This is where the rotary is in second gear.is this right?

 

don i checked the TPS and it read 3.7 ohms closed ,but did move steady up.does it need adjusting?i do have the idle screw a little low.

 

Did all the tests ,everything checked ok.light still on,have a feeling it's the TCU.

 

I wish I could remember. I posted a photo showing four different gear positions in my albums at Jag-Lovers, but currently only the thumbnail is visible and it's too small to read my labels. I just sent a message to the Jag-Lovers mods volunteering to help move my old photos over to the new server so maybe I can rectify this issue at some point.

The correct way to test the TPS is by backprobing the electrical connector and reading the voltage between the signal and ground wires. The Haynes Manual has the procedure if you don't have the Jaguar Workshop Manual. You can download a nearly-complete U.K. edition of the Haynes Manual here:

Haynes Jaguar XJ40 Repair Manual


It's easy enough to open up the TCM and check the circuit boards for cold/starved/cracked solder joints or water ingress.

Cheers,

Don

 

so it looks like 6 solder points and 2 diodes are fried in TCM

 

You have found the cause of your transmission warning lamp!

Now, what caused the diodes to fry?

 

Looks like water leak

 

ok guys no ims really confused,looked up TCM for the car and i found 5 different ones.do i need to get the same number that came out?

 

ok guys so im's really confused,looked up TCM for the car and i found 5 different ones.do i need to get the same number that came out?

 

Add the VIN to your signature, the year is not really of much help when sourcing part numbers.

Larry

 

1991 xj40 sovereign
maroon red Vin 640582
130720 miles

 

Ok well it looks like the part number you need is LMA2400AA but check for yourself here ... (this is the part for trans part number Gearbox-EBC3541)

https://www.jaguarclassicparts.com/u...control-module

These are pricey suckers so I'd check around your local wreckers for a used one or repair the old one (pick up the diodes, reflow solder etc)

Larry

 

car is going to the shop this weekend the module did not fix the problem

 

At this point, if I were you, I'd whip off the fuse boxes and check for dry or cracked joints. Maybe even reflow the joints for good measure?

Fuse boxes are a known weak point in these cars. When multiple and especially intermittent issues arise, the fuse boxes are definitely a consideration - which I doubt the "shop" will check.

Larry

 

What should the voltage be at the neutral safety switch? My mechanic says he's getting one volt

 

Why is your mechanic checking the neutral safety switch? Has something changed? If the starter cranks and the engine starts with the gearshift lever in Park or Neutral, your neutral safety switch is probably operating properly.

Cheers,

Don

 

He's checking everything associated with the transmission to try and find the problem limp mode

 

Is he following John Ping's diagnostic routine that I linked to in post #38? It has worked for me everytime I have needed it.

Since you had evidence of water in the TCM, have you also checked the ECM and CPU for water damage?

Off the top of my head, a malfunction of the Park-Neutral Safety Switch or Start Inhibit Switch will prevent the starter from cranking, but the switch is not otherwise connected to any of the transmission functions.

Cheers,

Don

 

One of the other websites is saying that the central microprocessor is back under the bird's nest what is the bird's nest and where is it? I'm getting close to blowing up my car

 

The Central Microprocessor, or CPU, is on the firewall/bulkhead just to the right of the center console/transmission tunnel. To get to it, you have to remove the passenger knee bolster and disconnect various things that are in the way, such as a panel on which relays or relay modules are mounted. The person on the other forum is calling all of these components that are in the way a "bird's nest." For the best access to the CPU, it helps to remove the glove box or passenger side airbag.

I have photos showing the CPU on our '93 but curently only the thumbnails are working:

Jaguar XJ40 Brains Behind the Dash

I can't remember if I posted the link to my TCM repair album:

Jaguar XJ40 Transmission Control Module Repair

Cheers,

Don