ABS/Brake warning light flashed and dings constantly


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2002 envoy. the ABS/Brake warning light flashed and dings constantly. pull codes and there is nothing there. any advise on what the problem might be?

thank you
Make sure your parking brake isn't up by a single click. If it is, the brake light will go bonkers along with dinging.

You won't get any ABS codes via a normal scanner as those usually only do powertrain (P) codes. You need one that can read body and ABS codes.


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If it comes down to cases and other things don't work... THIS repair is a bit work intensive but is often a... Killer Fix for unexplained, intermittent ABS Sensor Dashboard Light events... especially on 10 Year Old TBs & Envoys in the Rust Belt or in Winter Time Salted Road Regions:

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this morning I checked all the brakes shoes, took off the ground wire and clean, ruffed up and reseat, checked e-brake and still get the lights and dings. moving on to other things keep you posted
Coincidentally, I've just run in to this very same problem. Think MRRSM has got you pointed in the right direction with a wheel speed sensor. Here are my symptoms. Might help you diagnose. I don't have this completely solved yet. Not trying to hijack this thread, but I'm battling the same exact thing.

Left front brake has been "grinding" when engaged on rare occasions for several years. Changed pads, rotors, and fluid about a month ago. Still getting the occasional grinding. I came to the conclusion that its the ABS engaging on that wheel.

Wife started complaining about a week ago that the ABS light was coming on occasionally (the TB is her DD). It would not stay on - just on and off randomly (seemingly). Decided it was time to clean the left front speed sensor per the video above.

Took everything apart yesterday morning. I have Timken hubs on my truck. They put a small stainless steel tab under the speed sensor mount, presumably to combat the lifting issue from corrosion. When I pulled the speed sensor, I could see purple grease in the cavity where the toothed sprocket is located. Many of the teeth were bridged with grease. I had a spare Timken hub (not new, but not failed either). Decided to take the speed sensor off the spare and install it.

Well, changing the speed sensor made things a lot worse. ABS light was on constantly AND random brake light with chimes - almost non-stop- just as the OP describes. You can get the exact behavior described by the OP due to a speed sensor.

At that point, I decided to change the hub. Figured it was close to failure anyway with the purple grease in the sprocket cavity. It was about five years old with about 80,000 mi. Didn't want to put the used Timken on. Had to buy a Moog from Autozone. Killed me to pay $180 when I could have got a Timken from Amazon for $125, but I wanted to get this done.

After installing the new hub, ABS light is still going on and off, but the brake light and chimes have stopped. ABS light will shut off for a couple of miles and then come back on for a few miles. Essentially, I'm back to square one. Starting to think I'm barking up the wrong tree with the left front speed sensor. I have the Torque app which, as was already mentioned here, won't read ABS codes. Was seriously starting to think about taking it to the stealership to read the ABS code rather than keep guessing. Decided not to give up so easy. This truck has not seen the inside of a stealership or any other repair facility in over 11 years due to help from this site and OS before that. Decided to buy the BlueDriver bluetooth transmitter for $100 to use with their app. Claims to read ABS codes. Figured it would cost me about that much to have the stealership read the codes anyway.

BlueDriver thing will be here tomorrow. I'll let everyone know what it says.
BlueDriver arrived today. It does read all codes as advertised. There were 12 stored ABS codes. The BlueDriver app gives you suggested fixes for each code. Nearly all of them suggested replacing the ABS controller. Guess that's my next move. I'll start another thread asking for recommendations on ABS controllers.
Before going and replacing anything, post up the codes here. Could be something as simple as a bad ground or power issue.
I did remove and clean the ground that's right around the corner from the ABS controller yesterday. Didn't change the behavior. ABS light is still going on and off.

Here are the codes:

C0265 - Valve relay coil circuit open
C0245 - Wheel speed sensor frequency error
C0241 - PCM Indicated requested torque malfunction
C0251 - RTD indicated fault
C0252 - ABC sensors uncorrelated
C0246 - Simultaneous dropout of both front wheel sensors
C0242 - PCM indicated TCS malfunction
C0237 - TCS throttle position signal malfunction
C0223 - LF ABS channel motor free spins
C0222 - Rear ABS channel in release too long
C0221 - RF ABS channel in release too long
C0226 - LF TCS channel will not move

Some of these codes may have been stored when I changed the speed sensor on the left front and had all the chimes, brake light, and ABS light. I cleared everything with the BlueDriver. I'll check what pops up tomorrow.
Almost sounds like a connector issue, like somebody pulled a plug. Maybe some were historical and clearing them may leave actual current issues.
Where did you get the Blue Driver?
Ordered it off Amazon. Came with free one day delivery. I haven't spent much time playing with it, but at first glance, it doesn't seem to have as wide of range capabilities as Torque (other than the ability to read codes from all the vehicle modules).

it seems somewhat "catastrophic" with such a large list. Of course, you have checked all the fuses including confirming voltages therein.
Haven't checked any fuses or voltages. I'll try that.

Wife says the ABS light is still going on and off randomly as she drives. I hooked up the blue driver last night. It's reporting no stored codes. The ABS light was not on at the time. I'll try to drive it until the light comes on with the blue driver hooked up to see if I can catch the code.
Yes, because sometimes, it will not store the codes when the ignition is turned off.

Also try another thing, pull all the ABS fuses for 30 seconds. I had a weird ABS light issue with no codes on another vehicle and resetting the module worked for me.

Off topic: The Blue Driver is overpriced and geared more towards really novice users. A generic bluetooth adapter can get all modules' codes using the Car Gauge Pro app. Although it is capable of capturing live data, Torque has a much more refined interface. I use Car Gauge Pro for non-powertrain codes and Torque for everything else.


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I finally have time today so I will be digging into this today. good stuff above, thx.

I have also read that it could be the ignition switch, any thoughts on that?


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As mentioned a few times here, did you use a scanner capable of pulling ABS codes?
Shit can get real expensive if you're replacing parts with blinders on!


Active Member
scanner with ABS should arrive today. pulled sensors and cleaned area and sensors. was off for about 5 minutes then returned full on, still get the lights and ding. so when the scanner arrives we will see what it says.


Active Member
I have totally misrepresented this problem, sorry. I don't have a ABS issue. it is just the BRAKE lights n chime issue. ( ! ) ( P ) lights on and chime. I have checked all the pads (perfect) fluid level and ground. next is the emergency brake switch and then the fluid level sensor.
Ah, and we also have a second poster with an ABS issue so this thread is getting mixed up. I may split these up into separate threads.
My fault for hijacking this thread, but I had the exact same behavior reported by the OP.

Mooseman, you were wise to tell me not to start throwing expensive parts at my problem.

Blue driver is consistently recording C0221, C0222, C0223. According to the service manual (provided by Mooseman), these are all associated with the right front wheel speed sensor. That's a nearly new Timken hub. I replaced it about six months ago. I will go back at Amazon and see if they will send me a new one under warranty. I'm confident that will fix the problem.


Active Member
removed, inspected and reinstalled e-brake switch (simple spring switch), replaced brake fluid level sensor (cheap) and still have the problem. whats next? does anyone know how to check voltages and where? is the ignition switch a possible culprit?
The ignition switch is a known source of electrical gremlins however never heard of it causing ONLY the brake warning light.

You would need to check the manual for schematics to see where/what circuits would turn on the light.

Years ago on an older truck (maybe my '93 S10 Blazer), I had an ABS issue and wanted to kill the ABS light so I pulled the bulb. Well, that caused the brake light to come on. Maybe check that the ABS system is OK.


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removed, inspected and reinstalled e-brake switch (simple spring switch), replaced brake fluid level sensor (cheap) and still have the problem. whats next? does anyone know how to check voltages and where? is the ignition switch a possible culprit?
take the switches / sensor connectors off and use a meter to check their continuity accordingly... when the switch is not being activate by the brake leveler and and when it is... see if you meter a difference. Same with the fluid sensor... check the old one first for "practice".


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I think I now know what the problem is, a bunch of gunk in the bottom of the master cylinder which prevents the optical sensor from being able to read the fluid level on a constant basis. decided to replace the brake fluid but while using a turkey baster to remove the old fluid it really stirred things up which showed a bunch of garbage in the cylinder, stuff turned dirty crap quickly. I decided to just go ahead and replace the master cylinder (since to really clean it I would have to remove it) and purge the system and replace all fluid. waiting for cylinder to arrive. keep you posted.
Can you replicate the issue by unplugging the sensor at the master? If so, it gives you a starting point.


Active Member
spoke with a GMC mechanic and after much discussion he is pretty sure it is a short in the BCM. so looking for a used BCM that will match what i have.

anyone know a quick way to turn off the chime?
You could unplug the driver side door speaker as all those sounds come through there.


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eBay has a decent list of Body Control Modules and Sub-Components available... but be advised that the ENTIRE BMC is what you are after and NOT just a sub-set or sub-assembly portions of this unit. If you find one that is Complete and under $100.00 ... Don't wait too long to get it ...as these are becoming as scarce as Hen's Teeth. You will need access to a TECH 2 Scanner in order to program the Used or New Replacement onto the Databus of your Envoy:

THIS is a more precise listing of what you want to go after:



...and other possible items to consider:



Please let me know what you intend to do about getting this aforementioned listing... as otherwise... I will obtain it for my 2002 Trailblazer if you decide NOT to make this purchase. Under your present circumstances... It seems only fair that you deserve a Head Start.
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You will need to have it reprogrammed to your VIN as well as a security relearn with the PCM. You might also have to get everything synched back with all the other modules as well since the BCM is brain that runs everything. Not a trivial swap.


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surely, you want to do the simple checks first. Just unplug the sensor connector at the brake system / tank and see what changes. Further, although I haven't check yet, but if nothing changes, make it change by causing a "short" on the connector (maybe need a resistor) and see what changes. It would be "foolish" to change out the BCM IF the problem is a "short" somewhere else (ie. wiring) which changing out the module isn't going to help other than "emptying" your wallet.


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... as long as you bear in mind that a "...Faulty EBCM..." IS on the list of the possible causes and origins of these problems:

Here is an Excerpt from this On Topic URL coverage:

C0222 Missing Right Front Speed Signal

C0223 Erratic Right Front Speed Sensor

Probable Cause

1. Open or short circuit condition
2. Poor electrical connection
3. Faulty wheel speed sensor
4. Faulty EBCM

The thing to do, is follow the wiring back to the EBCM. Disconnect it there, and connect an ohmmeter to the sensor side of the wiring. If you get a reading other than infinite resistance, wiggle the wiring with the ohmmeter still hooked up, and see if it goes open. If you get an open reading right away, go to the shorter sensor lead, and check again there. If that reads continuity, there is a break in the secondary lead. If you get continuity at all times, switch to an AC volt meter at the sensor side of the lead at the EBCM. While spinning the wheel fairly quickly by hand, you should get a reading of about 1/2 volt.

If you do, there may be a problem with the EBCM, or with the connection there. If you do not read AC voltage while spinning the wheel. you may have a 2nd faulty wheel speed sensor, or a sensor that's not properly seated, or some sort of debris between it and the Tone Exciter Ring. The gap between the sensor and ring has to be very precise. Any rust buildup or such on the mounting can hold the sensor too far away, preventing a sufficient voltage from being generated. Likewise, rust debris in the teeth of the ring or sticking to the sensor can prevent a voltage from being generated. or make it very weak.

Source(s): ASE Certified Tech
I've worked on earlier systems, where you actually had to set a very precise air gap, and also seen ones with rust sticking to the magnet preventing them from working properly, which is much more common with the older open types.


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