My newly acquired 2006 XKR Victory Edition Convertible with 86k miles is driving me nuts. If I drive her like a grandpa (which I am), accelerating adequately but modestly, all is well. However, if I put the pedal to the floor just to hear the supercharger whine, I am allowed a couple of quick bursts of speed, then the amber Transmission Fault warning comes on, and the ZF gearbox defaults to only 5th gear, and we limp home. If I then turn the engine off and then restart it, the fault has disappeared, and all is well with full gearbox functionality until the next time I let her off the leash at full whine.

If I check the fault codes, I get the combo of P0730 (Gear ratio fault) and P0735 (Fifth gear ratio fault). The DTC Guide posits “ECM Torque signal fault”. No other relevant DTCs appear in my scans – zero complaints about the ABS or the speed sensors, and the cruise control works perfectly during all this.

The only other DTC complaints are from the CATS (all four dampers have open circuits, so the suspension has defaulted to the firm setting), and Parking Aid has one bad sensor on the car's bum. Surely these faults can't impact the gearbox?

A couple more pieces of data: I did jack up the rear to waggle the wheels to detect any wobble in the wheel bearings (known to affect the speed sensor outputs) – but the rear bearings were solid. And just before the sale, the previous owner had drained, replaced the transmission pan and filter, and refilled with ZF LifeGuard 6 transmission fluid, so all that was fresh.

Does any of this ring a bell? Any suggestions on what direction to proceed? It's a bit boring to have to drive an XKR like a grandpa (or grandma).

 

Ratio faults are usually caused by a slipping transmission. However, you can check the fluid level first. Also, do you know if the PO changed the sleeves? The car's almost 20 years old and those sleeves are probably hard. It's not a difficult job. When they get hard there are leaks between the mechatronics and the trans body and weird things happen.

The sleeves are "rubber" passages between the mechatronics and the trans housing. You remove the mechatronics, pull the sleeves out of the trans housing, reinstall the mechatronics, and refill the trans. It's a bit messy but not complicated. The same trans is in lots BMWs and it's a routine maintenance item after a few years.

 

Put some Dr Tranny in it . Two tubes

 

I think he is most likely to have low ATF levels. Check for leaks at the mechatronic connector sleeve or the bell housing area. If no leaks, go ahead and do the seals Y2KJag mentioned as well as the solenoids while you're in there. Refill with fresh Mercon SP. There's a specific procedure regarding temperature the transmission should be at for correct fill. Look it up if you're going to do it yourself.

 

I had that once or twice on a long journey up to Scotland and back it was very frustrating. I've had a fluid change and the sleeves changed and the connector block connection the Mechatronix unit to the transmission changed at an independant and not had that problem since. I think in total it came to just over £400 or so which I thought was very good value.

 

Many thanks to @Y2KJag, @Pistnbroke, @giandanielxk8, @Kuddlesworth for their helpful advice. I now have several avenues to pursue. I will start with the simplest first: check the transmission fluid level.

 

This is not so simple. There is no dipstick for the transmission. Only way to check is to drain the fluid and measure how much came out.

Also, if the wrong fluid is in the transmission, it will cause all sorts of faults.

The only ATFs confirmed to work on the 6 speed transmission are:

• Motorcraft Mercon SP (original fluid with red dye, and can be bought at a reasonable price.
• ZF Lifeguard 6 (original fluid; expensive)
• The Jaguar branded one, which is the same as the above but much more expensive.

 

Oh, those were the days when we had transmission fluid dipsticks, and you could fill from the top.

 

Yep, my two vehicles both have transmission dipsticks (1999 Ram and 2013 Outback 3.6R).

My wife's two vehicles do not (2006 XK8 and 2015 RX350).

Guess which two vehicles I prefer....

 

Let me say, with all respect, this is incorrect. The ZF transmissions have their own weird way of checking level and filling properly.

The transmission has a fill plug on the right side, rear. It's an 8(?)mm hex plug with an o-ring embedded.

To check fluid level you must start from a cold transmission. Start the car and warm the trans to between. 86 and 122 degrees Fahrenheit. When the trans temp is within that range, you remove the fill plug. If the fluid comes out in a thin stream the trans is full. If it gushes out, it's overfilled and you can let it drain until the stream is thin. If nothing comes out you must add until fluid begins to come out. This may be the silliest method ever designed, but that's the way it's done.

The same holds for after you change fluid. You fill the trans until fluid comes out. You then start the car, run through the gears, and wait until the trans is between those temps, remove the plug and fill until it dribbles.

This job requires either a scan tool to monitor the trans temp, or in a pinch you can use an IR thermometer gun and monitor the pan temp. You also need a method to pump the fluid into the trans. Those are available on Amazon for not much money.

Lastly, Liqui-Moly 1200 ATF is also correct for these transmissions. I use it in my Jag and both my BMWs of the same vintage.

 

I didn't know about the fill level plug.

However, regarding the Liqui-Moly Top-Tec 1200, I had it in my car and it caused all sorts of gear shift issues: slipping gears, random codes, slow reverse. When I switched to the Mercon SP, all those problems were cured. And yes, I had done the proper fill procedure with regards to the temperature. I'm not giving that ATF a second chance not an I recommending it.

It's been reported here before that many fluids claim to meet the spec, but they always cause some issues in these Jags. The same holds true for the Redline fluid.

 

Agreed. Mercon SP ATF is the only true alternative to the still-ridiculously-priced ZF Lifeguard 6 ATF (infamously nicknamed "Liquid Gold" due to its cost). Been running it for nearly ten years now (three separate drain-and-fill intervals during that timespan) with zero transmission problems. Mercon SP is essentially Lifeguard 6, just colored red instead of amber....

 

Not to start a "which oil is best" debate, but my experience is diametrically opposite this. BTW, I use Mercon 6 in my SN95 Mustang, so I am familiar with it and it's good stuff.

The 5HP24 trans is a German trans made by ZF and is identical to the trans backing up an entire generation of BMW E39s, E38s, several Audis, and a Range Rover or two. When I'm not doing my regular work, I part-time in my friend's BMW/Audi/Porsche shop. With a few narrow exceptions, we use Liqui-Moly products in all our oil services and trans services. We have had zero issues with it.

Personally, I use it in my E39 and E46. I repaired my 2000 XK8's trans and am using LM 1200 and the trans shifts like a new car.

I'm not knocking Mercon, and I don't have a dog in this fight. I'm just saying that LM products (which are made in Germany) work well in German transmissions.

 

You're talking about the wrong transmission. Your car is a 2000 XK8, the OP's car is a 2006, which like mine, has the 4.2L engine that was mated to the ZF-6HP26, not the 5HP24. The 5HP24 was mated only to the 4.0 NA cars. The 4.0 Supercharged cars got the Mercedes 7.22 transmision.

The Top-Tec 1200 that you mentioned isn't even the correct fluid by Liquid-Moly's products for the 6HP26, that would be the TopTec 1800 fluid in their product line. Despite that, the 6HP26 is very finicky with regards to fluid whereas the 5HP24 is more lax about that. It doesn't do well with multi-spec fluids such as the Liqui-Moly, the Redline, the Valvoline MaxLife, etc. It works somewhat in that the car will run, but it will shift poorly. The fluid viscosity is ever so slightly wrong, the friction modifiers and detergents are not quite right either. Instead they use a formulation that provides a middle ground for all the transmissions that have similar but not identical fluid requirements. Some transmissions can handle such differences, but the 6HP26 is not one of them.

My experience with the TopTec 1800 is that the car ran ok for the first 3000 miles. At the time, I did the full service: solenoids, mechatronic connector sleeve seal, bridge seals, oil pan and gasket. Afterwards, the shifting became progressively worse. It would slip into 3rd and from 5th to 4th, it would be slow to engage reverse, and would occasionally throw a random Transmission fault. After 10,000 miles had elapsed, I was thinking my transmission was junk. I tried a last ditch effort in which I once again did the same service (the solenoids, the mechatronics connector sleeve seal, the bridge seals, oil pan and gasket), but this time I filled the transmission with Mercon SP. Lo and behold, all of my transmissions faults were cleared. The shifting was now crisp, smooth, and quick. Reverse engaged immediately, and I have since driven 5000 miles without a single issue.

The Mercon fluid that works on these transmissions is Mercon SP, not Mercon 6. Mercon 6 would be even worse for this transmission than the TopTec 1800 or the Redline. The reason why Mercon SP works so well is because the Ford SR80 transmission is a nearly 1:1 clone of the ZF-6HP26, and it was used in the SN197 V6 Mustangs, F150, and Explorers, from 2011 to 2017 and they still use it in the Ranger. The fluid Ford specified for the 6R80 transmission, which as I have said is their version of the 6HP26, is the Mercon SP. That fluid is only designed to work with the 6R80 and as a result, on the 6HP26. In reality, the only difference between the ZF Lifeguard 6 fluid and the Mercon SP is the red dye used on the Mercon SP.

Checking on Amazon I also found these prices:

• 1 L of ZF Lifeguard 6 is $27.65
• 1 L of Liquid-Moly TopTec 1800 is $19.80
• 1 qt (0.95L) of Mercon SP is $14.95

So now the question is, if Mercon SP is the same stuff as the OE fluid, but which a much cheaper price tag, why take the gamble on other fluids that may or may not work?

Also I'd like to add: if memory serves me right, I've seen a dipstick kit for sale online that could benefit those with the Mercedes 722 or the 5HP24. I'm not sure which of those two transmissions this applies to. This dipstick is only accessible from beneath the car, and I believe that on one of those boxes (not sure which or if both) it requires removing the fill plug to place the dipstick and check the fluid fill. It's not a dipstick that sits there permanently.

 

Your are correct. My apologies. I missed the 2006 part. OP does indeed have a 6HP26, which does use LM 1800. My point still stands. This trans was used in loads of E60s, E90s, Land Rovers, Hyundais and Fords. We use 1800 in all the E60s and E90s we service. The most common issue are perished sleeves between the Mechatronics and the trans body, which will cause weird errors. Again, zero problems with this fluid in German transmissions. If you're happy with your fluid, by all means use it. But we have loads of experience with these transmissions and have never had a trans come back due to incompatible fluid.

One question - did you do the trans service personally? Or did you have a shop do it?

 

https://meurosport.com/5HP24_Dip_Stick.php

For the 5HP24 in the 4.0L models only.

 

a lot of very good information for the OP’s 4.2 L XK-8 transmission, and also for pointing out that the 4.0 XKR’s have a completely different transmission than the 4.0 XK8’s; The 4.0 L XKR’s using the Mercedes 722.6 unit.

The fluid required for the Mercedes 722.6 transmission (4.0L XKR only) is also one that does not lend itself to substitution. I won’t list all the approved fluids here as they can be found with minimal forum searching. Suffice it to say, just use one of the approved fluids. The 4.0 XKR transmission will not function properly with a fluid not on the approved list (I did discover this the hard way).

I will only add that the dipstick referenced that is used from under the car must be for the XK8. The available dipstick for the XKR is inserted from above, and therefore quite long.

Z

 

On both accounts I did the service myself and followed the official procedure to the best of my ability (with an IR thermometer instead of IDS/SDD). Yes, I already knew that this trans is available in loads of BMWs, Land-Rovers, etc. As you said it is also available in Fords, and we in the forum have had good experience with Ford's official fluid. Again, I don't see a reason to spend more on Liqui-Moly, especially with my experience. The only reason I did so at the time was because I could not source the Mercon SP locally and it was sold out on Amazon.

 

Again, I don't have a dog in this fight. Use whatever you like. My original point was that LM works fine in German transmissions. It's more expensive than some, but much less than the Jag/ZF product. I prefer it and have had excellent results.

One thing, and this is a serious question. If you weren't aware of the fill plug as you stated earlier, how were you able to put fluid in?

 

I was aware of the fill plug, and that is how I filled it. Yet never thought to use it to check Fill-level as you would with a dipstick, like checking to see how much fluid had leaked, which is what you implied. When I first read your statement, I thought you were talking about a separate plug for checking fill level instead of the one for filling the transmission. In hindsight, it was a brain-fart on my end.

Even then, it feels like a clumsy and inaccurate way to check the fluid level.

Also, it is feasible and less messy to fill the transmission through the transmission cooler hose that connects to the radiator. The only problem with that is you may over or underfill the transmission.