Does Jaguar publish the specs for bench testing the subject switch P/N LNB6420BB? I've been experiencing the Failsafe Engine Mode warning (DTC P1571) with concurrent loss of cruise control. The fault doesn't trip if I drive with the cruise control disabled. I've had the switch out and appear to get a much higher resistance on the center two pins than the outer two when the two small push button switches are depressed. Suggestions?

 

I don't think there should be significant resistance. It sounds like time to replace the micro switches or the whole thing. There was a thread on this or the XK8 forum yesterday, I think, in which one of the members described the micro switches.

 

These switches are SWITCHES! I guess you found the problem.

 

You will find a TSB on the switch.

I would replace it -- they are not expensive.

 

IIRC, and it has been awhile, there are two identical microswitches in that assembly. In my case, one of them was "lazy" when opening and closing. Using a soldering iron, I swapped them and the problem went away.

I think one is used for the brake lights and the other goes to the cruise. It should be in the schematic documentation.

-Mike

 

Just ordered a replacement switch assembly. Hopefully that corrects the problem? Or at least I'll have something to compare resistances. As an aside I've noticed, since I turned off the cruise control, my passenger side mirror no longer drives into the lower stop whenever I used the key fob to unlock the doors. Maybe the new switch will fix that too!

 

Well, you did not say how much higher resistance one switch read from the other, but if either is reading more than 4 to 8 ohms, you have a bad switch.

 

The 2 microswitches work opposite to each other.


The one for the brake lights, makes a circuit when the pedal is pressed, the one for the cruise, breaks the circuit when the pedal is pressed.