How long do brake pads last, really? If you’re wondering when to change brake pads on your ride, your vehicle will let you know. And it won’t give you some vague answer like: “Every 30,000 to 70,000 miles, depending on your driving style.” Nope. Whether you drive a Silverado or a 7 Series, it’ll tell you EXACTLY when to change brake pads — your brake pads. Because it’s a warning, courtesy of your brake sensors, which act kind of like Mack in the old Dr. Seuss story. (More on that in a moment.) Here’s a link to the Carlson sales support page, if you need to order new electric wear sensors. — Motor City Mitch
On my seventh birthday, my folks gave me a Hot Wheels car called the Splittin’ Image and my Aunt Sarah gave me a book. Naturally, I spent more time racing the car (I liked the twin-cockpit design, though it always lost to my Camaro). But I remember the book: “Yertle the Turtle and Other Stories” by Dr. Seuss. The main story was about a king turtle (Yertle) who ordered his fellow turtles to climb onto one another and form a tower. Then he sat on top. As the tower grew, his view got better. But there was a problem. A turtle at the bottom, named Mack, kept complaining about the weight. Yertle ignored Mack until he burped. And the reverb from his burp knocked the king off his perch. It was a good story.
I mention it because brake sensors remind me of Mack. In the array of 30,000 parts that make up your whip, they sit almost at the bottom — right next to your brake discs. They endure a lot of abuse, from the heat of braking to the toils of the road. And their sole job is to warn you (and in doing so, they get ground into the rotors and destroyed).
Most people probably don’t know they exist. But if you drive far enough your brakes will wear down. And when that happens, a brake sensor will warn you about it. It might warn you with a squeal or a warning light on your dash. But however the message arrives, it’s time for you to get a brake job.
TYPE 1: SQUEALERS
Brake wear sensors come in two main types: mechanical and electrical. Most vehicles have the former, so we’ll start there.
Sometimes called metal indicators, metal tabs, scratchers, or squealers, these sensors are simple and effective. One end attaches to the back of a brake pad (although there are some clip-on types). The other end extends a few millimeters up along the edge of your “friction material” — the “meat” — on your brake pad. (This is the stuff you press against your rotors when you brake.)
The pads wear down over time. And when they wear down far enough, your metal tab touches the rotor and the squealing begins.
To show you what that squealing sounds like, the YouTube channel called Blu-TSX mounted a camera near the right rear wheel of a 2010 Acura, where the brake pad had worn down enough to engage the metal tab. The tab makes a good deal of noise when being driven either forward or backward (although no noise when the driver hits the brakes). Here’s the sound…
And for the sake of variety, another YouTube mechanic, Eddie Carrara, posted a video to show what a metal brake tab sounds like on three different cars, all of which he drives both forward and backward — demonstrating the sounds.
He also shows how the sound goes away when he brakes. By stepping on the brake, he’s pushing the metal tab firmly into the rotor, changing the vibration so you don’t hear noise. Here’s his video…
OTHER SQUEAL CAUSES
One downside to mechanical tab sensors is that there are other reasons your brakes could be making noise. The next video is by Eric Obrochta on the Allstate channel. (I normally see Eric on his South Main Auto Repair channel.) He goes through three possibilities:
- First, metal-to-metal contact — e.g. where the pistons meet the pads.
- Second, worn brake hardware — the clips that hold your brake pads. (A 2016 lab test found that worn clips squeak more than new ones.)
- Third, dirty slots in the caliper bracket where the pads slide back and forth. (Eric says his shop normally uses a sandblaster to clean these.)
Here’s his video…
In theory, you could have a brake sensor next to every pad you’ve got, but it’s not necessary when you think about it. Inside pads tend to wear out first, so why have sensors on the outside pads? And the right and left brakes, whether in front or in back, will normally wear out at about the same time. So having one sensor on one side, front and back, gets the job done.
For metal tab-style sensors that are attached to a brake pad, you replace the sensor automatically when you replace the pads. You order new front pads — two for the left and two for the right — and typically one will have the sensor.
That’s the case in the following video by Dial2Fast, where the mechanic finds a squealing tab on the rear passenger side of a Nissan Quest. He does a great job of showing what a worn tab sounds like, where it is, how it’s wearing down, and what to do…
TYPE 2: ELECTRIC WEAR SENSORS
While mechanical sensors are more widespread right now, their main alternative — electric wear sensors — are on the rise.
“They’re becoming more common,” says Chris Miller of International Brake Industries. “They’re on a lot of European cars, but not all. They’re on more expensive vehicles, with a trickling down to less expensive ones — for example, the 2019 Chevy Silverado, front and rear.”
A look at Carlson’s latest wear sensor flyer on the the sensor product page will show you a complete list of vehicles covered. If you drive a newer-model European car — Audi, BMW, Mercedes-Benz, Mini Cooper, Porsche — you probably have them. The same holds true for a late-model Cadillac, Camaro or Corvette.
In some ways, electric sensors are identical to their metal counterparts. Both types normally go on an inside pad — often with one sensor in front and one in the rear. Also, both types extend up a few millimeters from the the bottom of your pad, along the friction material or “meat.” In the process of touching the rotor and warning you, both types get destroyed.
And finally, both need to be replaced when you get new pads.
The difference? Electric sensors don’t warn you with a squeal. That’s an advantage because brake noises, as noted above, can be caused by various brake problems. An electric sensor tells you with near certainty that at least some pads are worn out, and sometimes (via a scan tool) which pads they are.
Electric sensors do this by sending an electric signal when they contact the rotor.
TWO TYPES: MAKE OR BREAK
If the electric brake sensor is a looped wire that sends an electric signal when it contacts your rotor, there are two ways it can work. One way is to send a signal if your rotor simply touches it — that contact causes a change in resistance that triggers a warning. The second way is to send a signal when your rotor severs the wire, breaking the circuit. Again, this causes a change in resistance a triggers a warning. The first way “makes” a circuit and the second way “breaks” it.
In the following video, Peter Finn the Car Doctor really shows how this works. He loops a wire and connects it to a multimeter, showing the reading before and after he cuts the wire. Then he does the same thing with a brake sensor, attaching it to the multimeter. You can see the same electrical change — the change which triggers the warning…
REPLACING SENSORS ON A BMW 3 SERIES
Electric wear sensors vary between makes and models, but they have one thing in common: One way or another, one end inserts into a brake pad while the other end connects to the vehicle’s electrical system.
In this next video, by Auto Repair Guys, the mechanics replace the sensor on the front of a BMW 325xi.
The mechanic has a thick accent but the camera work and lighting make it easy to follow. He starts in the driver’s seat, showing the warning light and the reading on his scanner — an Autel MaxiCOM scan tool — which tells him both the front and rear pads need replacement.
He opens his package of two sensors — one front and one rear — and then shows how to remove the old sensor from the front and replace it with a new one. He explains how the sensor wire was incorrectly connected to the chassis with cable ties during a previous brake job, and how to do this right. And he shows where the sensor plugs into a box in the chassis, a box that also holds the ABS sensor connection.
REPLACING SENSORS ON A MERCEDES ML 350
This next video, on a channel called iRepair Autos, shows how to change an electric sensor on a Mercedes ML 350. The mechanic starts off by showing the warning light — BRAKE WEAR – VISIT WORKSHOP — on his dashboard.
Outside the car, he explains how he’s already checked the front wheels, and that worn sensor is on the rear passenger side. Before he takes off caliper bracket, he shows how worn the pad is. (This sensor, by the way, doesn’t route to someplace deep in his car but instead to a connection port in the caliper.) Then he puts on new pads, plugs in a new sensor, and puts the caliper bracket back on. Done!
REPLACING SENSORS ON A LEXUS
This next video, posted by BriansMobile1, shows an electric wear sensor for a Lexus LS400. In the video’s description he adds that this applies to Lexus and Toyota sensors.
Brian does ONE thing in the video: he shows how the sensor attaches and detaches from the brake pad.
There’s a little clip — a third part in addition to the pad and sensor — that he pries off. Then he pushes the sensor out of a little metal collar holding it in place.
We’re almost done. There’s ground we didn’t cover, but I hope I’ve put a spotlight on some humble parts that do what they need to do and do it well. That’s the point of any part, right? In this case , it’s a lookout in your brake system warning you EXACTLY when to change brake pads. It’s a “Mack,” giving you a simple, no-nonsense answer to the question: “How long do brake pads last on MY car?”
Finally, wear sensors aren’t alone. They have cousins in and around the brake caliper: fellow parts getting exposed to the heat and the toil of the road. These are parts that wear out along with your pads. Think about replacing them when you get a brake job. Most likely it’ll mean quieter and better brake performance, and more time between brake jobs. Here are a few of those parts: