Hit the park switch and……”Parking Brake Service Required” Arggh!! I’ve been there, don’t panic, this is what you’ll need to do.
EPB won’t release? The EPB is a common feature on many late model cars. They are electro-mechanical devices employed to apply and release the parking brake. Releasing the stuck brake will require removing the wheels, EPB motor, and unwinding the brake caliper. 6 common causes of EPB failing to release include:
- Blown fuse
- Faulty EPB motor
- Faulty EPB wiring
- Faulty EPB switch
- Faulty EPB sensor
- Faulty EPB controller
In this post, you’ll learn all the most common causes of EPB faults, how to diagnose your EPB fault and what you can do to release your brake right now.
Overview Of The EPB
You already know what the EPB (Electronic Parking Brake) does. I prefer the old style pull the handle brake on/off. They rarely leave you stranded as the EPB will. Not to worry, we’ll get it figured out.
In most cases of EPB failure, the root cause is a faulty rear caliper motor (actuator). The typical setup is a bolt-on actuator for each of the rear brake calipers, although some calipers integrate the motors and some systems use just one actuator.
The typical system comprises of:
- On/off switch
- Control module
- Two rear brake caliper actuators/one actuator and cables
- Brake position sensor
How does it work?
This is a brief explanation. The EPB dash-mounted switch sends a parking brake ON/Off signal to the electronic parking brake module (EPBM) by way of ref voltage drop. The EPBM, aka controller, processes the request and sends a ground and power supply to the brake actuator(s) (motor).
The actuator (motor) on each of the rear calipers turns a spindle screw at the rear of the caliper, which pushes the pistons and pads against the rotor. The parking brake remains on until commanded off.
The single actuator type EPB is a little different in that a single actuator pulls two cables attached to rear caliper parking brake levers. The effect is the same. The rear caliper pistons and pads are held against the rotors.
How To Release The EPB
As you know, by far, the most common EPB faults are failed rear actuators. However, we won’t know that’s your problem for sure without going through a few tests. More on that later. But for now, I’m guessing your priority is releasing the brake.
Releasing the EPB isn’t a five-minute job, unfortunately. There are a few different ways to approach releasing the brake depending on which component has failed, and of course, you won’t know that without a scan tool or some detective work, and as promised, we’ll get to that later.
For now, let’s assume you don’t have a scan tool to hand. We’ll approach this old school.
You may find the brake resources page useful, it’s a fluff-free guide to DIY brake repairs.
Here’s the fastest route to getting your vehicle moving without a tow truck. When the EPB switch is pressed, do you hear the motors running? If you do, it increases the chances of a single failed actuator. Jacking each of the rear wheels in turn with the EPB off will isolate the failed motor (assuming you have two motors fitted).
If there’s no noise at all when the EPB is pressed, this leans towards an on/off switch or controller issue, meaning we may need to release both rear wheels manually.
Begin by checking the following:
- Function – Many EPB won’t release unless certain procedures are followed. Your EPB may be auto or manual, make sure you are following correct procedure. Check your drivers manual. Many EPB’s won’t release unless foot brake on, door closed, seat belt on etc.
- Check fuse – Your EPB will be listed in the fuse box or in the drivers manual. Check the fuse is Good and the correct size.
- Visual – Check the rear actuator wiring connectors are in place. Damaged loose or disconnected plugs are common. Give them a wiggle, and have a helper actuate the button.
After running these checks, we’ll now need to access the actuator. Jacking the vehicle and removing the wheel may be necessary. Use axle stands to support the vehicle.
Tools – A power probe would make life really easy, but you can MacGyver up some jumper cables and wire with shielded probes. You could also use a small household 9v battery. We’ll be attempting to release the motors (if working) by hot wiring them.
Removing The Actuator
If the hot wiring doesn’t work, it means your actuator is faulty and will need to be removed to release the brake. Most actuators will likely be bolted to the caliper using a couple of Torx heads. Remove the wiring harness, actuator securing screws, and remove the actuator.
Removing the actuator reveals the rear of the caliper piston and actuator spindle. Use a Torx etc., to turn the spindle. A rear caliper is normally retracted by turning the piston clockwise and pushing. However, as we’re working on the reverse side of the caliper, turn it anti-clockwise.
Turn a little and check if the piston starts to retract. If not, try the inverse to get things moving.
Now free to move the vehicle to a suitable location for repair.
How To Check Fuse
The fuse is the first and easiest check to make. Start by pulling the fuse, check the element, and check the terminals for fretting (micro arching). Replace the fuse to be sure and check the correct rating. I never assume the removed fuse is the correct size. Always check the driver’s manual or fuse cover.
How To Check EPB Switch
The On/Off switch/button gets a ton of action and is No 2 on our list of failures after the low hanging fruit such as fuses etc. The switch is not hard-wired to the actuators as the EPB switch simply signals the controller its requests for brake on or off.
The switch employs a 5v reference which the controller measures constantly. As the on or off switch is activated, the voltage changes, which is the signal to the controller to take action. Testing the button is easy with a scan tool as the tool feeds you with live voltage readings as seen by the brake controller.
Pressing the switch and checking for voltage change indicates the switch is functioning. Without the scan tool, we’ll need to access the button-out put wiring and check for voltage change as the button has activated both ways.
How To Check Controller
Using the scan tool obviously will make life a ton easier. No communication with the controller is a symptom of failure. However, a CAN wiring issue or another faulty controller could also be the root cause. As a mechanic, I’ve been trained not to concern myself with the inner workings of a control module. Verifying a good power source, ground, and solid inputs, the outputs can be measured. No outputs mean the controller is faulty.
Misunderstanding all the inputs required to produce an output can lead to misdiagnoses, and controllers aren’t cheap. A good quality scan tool helps, check out the scan tool I recommend here on the “Mechanics tools page”, or check out the Amazon link below.Amazon Scan Tool
How To Check The Actuators
The actuators can be tested in various ways. The scan tool is the best starting point. Using a scan tool, as you know, allows you to see what the brake controller sees. This turbocharges the whole process of fault-finding.
Check voltage at the plug connector. Back probing works better than removing the terminal.
Use a DVOM to check resistance across the two motor terminals. An “OL” reading indicates an open winding, meaning a faulty motor. Similarly, a resistance valve below 10k suggests a short in the motor. Applying power and ground to the actuator is also a useful test or run.
Wiring faults are common too, and you won’t be surprised to know the scan tool makes this type of work actually enjoyable. The scan tool sees what the controller sees. So, for example, you can see the request coming into the controller from the EPB switch and can see the command going out.
With this type of info, you know the switch is good, the controller is good, the problem is either wiring between the controller and actuator or the actuator. Testing the actuator and finding it good would therefore show you the fault lay in the wiring between the controller and actuator.
Doing this work without the scanner means time and effort gaining access looking up wiring diagrams etc., not quite as much fun. The old-school way works too. Using the volt drop method will eventually get you to where you need to be. Check out volt drop testing at the end of this post “Car won’t start but lights come on.”
What happens to the parking brake when the battery dies? When the car battery is flat, the Electronic Parking Brake Remains on. To release the brake, charge the battery or use boost cables connected to another battery.
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John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write fluff-free articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.