Think Backwards When Working on Electronic Parking Brakes
Servicing Rear Brakes On Cars with Electronic Braking Systems
Today I would like to sharpen your minds about something that comes up quite often in our line of work. Rear brake pads, and more specifically, how to service them when there’s an electronic parking brake system on the vehicle.
The genesis of the idea for this article came from a Virtual Tech call I took on a 2018 Honda Accord. A sharp young tech wanted to do a rear pad slap on this vehicle and he wanted to know how to do it. The service manual was only of moderate help and he had additional questions. Turns out, so did I. So if you like hucking brake pads, have a seat and rub your brain against this whetstone.
Psst. There’s a free cheat sheet at the end of this article too
Quick Parking Brake Explanation
Electronic parking brakes have been around for quite a while now, and like skinning a cat, there are many different ways of accomplishing the same thing. Some manufacturers designed a cable that gets pulled on by a motor, but most companies put a small DC motor on the back of the brake caliper. As it’s the most common design, this is the style we’re covering today.
Electronic parking brake systems usually consists of 3 main components
- A control module of some sort. Sometimes this is the same unit that does the thinking or work for traction control and ABS, and sometimes it’s a bespoke unit just for the parking brake.
- A switch, to communicate the intent of the driver to engage or disengage the parking brake.
- Parking brake actuators. These are electronically-controlled calipers, and every system I’ve ever seen are on the rear of the vehicle. Sometimes they’re combined with the base brakes, sometimes they’re their own little sub caliper. Tesla comes to mind.
How Electronic Parking Brakes Operate
Now that we have an idea of the components, let’s talk about operation. Some manufacturers use the electronic parking brake every time the vehicle is shut off in park. Others use the parking brake only after a prescribed number of miles, to keep the caliper exercised. And still others use the parking brake as a hill-start assist, or as a brake-hold function every time the vehicle comes to a stop. Do a little research on the system you’re dealing with and try to get an idea about when you can expect the parking brake to be engaged.
My basic rule of thumb is to assume it’s always engaged unless you’re trucking down the road. We don’t know when the traction control module might want to turn on the parking brake, thus “always” seems as good a time as any.
Now let’s dive into the specifics.
2018 Honda Accord Electronic Parking Brake Components
The parking brake switch: pull up to apply, push down to release.
There are electric actuators mounted on the backs of both rear calipers—they have only 2 wires, one for power, one for ground. The Vehicle Stability Assist (VSA) module reverses polarity to engage or disengage the actuator. The VSA module judges the application based on how much amperage the actuator takes, very little amperage means the brakes are not applied, a lot of amperage means the pads are applied.
The Vehicle Stability Assist (VSA) Control Unit is in charge of the whole thing—the parking brake switch wires go right into it and the wires for the actuators come right out of it.
Now that I know the players, it’s time to get to know the game.
When does a 2018 Honda Accord engage the parking brake?
When the customer requests it, using the parking brake switch. Pull up to engage, push down to disengage.
Every 1,864 miles, if the parking brake has not been engaged, this is to exercise the calipers and compensate for brake pad wear.
Every time the ignition is turned off, depending on customer’s preference/settings.
When the Vehicle Stability Assist (VSA) system determines it requires increased braking effort in an emergency.
When the VSA system determines it’s unable to hydraulically apply pressure to the rear brakes during an ABS or traction event.
During automatic brake hold, if brake hold exceeds 10 minutes.
When does a 2018 Honda Accord disengage the parking brake?
Drive-away. Essentially, you start to drive with the parking brake engaged it will automatically disengage for you. How thoughtful.
Maintenance Mode. This is a service function you need to command with a scan tool, more on this later. The VSA module is supposed to retract the electric parking brake piston in this mode.
“Neutral Position Holding Mode.” This is a mode that allows the parking brake to be released for 15 minutes and is usually used for car washes, not pad slaps. Unless of course you’re the fastest slapper in the west!
“Temporary Cancel of Automatic Electric Parking Brake Mode.” Despite this mode saying “temporary” and the other one saying “holding” this mode releases the parking brake for much longer than the usual 15 minutes.
What does Honda have to say about servicing the rear brake pads?
Steps 1-3 are boilerplate nonsense: check the brake fluid, take off the tires, the standard steps. Step 4 is “enter maintenance mode.” This is huge. Supposedly, the scan tool is to retract the parking brake actuator piston, which it usually does. But when it’s time to exit maintenance mode you may run into a problem. It’s been my experience that the aftermarket scan tools can put the system into maintenance mode, but they seem to have a hard time taking it back out. Typically, you end up with limited throttle, all kinds of codes, and possibly limp-in transmission function. More often than not this ends up with a trip to the dealer on the back of a tow truck. My personal advice? Don’t let the system know you’re servicing brake pads.
In Step 4, Honda provides a note: you can manually remove the parking brake actuator and using a TORX socket, you can turn the actuator spindle clockwise until it stops. This will be a full retraction of the parking brake piston, but without using the actuator to do it. Before you do this, you’ll want to ensure the parking brake is not engaged—the manual says nothing about this. Put the system into “Temporary Cancellation Mode.” Put the vehicle in park with the ignition on, then turn the ignition off and within 2 seconds press the electric parking brake switch down. This should cancel the parking brake function until the next ignition cycle.
Here’s another look at the caliper with the actuator off. Note: both sides say to spin the spindle clockwise to disengage the piston.
Before you twist any spindles, get a clean sheet of paper and make some notes. How many turns does it take counterclockwise to fully engage the pads to the rotor? Just go until you feel some pressure and you can’t turn the rotor anymore. Count the turns and back it out to where it was originally. This is what I call “home position.” This is how far away the actuator prefers the piston is from engaging the pads. We’ll aim for this when we put new pads in. That way the actuator will be none the wiser.
Go ahead and back out the electronic parking brake piston fully, clockwise until it stops. Then service the rear brake pads as usual. Remove the caliper, press the hydraulic piston back in however you want—C-clamp, piston tool, by hand if you’re inclined. Clean up the slides and hardware, out with the old, in with the new pads, hang the caliper back on.
We have a caliper with 2 pistons retracted! The service manual doesn’t provide insight and we’re in a pickle. My solution? Think backwards. We have our caliper installed, and before that? You pushed that hydraulic piston back in. Know of a good way to push it back out? Jam on the brake pedal until it’s nice and firm. Don’t turn on the ignition. You’ll ruin your time without the parking brake operating—remember that “Temporary Cancellation Mode”?
Now we have our calipers hydraulically seated again. Recall when you turned the parking brake spindle clockwise? Go ahead and turn it counterclockwise. Do it until you get pressure and the rotor is locked up, then back it off the number of turns to that “home position” you recorded earlier. Maybe it’s a full turn, half turn, two turns—it’s going to be a bit different on every car. Put the parking brake actuators back onto the calipers.
Wrapping Up and A Free Cheat Sheet
So the pads are installed, the pistons (both hydraulic and electronic) are where they were before you touched anything, and the parking brake actuators are on. Go ahead and ignition on, turn the parking brake on and off a couple times, see that the parking brake indicator is functioning, and you have no codes.
Congratulations! You’re free and clear. I’ve created a cheat sheet about electronic parking brake service, so please download it and hang it up on your box. If you run into anything strange while working with one of these systems, or one fails and that’s why you’re touching it, give us a call at the Hotline and we will help you get it squared away. Happy wrenching!