The Jag fans on this forum have always been so helpful, I feel I need to take the time to write about my experience with ABS Not Available error and how it relates to the dreaded intermittent Limp Mode.
In the hope my story may save members some stress, frustration and most important wasted money hunting down the cause.
For the record I am also a Jag nut going back to the 80s when I bought my first one a 1971 12 cylinder XKE.

​​​​​​​Ok, several years ago I had to give my daughter my 2003 Volvo to commute to college a few hundred miles away. I asked my foreign car mechanic what kind of cool car can I by cheap that will be fairly
​​​​​​​reliable? I said are there any beamers, he said hell no stay away from them. He suggested a XJ8. So after hunting a couple of months I find a 1 owner trade in at a local Cadilac Dealer. The only
thing that looked a little worn was the white / Oatmeal drivers seat and steering wheel. The Dark Blue paint was as shiny as a new dime. I live in Florida so it is a garage kept car with no rust.
There were maintenance records and the car had 120K on it.

I took it to my mechanic to check that the cam adjusters had been changed. He said they had been done ( I believe that by 2002 the factory had caught that) he mentioned that it seemed like the ABS
module error had been reset, and it may have been fixed he didn't elaborate any further. I drove it maybe 0 miles that day and no warning lights came on.
I bought the car and within a couple weeks that ABS light did come back to haunt me. I said to myself big deal I know how to drive I don't need the car to brake for me so I let it go.
About a month later I have the transmission fluid changed the old fashioned way by dropping the pan. My tranny guy goes oh, oh your lifetime fluid looks like **** and there is plate metal
all over the pan. The tranny has anywhere from 30 days to a year to live.
My first issue was the car going into limp mode. I would shut it off and most of the time it would reset and be ok.
It started to happen more frequently until 1 day I am at a red light and the car stalls out in gear. I was able to start it and drop it in gear at a high rev with my foot on the break and get off
the street.
I had the tranny rebuilt for like 2,200. then took it back for a fluid change and check up within like 5,000 miles.
the tranny guy drops my pan and says hey this fluid is kind of burnt and looks like it has over 40,000 miles on it.
I said what the **** I have driven less than 5k, you tell me whats going on you rebuilt it.

I then spoke another foreign car mechanic across the street who seemed to know what he was talking about
which was evident by the mint Gull Winged Mercedes up on his lift that a customer was obviously trusting him with.
I told him my tale of whoe and when I asked him about fixing my ABS module he said that is why your tranny died.
The ABS computer module talks to the tranny and tells it how fast the car is going that way the tranny knows when to
shift and what valves to open and close in the valve body. If the ABS module doesn't talk to the tranny , the tranny burns up.
So I got the tranny guy to rebuild the tranny again for 1/2 price after I got the ABS module fixed.

This time I researched the ZF5HP 24 transmission myself, had a trans-go modification valve installed and made sure only
Pentosin ATF-1 was put in that tranny after the 2nd rebuild and also had the dip stick installed to check the fluid condition
which is easy because the lifetime OEM factory fluid Life-Guard 6 which is manufactured by Pentosin is clear.
The moral of the story is that if that Jag with the ZF5HP-24 transmission was driven with a faulty ABS computer Module
(which is a known issue due to bad solder connections) or if your ABS warning light is on now the reason the car goes into
limp mode is because your tranny is toast. (Sorry.)

 

Hi Gregg,

Thank you for reporting your experience. I think the foreign car mechanic's explanation was a bit simplistic. It is true that the ABS/Braking Control Module provides the vehicle speed signal, but that is only one of several signals required for the Engine Control Module (ECM) and Transmission Control Module (TCM) to select appropriate gear ratios and to orchestrate smooth gear shifts. Other signals required include engine speed (Crankshaft Position Sensor (CKPS)), coolant temperature (Engine Coolant Temperature Sensor (ECTS)), engine torque load (Mass Air Flow Sensor (MAFS)), throttle position (Throttle Position Sensor (TPS)), accelerator pedal position (Accelerator Pedal Position Sensor (APPS)), brake pedal position, cruise/speed control status, kickdown switch status, various transmission and gear selection signals, etc.

A fault in the ABS module can definitely trigger Limp Home Mode, which locks the transmission into one gear to enable the vehicle to be driven to a safe parking location. The whole point of LHM is to protect the transmission from unsynchronized gear shifts caused by a loss of one or more of the required signals. But it may be a stretch to blame transmission failure on a problem with the ABS module. Repeatedly driving the vehicle in LHM, especially at high engine speeds, might contribute to transmission failure, but the 5HP24 has several known failure modes including the well known ridge forming in the pressure control solenoid bore leading to overpressure and failure of clutch drum A, the defective F clutch piston, etc. As far as I am aware, these have all been linked to defects in the internal components rather than failure of the ABS module.

In your final point, perhaps you did not intend to be so definitive and broad: "...if your ABS warning light is on now the reason the car goes into limp mode is because your tranny is toast." The ABS warning light indicates one or more of many possible faults, often something as simple as a dirty wheel speed sensor. The ABS light in combination with LHM indicates that one or more of the signals required from the ABS module is not present on the CAN data bus. The transmission may be perfectly fine, but the missing signal prevents the TCM and ECM from performing smooth shifts, so the transmission is locked into one gear to prevent damage. This is the system operating exactly as it was designed.

Would it be more accurate to say that abusing this safety system by repeatedly driving the car in LHM could contribute to transmission damage? If so, the ultimate blame may lie not so much with the ABS module but with the driver who fails to have the fault corrected.

Below is the list of signals referenced by the TCM and ECM in the transmission management process from the AJ-V8 / 5HP24 Technical Introduction:



Cheers,

Don

 

Actually think it is the other way around ... the transmission is providing the input through the drive shaft rotation (constant). The ABS is watching the wheel rotation differential ... the transmission does not care what the front wheels are doing. It's watching the rears.

Strangely -- an important item is the cluster (instrument) -- it's an inflection point and that's what's distributes .... RPM and temp to ACC. The connections on the old car can be an issue.

 

I never drove the car in Limp Mode. I was usually able to just turn the car off and on and Limp Mode would go away.
It would start happening more frequently until like a stated it just stalled out at a red light and that was it for the tranny.
I am pretty sure that by 2003 Jaguar fixed the weak A-drum problem.
I can tell you this: When I had the tranny rebuilt without fixing the ABS issue it never felt right and then after 5- 10K miles
my fluid was burnt.
Since fixing the ABS computer module and having the tranny rebuilt at the same time and using the Pentosin ATF-1
I have had zero issues with the car and it drives as smooth as silk with 145K miles on it. So I am pretty convinced that
​​​​​​​the root of the transmission problems and eventual death of the tranny was the ABS module.

​​​​​​​PS I had the dip stick installed during the 2nd tranny rebuild so I could keep an eye on the condition of my tranny fluid
and it is as clear and clean today as the day we put it in. Remembering that when the tranny was rebuilt the first time without
replacing the ABS module the fluid was burnt in under 10K miles.

​​​​​​​An easy way to test my theory is that if your ABS warning light comes on even intermittently and your car goes into limp mode
which probably means you waited too long. Just drain a little tranny fluid put some on a white coffee filter or something and observe
the color and smell.

 

Sort of a related question. I have encountered the dreaded LHM a couple of times. Always managed to fix it, lucky me. However, when in LHM the car is impossible to drive. I understand it locks into one gear, which makes sense. But in my case the engine will not rev at all. I don’t get much above 12-1500 RPM if that. It would be handier, if not also a lot safer, if you could rev the engine a bit more.

Is this the normal LHM behaviour? (no gear change, low RPM)

Jeroen

 

My guess is the first trans rebuild was not done correctly. When you get a limp condition .. that's the transmission. Depending on what's the cause .. the ABS/ Traction will come on telling you the system is off. As I said one of mine will give me the ABS/Trac and the trans never changes and we get no trans warning. We have one guy who keeps saying he is going to fix his ABS .. never does .. he has been driving it for years. The limp home is for the transmission

 

There is also "restricted performance" .. the car is protecting itself. It's designed to restrict engine speed so you can pull over and still have control of the car. Frankly -- IMO it was a bad idea the way designed. Sometimes the engine is smooth other times it's very rough .. that I can explain. Have experienced both often with same car .. have changed nothing.