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Thread: Cruise control not working after master brake cylinder replacement

  1. #1
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    Cruise control not working after master brake cylinder replacement

    Hi all,

    First post on forum; be gentle!

    After replacing the master brake cylinder (facelift version with sensor) in the Autumn, when driving, the cruise control does not engage (work) at all. There are initially no warnings. After a few miles - usually after reaching a higher speed/revs the "parking brake fault + cruise not available" warnings appear. The warnings do not extinguish until the ignition is re-started. The two brake pedal switches seem ok and the epb has been properly calibrated, also, no obvious OBD fault codes show up. Really grateful for any ideas.


    2005 S-Type (facelift) sport 3.0 V6

  2. #2
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    On closer inspection, I discovered that the two brake pedal switches were not OK. The upper (green) switch should be normally closed. If this is not working correctly, "parking brake fault" will be displayed and the car will lock in park. (NB anyone wondering why they have a "park brake fault" when their park brake module/actuator test ok) The lower (white/blue) switch has a normally open action, if this switch is not working correctly, the cruise will not work and (as in my case) a "park brake fault" may show up after driving. The cure was to physically re-calibrate the two switches. This is done by simply removing the switches with a twisting action and re-inserting the switches with the brake pedal in the rest (not applied) position. The switches have an ingenious self calibration ratchet mechanism that resets when the switch is twisted back into place. There should have been no need to re-calibrate the switches as nothing new was added or taken away from the braking system, but nevertheless, this simple fix was all that was required after months of head-scratching

  3. #3
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    Very useful post and glad you got it sorted. I would think that when you replaced the master cylinder the linkage has moved out of its normal range of travel,causing the switches to lock out. This may well be a designed in fail safe feature of the cruise or ABS or just another path on the Jaguar magical mystery electrical trail. God knows I have been down enough of them back in the days of XJS ownership.
    2002 52 Plate 2.5 Manual With a few toys.

  4. #4
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    Hi Tricky. Yes, in theory, the travel should still have been the same. (The cylinder was simply removed, inspected cleaned up and replaced.) Obviously though, the travel had changed as the lower (cruise) switch needed resetting. This leads me to point out that occasionally this reset may be needed even if the cylinder has NOT been removed. As I pointed out before - the top green (brake light) switch not being properly adjusted could cause a nightmare, as open circuit on this contactor leads to "park brake fault" and car LOCKED IN PARK! On my search for an answer to this problem, the number of "Locked in park" posts was staggering. Anyone getting "park brake fault" with good park brake module and actuator should learn the simple way to adjust the brake switches before investigating anything further. Testing continuity/correct function with the switches in place is really difficult due to their location. When removing the switches, beware that they do not test correctly on a continuity checker unless the collar of the switch is rotated the same as if locked in their operational position.
    Last edited by Floodlightfloor; 03-04-13 at 14:00.

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