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EPB (Electronic Parking Brake) actuator - works direct from battery


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As part of my continuing wrestle with EPB faults on my 2007 2.7 auto, I have a question to ask of anyone with such knowledge.

The EPB throws up the DTC C1785 "EPB Motor open circuit". I have tried a replacement module (of matching codes and revision number) with no change.

I have just replaced the 2 yr old battery with a Bosch S5 830 100Ah.

Initially, the EPB failed to release when I started the car but after some research on here I tried two wires direct from the battery to the green/white and red/white wires of the multi plug from the module and the Actuator released.  The Actuator will come on and off direct from the battery.

Does this mean that the actuator is Okay and that the open circuit lies somewhere else?

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I have resolved this issue now - it would appear to have been loose wiring or maybe damp in the boot area...not sure which but after drying out the boot and pushing all the EPB module connections in from the rear of their multi plugs, the EPB worked again. I don't know why this didn't work the first time I wiggled the wiring but I'm  just glad it's sorted now.

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 Hi as a new member  with some experience in the motor trade     AA patrol (ret ) 16 yrs   the handbrake is likely controlled by a relay and probably a fuse   a fuse is usually easy enough to find and replace ,   a relay is a little more complex   but terminals can  become corroded -  poor connection  (open circuit  ) or just burn out ..
 Finding the control relay  and testing  and or replacing it is  a good start to a permanent repair .

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Damp in the boot is a common problem, water usually leaks in above the rear lights and can cause lot of problems with electronics in the boot

the EPB is very sensitive to low batteries, so if the battery is low, first thing on cold mornings, battery voltage can drop causing problems with the EPB module, if voltage is low it goes out with a fault, which be reset by either disconnecting the battery or unplugging the epb module itself, same as disconnecting the battery but with out the pain of putting radio code in and resetting all windows.

most common faults are stiff cables, stiff calipers or worn epb motor/gear inside and sometime fail epb reed switch, the park brake is quite complicated how it works, it monitors voltage and current of the motor moving in both ways, it gets pulses as it moves, so when you calibrate it after disconnecting the battery it learns, brake on position and brake off position, learns how long it took to get there and how much load it took, so if any of these change significantly it brings a fault up, most commonly cause by low battery voltages

if you plug in with Jaguar IDS/SDD it talks to all the modules on the car, checking the EPB module with give you a fault code and reason of the fault.

you can also manually operate the epb motor if you handy with car electricals, have a look here https://www.youtube.com/watch?v=8xebdRYwtjE



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After I start the car I release the EPB by using the cabin switch and before putting into gear. When parking I'll place it into park then activate the EPB before turning off the engine. I just hate error codes.

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Many thanks for the responses and sound advice.  The fault  DTC C1785 has returned.

Each day when I go to start the car I get the same C1785 DTC. Today, wiggling wires and removing/replacing epb plus did not cure it.

I have removed, checked and cleaned all fuses relating the the Parking Brake but not relays. I'll check those too.

Dam - yes there has been damp in the boot recently (now dried out) but I believe that was from leaking water/ coolant top up bottles I kept in the boot. However, I will monitor to see if any of this abundance of rain is finding a way in.

The battery (a one week old Bosch S5) is reading 12.65v.

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c1785 is drive unit open circuit

so the wiring tp the park brake motor is open circuit, so worth checking the wiring, could be the connectors to the epb corroded, they wires are also known to snap by the park brake motor if there left hanging and not tied down, you swapped the module so that eliminates that

it could also be worn brushes on the epb motor, try tapping the motor, if it start to work for a while , could be brushes, worth testing at the module on the motor wires and see what resistance you get, if it fluctuates when you wriggle the wires by the motors, its the wires




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Hi Joe, Many thanks for the advice.  I am able to eliminate EPB actuator as being faulty because the actuator works both on and off when connected direct to the battery (connecting to red/white and green/white wires of left side EPB Module multi-plug)This also suggests no wiring issues between the Module plug (black - on left) that takes power down under the car to the actuator.

It appears to be sorted (for the moment at least) after tightening up the female side of the pin plugs within the module connectors - maybe they had become slightly loose with the numerous plug ins and plug outs when testing the actuator last year - damp may also be a contributor but all dry now.

I will update this thread after a few days if it is still okay - or sooner if it starts the open circuit C1785 code again!!


Many thanks



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  • 2 weeks later...

After continuing EPB problems and DTC C1785, I managed to detach the actuator connector CA269 and test the resistance between pins 1 and 6 (as stated in the Manual)

The resistance readings should be 0.1 to 0.2 ohms but I'm getting the continual 1 on the left side of the screen showing resistance out of range, ie open circuit (on any Digital Multimeter resistance setting) . I have now purchased a brand new Actuator and will update again once fitted. Fingers crossed.

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Brand new actuator fitted. All has been fine for the last 2 days. It appears the problem if finally sorted. HOORAY!!!!!!


I bought the brand new, genuine Jaguar EPB  actuator from Roger Young Ltd for £255 including VAT and delivery (UK)

They do state that this part will need to be encoded to your car. This information apparently comes from Jaguar. I have not had this problem and the new actuator worked instantly. All I needed to do was press the foot brake and hold it down whilst engaging the park brake switch (as you do to re calibrate after battery disconnect or new rear pads).

The label on the new actuator showed the same part number but different code and revision number to my original actuator, so it appears this isn't as critical as has been made out.

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Keith, Love your S type. Don't fall out.

You have the patients of a rock. I struggled to stay focused throughout your thread, let alone under a car trying to deal with the problem.

Maybe you can offer some in put to my thread " SCP Not Communicating"
, particularly to recommend an auto electrician with your level of patients..

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