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Old 08-29-2015, 01:44 PM   #1
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Brake Wear Light still illuminated

Just finished doing some brake work, at 80k miles. At all 4 corners, replaced the rotors (Zimmermans) and pads (EBC RedStuff). Also, on the fronts (where pads were less than backing plate thickness) I replaced the sensors (Sebro) since the warning light had started coming on. Didn't bother on the rears---there was LOTS of brake pad left.

Now the warning light is consistently on. I haven't pulled the wheels off yet to take another look, but I'm sure everything was put together correctly. Is there some common problem that I should look for? I can't even reset it with my scanner---not technically a CEL I guess, or a "safety issue" deemed too important to be reset by anyone other than one's dealership (or other shop equipped with the proper PIWIS tester.)

Funny thing is the consistency of the warning light. When I had next to no pad left on both fronts it was on for awhile, then off for awhile, then back on. Now it's ALWAYS ON..go figure.

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Old 08-29-2015, 02:49 PM   #2
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Quote:
Originally Posted by Frodo View Post
Just finished doing some brake work, at 80k miles. At all 4 corners, replaced the rotors (Zimmermans) and pads (EBC RedStuff). Also, on the fronts (where pads were less than backing plate thickness) I replaced the sensors (Sebro) since the warning light had started coming on. Didn't bother on the rears---there was LOTS of brake pad left.

Now the warning light is consistently on. I haven't pulled the wheels off yet to take another look, but I'm sure everything was put together correctly. Is there some common problem that I should look for? I can't even reset it with my scanner---not technically a CEL I guess, or a "safety issue" deemed too important to be reset by anyone other than one's dealership (or other shop equipped with the proper PIWIS tester.)

Funny thing is the consistency of the warning light. When I had next to no pad left on both fronts it was on for awhile, then off for awhile, then back on. Now it's ALWAYS ON..go figure.
If you replace the pad sensors that had triggered the light, there has to be something wrong with the sensors. Try jumping the circuit and see if the light goes out.
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Old 08-29-2015, 05:43 PM   #3
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Is the fit of the aftermarket sensors such that contact is disrupted as they are mounted/inserted? The same issue could be present at the connector.........been years since I had to deal with these so just a thought
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Old 08-29-2015, 07:05 PM   #4
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Also if you went with EBC red in prep for some track work, you should probably jumper at least your front sensors, on track it can get hot enough to melt them and cause the light to come on, when you are barreling down the hill on the back straight and hit the brakes at 120+ it will freak you out when that light comes on
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Old 08-29-2015, 09:46 PM   #5
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The brake wear light is the most simple circuit possible: If there is continuity, then the light is off. If the light is on, then continuity is broken somewhere in the wiring, connectors, or sensor itself. That's all there is to it. No computer, no software, no real sensors, no feedback loop - just a simple wire checked for continuity.

You'll have to re-check each sensor and connectors to find the cause. I usually swap sensors from wheel to wheel to find the bad sensor or in doing so, you'll eliminate the sensor that wasn't making a complete connection. Swap around, re-connect, and the odds are good that the problem disappears.
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Last edited by thstone; 08-29-2015 at 09:51 PM.
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Old 08-29-2015, 09:53 PM   #6
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The brake wear light is the most simple circuit possible: If there is continuity, then the light is off. If the light is on, then continuity is broken somewhere in the wiring, connectors, or sensor itself. That's all there is to it. You'll have to re-check each sensor and connectors to find the cause.
...or shorted to ground. The wire loop in the "sensor" only needs to be touching the rotor to trip the light (or any grounded metal surface), not necessarily broken. If the hole in the pad is not correctly spaced, the loop could be making ground contact through the pads metal plate.
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Old 08-29-2015, 09:53 PM   #7
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... you should probably jumper at least your front sensors...
No need for a jumper if you already have good sensors. Simply pull the sensors out of the pads and zip tie out of the way.
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Old 08-29-2015, 09:55 PM   #8
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...or shorted to ground. The wire loop in the "sensor" only needs to be touching the rotor to trip the light (or any grounded metal surface), not necessarily broken. If the hole in the pad is not correctly spaced, the loop could be making ground contact through the pads metal plate.
+1 Excellent point!
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Old 08-30-2015, 05:32 AM   #9
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All right, I'll play around with it first chance I get. May be a few days---working both days this weekend.

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No need for a jumper if you already have good sensors. Simply pull the sensors out of the pads and zip tie out of the way.
I understand the idea behind zip-tying them up and out of the way---I've considered doing that. But (forgive my ignorance): What's a "jumper"?

And to help me out in this process...If I were to simply disconnect ALL four of them, the circuits would be broken and the light would be on, Right? If that's true, then simply disconnecting one would do the same thing, Right? So if there's a bad one, what good will switching them around do me? I'd still have a bad one in the mix---the warning light doesn't care (nor indicate) where it's located. It's still gonna light up, Right?

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...or shorted to ground. The wire loop in the "sensor" only needs to be touching the rotor to trip the light (or any grounded metal surface), not necessarily broken. If the hole in the pad is not correctly spaced, the loop could be making ground contact through the pads metal plate.
I'll visually check them out for this. I get the concept, but I guess I don't fully understand why they're not automatically "shorted to ground" the instant they're plugged into the pads? Wait...a little light just came on here (mine!)...so the pad material is NON-conducting?

I might have a circuit tester layin around somewhere (I don't do electrical stuff much---pretty obvious I guess?), but that's all it would take to test the sensors, Right? If I don't, and assuming the holes in the pads seem to be placed properly, if I pull them one at a time and simply insert a small loop of wire, one end into each opening of where the sensor plugs in, I'll complete the circuit and the light'll go out, Right? (When I hit the bad one, that is.)

TIA. Sorry---I know I'm kind of a doofus when it comes to automotive electrical systems! The scary part? I once turned a 1-car garage into an additional bedroom (my excuse for buying all kinds of tools I wanted!), adding all kinds of wiring and switches and outlets and stuff. Lived there another 7 or 8 years and the place never burned to the ground!
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Old 08-30-2015, 06:47 AM   #10
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Correct - if you disconnect one the system will see the circuit as not complete and thus will illuminate. As thstone stated, it's a simple circuit... if complete then no light. If broken anywhere then you get light. A lot of people break/tear wire if not careful (squeezing the clip) in removing from old pads.

Assuming you still have one or both old front sensors, make a 'jumper' to test each corner (or rather two jumpers). Cut the wire ~ 2" from plug and strip back insulation to bare wire. Twist wires together securely and seal back up. Remove rear wheels and plug in jumpers in lieu of original sensors. If light goes out then you know at least one rear is issue. Chase down by plugging the pad sensor back in one side at a time. Same for front if issue not vetted on rears. Since front are new they are less likely to be bad... assuming reputable parts sourced.

Personally, pads in 9x6 and 9x7 series are easy enough to visually check (and I always inspect wheels off on mine before and after each DE). As such, all four corners on my track car are jumper aka shorted sensors. Same as above except I solder the wires then fold and double heat shrink wrapped remaining 3/4" stub. Pretty sure I have a picture around someplace and will look to find.

Good luck
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Old 08-31-2015, 11:53 AM   #11
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Ran into the same issue recently except I didn't replace the sensors because some idiot forgot to order them. (yeah. That was me.) So when I finished, of course the light came on. I finally got the sensors and decided to gamble on which one it was. Guessed right on the money with the first wheel. The wire got pinched up and was broken. Replaced the sensor but still the light was on. So I replaced the other three and still have the light on.

I bought a meter and will be checking the sensors for continuity and then I guess checking the plug for voltage (I'll guess 12).

I'm not sure I understand what particlewave is saying about the wire grounding elsewhere. If the wire is not broken, I don't get how it could ground to something.
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Old 08-31-2015, 12:05 PM   #12
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If there is missing insulation on any wire and it's touching metal, it could be shorted to ground. The "sensor" is just a bare loop of wire. If it is touching any metal, it is shorted to ground and will trip the brake wear light.

The circuit is one big loop that starts and ends at the instrument cluster. Positive voltage is fed to one wire and returns on the other. Any break or short in that loop will trip the light. The base plate for the pads is metal, so if the sensor hole in the pad is not placed correctly, the bare wire of the loop in the sensor could possibly make ground contact there. I only mention it because one of my 8 new pads did have a misplaced hole that could have allowed a sensor wire to touch the base plate.

My point was that you should keep an eye out for any cracked or missing insulation where a bare wire could touch metal.

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Old 08-31-2015, 12:39 PM   #13
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Gotcha. Thanks.
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Old 08-31-2015, 12:55 PM   #14
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Visual aid. Each "U" shape is a pad sensor. Black circles are rotors. Anything that stops the voltage from returning to the cluster will trigger the brake wear light.




Example: absence of voltage at the right rear sensor does not mean that is where the problem lies. The problem sensor/wiring could be anywhere in the loop before that (front left or front right).

Last edited by particlewave; 08-31-2015 at 12:57 PM.
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Old 07-07-2016, 11:30 AM   #15
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I must have a high tolerance for warning lights. Didn't realize it's been almost a year and I haven't started diagnosis yet.

I went and pulled all four tires today. I unplugged the sensor and checked continuity between the two holes. Lucky me! All four showed good. Unlucky me! My brake wear light is still on.

Before I start tearing everything apart, is there a KISS (Keep It Simple Stupid) thing I should be looking at? This problem started when I replaced my rotors and pads. A week later, I replaced all the sensor wires to no avail.
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Old 07-07-2016, 10:04 PM   #16
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Old 07-08-2016, 04:57 AM   #17
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Check and make sure all the plugs are fully seated in the sockets. I failed to push one fully in and I lived with this problem all last winter.
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Old 07-08-2016, 06:37 AM   #18
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I wish I had a bigger garage. I'm gonna try to get all four tires off today and jump all of them at the same time to determine whether it's the sensors or whatever comes after the sensors. I'm thinking I might have continuity, but maybe a sensor is partially grounding somewhere so while I'll have continuity, I might not be getting all the voltage through when the car is on. I'll keep all posted to my findings.
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Old 03-12-2017, 10:02 AM   #19
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Is there polarity on the sensors which must be followed when you reinstall new ones?

I just replaced the front pads and rotors and all hardware including new sensors and my brake wear light is on. It was NOT on prior to the work. When I inserted the sensor into the pad, I didin't really hear a "click" to lock it in. does that matter? It is still seated in the hole. Perhaps I have bad sensors ( I highly doubt it). Probably user error on my part.
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Old 03-12-2017, 10:18 AM   #20
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No polarity that I can remember. You just need to check your connections.

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