Autobox warning light flashes

[Clive]

I've had my first lovely Jag - a late 1992 XJ40 3.2 - for 3 months now with no problems. As a precaution all fluids and filters were renewed including the autobox. The box is the all electronic ZF 4HP 24E with a warning tell-tale in the instrument cluster. Only problem that I've had is this warning light flashing on under heavy, sharp braking, usually at low road speeds and with the box cold. Only stays on for about 1-2 seconds. I have Nigel Thorley's excellent Haynes XJ40 model history and he says that bad electrical connections and relays can cause the box to go into "limp home mode." But the problem I am having sounds like fluid surge or starvation if the box's pump sucks air for a moment which I have experienced with other autoboxes, usually when fuild is low. The guy who changed the fluid said it was very dirty and it is already brownish again on the dipstick but maybe it just needs another flush to get the muck out. Anyone had this problem and should I be worried?

[stefanantinaho]

Reading your story, one thing truck me, funny as it may sound, as I had the same thing happening on a previous car, a 4.0 Sov '93: the problem eventually was diagnosed as bad earth, caused by a seriously corroded earth-point on the fire-wall. Some little welding sorted the matter, nothing wrong with the 'box. And, as far as I know, the fluid surge should under no circumstances cause the light to come on, anyway.

A brown fluid is alway a wee bit worrying, as it indicates that the 'box may have been running very hot for some reason (usually low fluid level). But, at changing the fluid you only change a fraction of the total, so a lot of the old, dirty oil is always left in the 'box, mixing with the fresh oil.

[robv12]

i would check the multi pin connector on the side of the box where the loom attaches, these can corrade with time and give odd warnings on the dash, remove and give it a good clean, access is from under the car

[Clive]

Many thanks for both your replies. There probably is still a lot of muck in the box as you say. My car is solid but was probably a bit neglected when I bought it and had been a trade in at the garage where I bought it. So the last owner was had maybe not been too bothered about servicing if they were soon to part with the car. And the electrics giving false warnings is something I had heard about so I'm not too worried
Regards
Clive

[DEREK1951]

Clive, i beleive it could also be dirty contacts on the transmission power relay, which on my '93 model is the one with the purple base in the group of relays on the firewall , you would have to check which one applies to your model as i'm not familiar with yours, this was giving me the dreaded transmission warning light , coupled with limp home mode , i also changed the oil three times when i first got the car, but it still doesn't look as bright as fresh fluid and due to the way it remixes each time i don't think it ever will , but i know how much fresh oil is in there and i'm happy with it Derek...

[Clive]

Thanks to Derek 1951 for that info on the relay and the fluid condition. I can hear a relay clicking as the warning light flashes and we could well have the cause there. Possibly just fitting a new relay will cure it - I'll get one next time I'm at the Jagaur main agents. Sort of good to hear also that your fluid is still mucky but apparently will no ill effetcs!
Many thanks
Clive

[Clive]

Thanks again for all your ideas. This problem remains unresolved however. It definitely only occurs in wet conditions. This was brought home when pressure washing the car (including under the wheel arches) a couple of days ago immediately triggering the fault which had been absent all through the dry weather. So I took the car into my local garage to-day. Plan was to check the multiplug on the side of the box and then waterproof it using self-amalgamating tape. (I am assuming that this is the only electrical connector actually exposed to the elements - the under bonnet relays are nice and cosy and dry I would think.) Both I and the very experienced fitter looked for the plug but could not locate it. When I got home I double checked the location in the photo (page 7-10) in the Haynes manual but it was definitely not in that location on my car. I would like to get this sorted before the really foul weather sets in. Were there any variations in gearbox layout which could account for this?
Many thanks.
Clive.