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Why is My Brake Light On Diagnosing Common Brake Failures

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Created on: 2019-10-19

Your brake light just came on, now what? Here are a few things you can check yourself, before paying expensive diagnosis fees at a shop!

  1. step 1 :When the Brake Light Comes On
    • Pull over safely
    • Check the parking brake lever or foot pedal to ensure it is not accidentally engaged
    • Pump the brake pedal to make sure the brakes are not soft or spongey
    • Check the brake fluid level
    • It's best to tow the vehicle if the issue can not be resolved at the roadside.
  2. step 2 :Diagnosis at Home, or In the Shop
    • Scan the vehicle with an ABS capable scan tool
    • Visually inspect brake pad wear sensors, if equipped
    • You may circuit test brake pad wear sensors if they triggered a code
  3. step 3 :Further Steps
    • If the fluid was low inspect brake calipers, hoses, and lines for leaks
    • Check the brake master cylinder for leaks
    • If the fluid was low but there are no leaks, check the brake pad thickness

Tools needed

  • Scan Tool

    Jack Stands


    Floor Jack

You ever driving around and up pops on your dash a brake warning light indicator? What do you do?

As soon as that light comes on, you want to make sure you pull over to a safe location. All right, when you're pulled over safely, the first thing I would do is check the parking brake. Just make sure it's not clicked up one tier because if it's clicked up one tier, that's all it takes to have the light come on. So, just make sure that that's all the way down. If you have a foot pedal one, then check the foot pedal one.

And then check the brake pedal. Give the brake pedal a couple pumps. See if it feels spongy or if it feels normal. With the car off, it should feel a little bit stiffer than normal. So, check that.

Then pop the hood. In this vehicle, our brake fluid is located right here. You want to check the brake fluid level. Just make sure it's up to the actual line. If it wasn't your parking brake, and the light's still on and you don't know what's going on with it, it's a good idea to have the vehicle towed.

Now that I'm back at the shop, the first thing I want to do is scan test the vehicle with a scanner that actually works with ABS modules. This scan tool is hooked up to the vehicle, and I have the key on. There is a bunch of history codes in the ABS module, but the bottom one that is current that is causing our light to come on happens to be the brake wear indicator for the rear brake pads, so that's what we're going to go check out next.

The rear brake pad wear sensor is located right here, right next to the pad. It's actually attached to the pad. Now, what you want to check is the gap in between the pad sensor and the rotor and make sure it's not touching. Checking the brake pads, you can see if the sensor is actually touching the rotor. In our case, it's not touching the rotor. Because that's not the case in our situation, we're going to have to check the sensor out itself.

I'm going to look at the wire, just to make sure the wire's not rubbing on anything. Check the routing of the wire. It looks pretty good. I don't see anything shorting out. I'll follow this wire all the way back here, and it's past the blue connector. Happens to be the black connector in this vehicle. Just pull that out, and disconnect the connector. Push down on the button and separate it, just like that. Look inside there, see if you see any corrosion, anything green. It doesn't look too bad. Check the rest of the wiring harness, see if anything looks broken. Looks pretty good.

I'm just going to pull the sensor out and just test it. Disconnect it here. I'll just use some needle nose pliers, pull out the sensor. Now, when I was taking it out, these wires are very, very thin, as you can see. They are pretty brittle, so they broke on me. The connector end broke, and the sensor side broke, and the wire. That's basically what makes up the sensor. This sensor side goes into the pad, right here, just like that. And then, when the pad gets thin, the rotor will cut this side of the sensor, open the circuit, and that will cause the light to come on.

If you wanted to test this sensor to see if it was actually bad or not, what you can do is take a multimeter. We want to check for continuity, so we go to the circuit test. Right now the meter says one. Check the meter. Just check the terminals together and you get a beep. That'll be good. And then what you want to do is touch the two terminals on the inside.

Now, obviously, this is kind of difficult to get in there, so you might need to put some extensions in there. This sensor obviously is going to test open, but you should get something like that if the sensor is good. Some sensors have resistance, so you would have to put this meter on resistance, put it on 20k ohms, and then you should get some reading, which obviously this one's not going to ... We can't test this properly, but that's how you would test it.

Now, if you didn't have a scan tool to check the ABS module, what you could do is go to each individual brake pad sensor and check it with a meter. Make sure they're not an open circuit.

If your brake fluid level was low, what do you want to do is check and find where there's a leak. See if there's any brake fluid at the calipers or any of the brake hoses or the brake lines themselves. Follow the lines throughout the car. Normally, you'll see a puddle on the ground. Sometimes the brake master cylinder will actually leak brake fluid into the brake booster, so don't forget about that.

If you can't find any leaks anywhere and your brake fluid level is low, you might want to check your brake pads. If all the brake pads are thin, it's going to cause the level to go down pretty far and could cause your light to come on. Now it's time to do some brakes.

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