auto box warning light

[chuggernought]

hi, all new to the forum and jag ownership, i have a 1989 daimler(xj40) 4.0l. after about 5 miles and nicely warmed up the autobox warning light comes on and i get very sluggish performance, i presume this is limp home mode, it will stay like this until i get home and has stood for a while, then sure enough after about 5 miles it will do it again. if i am in sport mode it will cancel this as soon as the light comes on, it also gives a hard CLUNK when engaging reverse when the light is on but not normally when i first set off.
i have checked and topped up the auto fluid and will probably drain and change it this weekend but has anyone any other ideas as to what it could be? i've heard there is a multi plug on the box that corrodes but not looked for it yet, could this cause these symptoms?

[J44EAG]

Welcome to the Club.

Corrosion and bad connections cause more problems with electronic glitches than anything else. Often taking plugs apart, cleaning and greasing with elecrical grease can effect a cure. Sometimes it is necessary to go further by way of electronic interogation. Many garages have an Autologic or similar piece of equipment which can act as a pointer to the problem you are experiencing.

I would clean up multiplugs first and see if you can fix the issue. After that, I think you might need some professional help.

However this is the first reply to your posting and other members looking at this post, may well be in a better position to help you further. As an owner of a modern S-type, I regret that I don not have first hand experience of malfunctions on your Jaguar model but I hope the above might just give you an initial starting point.

I would add that a visit to a good auto transmission company for their advice would not be time wasted. Most will have seen your problem many times before and be in a position to advise more precisely than I am able.

Hope this is of some assistance. Keep an eye on your posting over the next few days. One of our other members is bound to be able to offer further opinion.

Kind regards.

Mike Kennedy. S-type Coordinator JEC.

[robv12]

The 40 ZF box is usually bullet proof, what you have here as you correctly assume is the limp home mode

I would change the oil and filter, an easy job for a competent diy man, unlike v8 cars, while under there locate the multi pin plug, left hand side behind the sound deadening, remove and clean

Finally, while doing this have the battery disconnected, when you are done, reconnect, having noted your radio code and not leaving the keys in the ignition, 40 has a habit of locking itself when you reconnect, this will dump the error from the cars memory and that should be the end of your trans light coming on

[chuggernought]

thanks for the info, changing fluids and servicing no prob, i was a professional mechanic then on to roadside breakdown and recovery until a couple of years ago when ill health forced me out of the trade. i am also a classic land rover enthusiast(i have 7!) just not done much work on jags before so learning curve time.
radio code not a prob as it was already lost when i bought the car! thats another story haven't had chance to whip it out and have a look yet theirs certainly no sticker under the bonnet so i presume its dealer or decoding time.

[robv12]

how did you get on with sorting you problem

radio decodes can be done by email with DND services in Torquay, I use them for all mine when needed

[chuggernought]

hi mate, still got the annoying light, i have changed the autobox oil and filter and disconnected/ cleaned the multi plug, although it was in pretty good nic, disconnected the battery for 30 mins. the box is still going into limp home mode after about 10 miles but fine until then, i'm convinced its an electronic glitch rather than a box fault as it drives so well until warmed up, if i turn the engine off when warm and restart it the light stays off for only about a min before coming on again and back into limp mode it really seems like its temp dependent.
is there a diagnostic socket for the gearbox on these cars or is there an easy way of getting the actual fault code from the box? must get hold of a workshop manual!
have to say it still drives well in limp mode just a bit sluggish as it pulls away from a stand still and a hell of a bang when reverse selected, smooth as silk when the lights not on.

[robv12]

ok, you may well have a fault in the TCM, located in the boot,(I think on your car, if not in the left hand footwell under the dash), these can suffer with age and damp, very often a dodgy joint cause a fault, my own V12 had the same issue some years ago, just a dry joint on the output speed sensor circuit, could have been expensive, but my local TV repair man redid the joint and all has been well for years now

[chuggernought]

at last sorted the annoying gearbox light! found the tcm as robv12 said under the passenger dashboard behind various other control units, noticed a dribble of rust on the metal carrier above it but unit looked fine, after disconnecting the battery whipped it out and took it to bits to find a nice inch round blob of rust on the circuit board and componants where water had pooled after leaking in.
cleaned it all up and drenched the whole lot with switch cleaner, left to dry and refitted, then checked the throttle pot connector under the bonnet and gave that a good drenching with switch cleaner too.
reconnected the battery to find gearbox light now on all the time!!! alot of swearing and thinking "thats done it now i've made it worse" but after about 20 miles driving the warning light blinked out and now all is well stays out permanently. i think the newly reset tcm had to "relearn" the gearbox and it took some milage to do it.
so hope this post helps others with this all to common fault, now enjoying the squirty sport mode on the gearbox again!
thanks for all the help.

[chuggernought]

at last sorted the annoying gearbox light! found the tcm as robv12 said under the passenger dashboard behind various other control units, noticed a dribble of rust on the metal carrier above it but unit looked fine, after disconnecting the battery whipped it out and took it to bits to find a nice inch round blob of rust on the circuit board and componants where water had pooled after leaking in.
cleaned it all up and drenched the whole lot with switch cleaner, left to dry and refitted, then checked the throttle pot connector under the bonnet and gave that a good drenching with switch cleaner too.
reconnected the battery to find gearbox light now on all the time!!! alot of swearing and thinking "thats done it now i've made it worse" but after about 20 miles driving the warning light blinked out and now all is well stays out permanently. i think the newly reset tcm had to "relearn" the gearbox and it took some milage to do it.
so hope this post helps others with this all to common fault, now enjoying the squirty sport mode on the gearbox again!
thanks for all the help.

[chuggernought]

ooops, got a message saying it could not post so posted it again, the server must be telling me porkies!