Out of the blue about 8 months ago, I stopped the car (base not R), turned it off and got "cannot apply parkbrake" Turned the car back on, then off and yellow warning went away.


Recently it has started to occur with a touch more frequency. I will turn the car on and either immediately or within 5-8 seconds, I get "parkbrake fault" with yellow warning. I can stop the car and even with the warning still use the switch and engage and disengage the parking brake. This might happen every 10-15 starts.


Other times i can stop the car and put in park and will get "cannot apply" or "parkbrake fault". I turn off, turn on, turn of and gone for the next 12-15 stops (these are guesses as to the amount of starts and stop, but a good estimate.


Within the last 3 weeks I got a new AGM battery and reads, as I write this, at 12.9 volts when off. I had been getting the flash of cruise not available and then the abs and dtc lights were staying on a little longer and knew after 3 years in Texas- that it was in the dying mode (would read usually about 11.8-12 volts and I know that 12.6 seems to be a sweet spot).


So battery is fine. I have never ever had any trouble engaging the park brake while driving or when the car is turning off (except at the exact time I get the parkbrake or cannot apply faults)- although even when the yellow warning appears- I can still manually engage and disengage the parking brake- it just won't do it automatically.


Two weeks ago, I changed my pads and rotors (as a side note the Hella Pagid pads i put on seem to the best I have ever used- but that is for another discussion).


I followed the procedures for resetting the parking brake as outlined in TSB S206-04 (Electronic Park Brake (EPB) - Re-Calibration Procedure).



Parking brake works fine, next to no noise, except for the slight sound of movement of the rear brakes and what sound there is to the PB motor when sitting in the car.


I had checked the rear calipers as I screwed them back in, properly lubricated everything I could find on the park brake system- from lines to springs to parking brake lever, ect.


I was still getting the occasional fault.


So i disconnected the battery today and unhooked the 2 wire connectors to the PB module, there was no indication of any moisture, but cleaned them anyway with CRC Lubricant and Corrosion Inhibitor for electronics. Put them back, connected battery and did the proper re-calibration of the EPB.


Drove the car about 25 miles made 3 stops and when T started the forth time got "parkbrake" fault again which was once again rectified by turning the car off and back on.


It is a bother and nuisance and so far has not caused me any problems nor have I got a flashing red light or warning.


This is the TSB for the diagnostics and i have essentially done most of this.


http://www.alldatadiy.com/alldatadiy...2914/138775737




So what gives and does anyone have a suggestion. There is no indication of any moisture or the like in the trunk. I have heard there is a relay inside the actual module that can be replaced- does anyone know? Is there any sense to opening the module- if that can be done and spray with my electronics cleaner?



This really sounds like the PB module is not getting power at certain times- if only for a moment, but only at stop and start- but then that is just a guess. I actually care very little for even using the PB as i have a very flat garage that if I put the car in neutral- it would not go anywhere.


Help and comments are highly appreciated.


Tom in Dallas/Plano
05 S-type 3.0 103,000

 

I'm not sure we know for sure but the best start would be whatever codes are in the EPB module.

E.g. it may be finding it's drawing too much current. If so, it would be one of (however many) possibilities.

Etc - depending on the code(s).

 

A friend had a scanner that would read the codes other than the P ones and in the PB module- the only code I had was related, after research, for it to be calibrated and that was after I had changed the brakes. Erased it and has not come back. I had no codes related to short or open circuit, lack of power or anything of that nature-which I semi-expected to see.. Would not I blow a fuse if it were drawing too much power??


Or could this just be a stubborn relay inside the module itself?



Thanks


Tom

 

Are you sure it's seeing any codes that are there? It's disappointing if the EPB can detect and report a problem yet not set any codes at all.

I think you'd only expect a fuse to blow if it took more current than the module can handle.

I expect the module monitors the current the motor draws. The module can switch the current on or off (and possibly can vary the amount). Now, a motor draws more if it stalls or moves slower than expected and I expect that is what the module sees and reports.

You could measure the current through the motor (and module) using a meter (in the fat wires to the motor). If the motor is turning OK for a while but then stalls you'd see the current rise at the point it stalls.

The module also probably knows the max time it takes a working motor to open/close the brake fully, i.e. the time by which it should have already seen a stall (current rise). It may be that the error is when that time is exceeded.

A motor which is badly lubricated might draw too much or stall after the wrong time. Similarly, (Bowden) cables that don't move freely will affect the current through the motor and the time taken to fully open/close the brake.

Unfortunately the motor is very awkward to get at and the cables look a swine to replace.

 

Good info to think about and what you are describing is in part the actions of a runaway relay. My only issue is one of the various points the parkbrake fault will come on. I start the car, back out of the driveway- drive 50 feet- it pops on (no action of the parkbrake is taking place at that point) Stop the car, turn engine off and on and now good to go. This has occurred when I have not even allowed the parkbrake to set the last time I stopped the car (holding down the switch while turning off). I have also had it switch on when I come into the garage and even while I am putting the gear in Park and before I have turned off the engine.
It made me think that perhaps with the gearshift and the switch- something weird was happening, but looking at the diagrams that does not seem to add up.


From my ears I have never heard the motor stop or stall and have always had smooth sounding parkbrake engagement.
The calipers seem fine, but could this be an issue, since I can really only look at them when not against the pads and rotors. Never had one ounce of dragging or any indication in any way that the parkbrake was not retracting. If I apply the parkbrake while driving- I get a very smooth stop with neither wheel being dominant.




Thanks


Tom

 

My TheoryDuJour(tm):

The ignition switch is intermittent. Either it's not springing back 100% from Start to the Run position, or the internal contacts have high resistance.

A couple of quick things you can do in post #95 here:


https://www.jaguarforums.com/forum/s...5/#post1847363


Another thought is to check where the battery ground cable is attached to the body. The final fix may not be one big slam dunk. It may be a matter of small incremental fixes.

 

Interesting. I will ponder that and see if jiggling does anything.


The battery is attached to the body quite fine. I checked that when I was unplugging and re-plugging the PB module.


Tom

 

Don't be afraid to run the second test, too, the one with a meter. Even if you don't fully understand the concept of a voltage drop test, such a test is amazing. I've encountered a lot of people who don't get how it works, so they never run the test. In the end, they cause themselves extra grief. In maybe five minutes tops, you can determine if the switch is capable of carrying adequate current for the circuit in question.

I've diagnosed and fixed a lot of mysterious electrical faults with that test. For the EPB faults cropping up on later models, I think a marginal ignition switch is a likely part of the equation:

1) Moving parts are far more likely to fail than fixed connections or solid-state components. Such failures are not often 100%, but more commonly a slow degradation.

2) The DSC and cruise control also get power through that same branch of the multi-pole ignition switch. Those faults are commonly seen at the same time as the parking brake fault. That's one of the biggest clues.

Based on forum experience, the EPB (and DSC/cruise) seem to be the most sensitive of all systems to low voltage at engine start. I think of them as the canary in a coal mine, chirping out a low-voltage warning none of the other systems can see yet. Unfortunately, instead of clearly stating "low voltage" for all to understand, you just get some generic inop messages instead.

The trick seems to be how to interpret them. I'd suggest an EPB message by itself would point to an actual EPB fault such as a binding cable, worn motor, etc. If combined with a cruise control (and optional DSC) message, you're probably looking at a low voltage input.

For the multiple message scenario, we've had good results simply replacing the battery. With high electrical loads, these cars are tough on batteries. You've already replaced yours, yet the fault continues. That's why I'm leaning towards a problem with the ignition switch. I need you to be the guinea pig and run that voltage drop test. It's a very simple test and you may be pleasantly surprised.

As an example, last summer my pickup was acting up. I traced the problem to marginally low pressure from the electric fuel pump. The power to the pump went through the ignition switch. A voltage drop test showed 0.9v drop through the switch, when the limit is 0.5, but ideally even lower. Understand the pump still ran, but just not at 100%. I replaced the ignition switch, retested the voltage drop to a much healthier 0.2v, and all was well again.

So if you would, please just humor me and run that test. I bet the hardest part will be removing the cover at the primary junction box.