them, you’d have to go trial and error…or find a spare valve body and swap that out.

I still think a trip computer will reveal codes on non-OBD2 cars.

Thanks for the reply Banger I had the car at the transmission shop yesterday and they said that they would have to get the right plug for the transmission computer and they were in the trunk by the right side tail light so I think I will wait and see what they say it is.Thanks loads I’m glad you answered my call!

Martin, Vee

  1. Changing the entire valve block is always a half-measure, especially if you’re not considering rebuild with total cost involved. Valve bodies may look the same but they’re not. Every model is build to different car spec, different shifting point, even different diff ratio.

  2. Martin. The fault codes from the diagnostic socket are generic, won’t tell you or the workshop what’s actually causing these unless truly obvious fault is involved. You need someone with skills and experience/manual inspection. Don’t let the scammer sneak into your wallet, especially true with these days workshops.

  3. Always ‘start from the plug’ - when was the last time you’ve changed ATF fluid in your tranny? What’s the condition of the fluid on dipstick? Can you hear any obvious clanks/unusual sounds? How’s shifting and most important what’s the mileage of your XJS?

My advise - don’t approve any bills prior to making sure these are really needed…

All I can say is that the car doesn’t make any noise from the transmission and if I put it through it’s pace’s it will flat go through all the gears with no effort the only thing that it’s doing is shifting hard from first to second and less hard to third and almost can’t feel transmission shop I have dealt with for about 40yrs. they want to pull the codes to see what way to go plus they have a x Jaguar mechanic on staff thanks for all your advice it’s greatly appreciated

Thank you very much


I am not knowledgeable enough to know if swapping valve bodies is a bad thing, but it has worked for me, at least so far.

I got a two year warranty, so I’m happy. I think I’m one year in? I recall being told the valve is common, the Tranny ECU is what makes the difference between Jaguar cars.

So far, so good.

I did take the old valve body with me. Haven’t done too much with it, other than test the solenoids, and they seem to bench test just fine, including the reportedly failed Solenoid B.

If you don’t mind me asking how much did you give for the new valve body?

I believe I paid $700 for swapping out the valve body, replacing trans fluid and filter as well.

I had to pay for the labor to get the 97 XJ6 on the lift to remove that valve body.

I may be able to find that receipt, but that would happen later this week.

Actually, found this:
$260 in parts, 5.7 hours for replacement and diagnosis.

That means it was closer to $1,000


What’s the mileage, odo-odo-odometer… Is it in miles or kilometers…
When was your last gearbox fluid change - helloooo?
You will have dirrefent diagnostics of symptoms on tranny with 140k, different under 80k-ish…
Hard shitfing is almost always related to fluid pressure inbalance on the valve block. Fluid pressure is controlled by solenoid, hence my question. With higher mileage you may suspect mechanical failure or pressure damage on the clutch baskets - however that originates from valve block issue and valve block issue almost always originate from: fluid not being changed for decade -or- ‘trusted’ workshops using rubbish fliud during the change.

Hard shifting on first gears is usually valve issue on high mileage models - usually wear of the valves in 4hp22 (mechanical valve block) or wear of the valves+plus product of wear stuck in pressure solenoid of 4hp24. No-brainer is the fact that these are the most used, hence normal deterioration.

Slip shifting (but still shifting) for example suggest damaged clutch plates more likely the friction material is almost gone. Alternatively one of the clutch basket’s seals leaking (uncommon).
Vibrations on the first gears may also suggest former drag racer owner (glazed metal clutch plates or partial damage/inbalance of friction plate/s).
These are example that can alao co-exist and you cannot apply them directly without full picture…

With low miles models I would go for triple fluid change to start with. If you’re on budget - flush with cheapo 2-3 times (1 change of fluid every 50ish miles of city ride), then go for good ATF fluid (another 3 changes).
If you’re not a master of half-measures - I suggest 3 changes with RoyalPurple Max ATF to start with - this stuff makes miracles. No, not ATF fluid change in your 40years known garage, unless you will witness what they’re pouring into your tranny. Remember that most of the automotive stockist no longer supply anything that is even close to Dexron 2 or 3. Yes, the spec would say it’s ‘compatible’ - whatever it means - who gives a toss about fraction of the fraction of these days market…
Have a read below, just to understand triple oil change:

Vee, so you’ve got refurb one, price of $700 kinda confirms that (hopefully).

In terms of solenoid test method - I wonder how you’ve tested them as they appeard fine???

It wasn’t even refurbed, it was literally pulled out of a 97 XJ6 and installed right into my car.

Refurbished, to me, means some work was done to clean and replace worn parts. I got none of that.

Like I said in my previous post, parts were about $250 plus 5.7 hours at $110/hour….after some taxes that’s probably closer to $1,000.

As far as testing, I placed 12v to the right wires, hearing the solenoid click. The electrical diagrams on helped me figure out how to check it.

Wow, you know this crap in UK is literally on every junkyard? $700 for donor unit is truly extreme… I always thought that US market is specialised in automatic drives. Makes sense to export these as a full-time job…

For sure I just paid $32.00 for two OEM sun visor clips.

It was $700 in labor.

I was charged $260 for the valve body, a new transmission filter and fluids.

They charged me for the time to remove it from the XJ6, and then the removal/reinstallation on my car. 5.7 hours, including the filter and fluid, which all adds up.

I know these valve bodies are common in the UK, not so much here though.