Hi,

I have a 1992 xjs 4.0. I've just started to use this month after winterizing. For the first time I took her out in the wet afterb she had been washed.

The gearbox faultlight has come up on the dash and she will not shift up. I turn her off and restart and everything is back to normal but this has happened a lot since yesterday.

Can anyone please advise?

All the best,

Zarathustra.

 

Have you checked the level of your transmission fluid?

When was the last time you replaced this transmission fluid?

 

Last time I checked last year it was bright red. Hardly done any mileage since.

I'm not sure how to check the level when cold. Can you please advise?

Thabks.

 

Zarathustra,

You need to check the fluid level with the engine running, when it's fully warmed and fully cycled through all the gear positions. Then immediately check it with engine still running.

There is a strong likelihood that the issue is not with the gearbox itself. The car just puts itself into Limp mode to protect the car when it identifies a problem elsewhere, such as the MAF etc.

I'm guessing you can't get someone to read the fault codes that have been thrown? Have you got a trip computer in your car?

Paul

 

THanks Paul. Could a weak battery cause any issues? Do you know where the obd port usually is? Mine is a 1992 4.0 cab. I will check atf level. I have read the handbook and need to take it for a 15mile spin before checking.

All the best,

Zarathustra.

 

A weak batttery can cause this. If the voltage drops too much when starting it will casue the TCM to panic. Fully charge the battery and have it load tested.

 

A low battery voltage can definitely cause spurious fault codes. But as you seemt o imply that it's throwing the code after running for a while, rather than on immediate startup, then maybe that isn't the cause? What battery voltage do you have immediately prior to starting?

As you have a 92 Convertible (not a Cabriolet, that's quite a different car!), then you don't have an OBDII port. Your car requires a dedicated Jaguar PDU system or clone, to read the codes. However, you can see them if you have a trip computer fitted in your car. Do you have that, or just the standard clock?

A 15-mile drive will be fine, but you can fully warm the car at rest and repeatedly cycle the gearbox multiple times, and you'll get a pretty good reading. My money is still on it not being the gearbox itself.

Cheers

Paul

 

Hi everyone,

I've checked the gearbox oil and it's all good.

I have a 1992 cabriolet. The voltage just before starting is less than 13v approx 10v. Once started, the voltage is greater than 13v.

I've tried another battery from another car 550cca, 62ah. Not sure battery is the best. Happened again with the replacement battery. Transmission light came on after 7 miles. Switched off and on and was okay again. I'm now trying another battery 500cca, 60ah.

All this happened after I cleaned the car and thoroughly wet underneath rear wheel arches and also drove in rain. Not sure if this has anything to do with it.

All the best,

Viraf.

 

Viraf,

Those readings don't sound right. Your car just wouldn't start if the voltage was 10v. Also at a high idle, the voltage as measure either at the bulkhead terminals or directly at the battery should be about 14.1v. I would try with another multimeter.

Start with a battery that registers 12.5v+ before the ignition is on. Once started, the voltage should be 14.0v+ at a fast idle. If not, the alternator / belt is suspect.

As mentioned, you don't have a "Cabriolet", you have a "Convertible". That's important if you need to buy alternator / battery etc.

Cheers

Paul

 

Thanks Paul. I'll check all that. I do think I have a computer as where the clock is sometimes codes appear before starting.

All the best,

Zarathushtra.

 

We still don't know whether you have a trip computer or clock?

I'm not aware of a situation where a low battery caused transmission faults....it's plausible, but not common?

I had an issue where one of the solenoids on my valve body was being reported as bad (by transmission code). This is for a 1996 with the ZF 4HP24 transmission. My shop said he could replace the solenoid without guaranteeing that was the cause, or for the same amount of money swap it out with a valve body from a parts car...and a warranty. (I think it was 3 month warranty) That is the way I went. I do still have the valve body with the "bad solenoid".

Not sure why I'm telling you this, but I thought it might be useful down the road. The shop was a jag specialist, that's why he happened to have a used part for me.

 

Ah, this makes all the difference as you obviously have the trip computer fitted. What fault codes are appearing?


Four years ago, my alternator failed. As the battery voltage dropped, it put the car into Limp mode, and the car eventually stopped on a long hill. Presumably the conflicting low voltage readings caused the ecu to get confused, and it uses Limp mode to protect the car.

However, as you're able to constantly restart the car, I'm not convinced yet that you've got a voltage problem.

Paul

 

Paul,

No fault codes appearing. Only thing that happens in transmission light on dash and car goes into Limp mode. After switching off and leaving for a minute and starting all back to normal.

Voltmeter in car is bang on 13v with car running. Will check with voltmeter as per your advise soon hopefully.

Thanks for all your help, any more advise would be much appreciated.

Zarathushtra.

p.s the same happened to me last year ie battery would not charge after I'd not replaced terminals tightly. My car died too. Voltmeter would show below 13v and drop to zero ie battery would not charge. I would charge the battery and the alternator would not charge it once in and it would drain to zero again. Was told by AA alternator. I disconnected battery and charged it. Left car over weekend, my logic being things would reset. Connected battery and everything worked perfectly from there onwards.

 

Viraf,

A bit confused as you said above that you had codes appearing before starting?

Paul

 

Hi Paul,

Sorry I should have been clearer. I've had codes appear in the past. No codes appear relating to this issue. In fact no codes appearing at all at present.

All the best,

Viraf.(Zarathushtra)

 

anymore advise please? I'm baffled and quite upset with this fault.

 

What's the battery situation? Do you now have a fully charged battery ready to start the car?

Paul

 

I've tried 3 different charged batteries. Problem persists.

 

So we have Transmission limp mode with no code on the trip computer?

There has to be a shop with a PDU that can pull the code for you? I'm just not confident that anyone will be able to remotely troubleshoot your issue for you?

Longshot attempt to throw money at it could be:
1. Replace the transmission ECU, Should be easy to find on eBay.
2. Flush and replace the transmission fluid

That's all I got.

 

What is the voltage of the battery immediately prior to startup? And what is the voltage of the battery at fast idle (1200 rpm) immediately after startup? It will be helpful if you can take voltage and the efficiency of the alternator out of the equation.

Paul