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· Registered
36 Posts
Discussion Starter · #1 ·
2004 Disco, auto tranny.

It stopped working around the time I started having problems with the gear selector switch (code P0705). I pulled and cleaned the selector switch and it works fine now but I still have no cruise control. Not sure if the two are related or if it was a coincidence.

There are no check engine light codes
There are no vacuum lines from brake pedal. The unit is electrical.
The vacuum line between the actuator and the pump is good
The vacuum pump assembly holds vacuum
All my fuses are good
All my brake lights are good
My brake pedal switch is good
My gear selector switch is good
My cruise control master dash switch lights up
Horn works

What now?

· Registered
380 Posts
This thread on talks about a fix with a stuck valve, maybe you should look into it, if you pull it and try blowing air through it and no air goes through, this could be your problem. Ill try and find the original post and not the quoted post, if that means anything.

QUOTED POST: Cruise Control Vacuum Pump Fixed! Brilliant Repair - DiscoWeb Message Boards


· certified idiot
694 Posts
even though the selector switch is clean and working if the dash display does not show a D when in drive then the cruise control wont work. It may be selecting D fine but if its not displaying it then the ecu cant necessarily see it and the cruise wont work. Check you have it set properly from when you installed it. Common problem on the later xj6 jaguars which have the same autobox - they are very sensitive to the gear selector switch being set up exactly right.

· Registered
36 Posts
Discussion Starter · #4 ·
Thanks to those who tried.

I figured it out and posted a pic for those who might have the same problem.

The main pump motor was seized.

There are 3 electric motor windings in the pump housing.

Pop off the plastic cover that has one vacuum line on it and a clear/white silicone ring seal.

Behind that is a white plastic molding with an electric winding attached to it.

Disconnect the two wire leads from that motor that attach to the back of the pump assembly's harness plug. Be sure to reference the leads for reassembly as they are not marked "positive" and "negative".

Remove white plastic molding with motor winding.

Look at the picture. At the end of the main motor shaft there is an offset captured ball bearing that has a black plastic arm molded around it. That plastic arm is connected to a plunger that creates the vacuum for the actuator on the cruise throttle cable. That bearing was lightly rusted and very slightly seized. It took very little effort for me to break the bearing free which tells me the motor has very little torque since all it has to move is a small, lightly fixed, plastic plunger. That means that it takes very little to stop this motor

I sprayed white lithium grease in the bearing for good measure. Not sure if that is the best stuff to use in this situation but its what I had available. If you use anything with petroleum products in it try to keep it off the plastic parts.

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