Dash brake light on.... Any ideas where to look? - JeepForum.com
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post #1 of 11 Old 10-18-2019, 03:07 PM Thread Starter
Ravenbar
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Dash brake light on.... Any ideas where to look?

Parking brake lever is all the way down and brake fluid is topped off. Brakes seem to work fine.


Odd part is it started after I changed the bulbs in the gauge cluster and I've had an ABS light on for a while(bad sensor, was on the to do list for this weekend), but that's gone now. Almost wondering if it's a wiring problem in the dash rather than an actual brake issue.


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post #2 of 11 Old 10-25-2019, 06:13 PM Thread Starter
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OK, spent some time this week trying to figure this out, but I'm more confused than before.



Brakes seem to ork fine. Had ABS light on for quite a while for a bad sensor. Also had a bad ABS module, but replaced that over the summer with a used one off an '04 Freedom edition with 94k miles(same vehicle as my transmissions out of and I also have the engine as a spare). Mines an '02 laredo with over 230k miles. ABS light isn't lighting up at all now, even during the initial key on light check. I've pulled the dash and replaced the bulb with no change. I've also checked both the under hood and under dash ABS fuses which visually look to be good. The Brake light is also intermittent. If I travel say from work, to the bank, to the store, then to home(as I did last night), the Brake light was on for the first 2 trips, but off for the rest. Had trips where it was on no matter what and also trips it was on all the time. It also has a delayed coming on, When I start the Jeep, it doesn't come on initially, but then shorty later it will,doesn't matter if I've pressed the brake pedal or not. Seems as it running a test, failing, then the light comes on.



I'm thinking ABS module failure... Haven't been able to get my scanner(Bluedriver) to connect to more than basic codes lately(has worked in the past which is how I know a sensor was bad and also an airbag sensor), so can't tell if it's actually throwing any codes.

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post #3 of 11 Old 10-25-2019, 06:44 PM
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This one is out of my wheelhouse so to speak but maybe there's a problem with a tone ring sensor or associated wiring. The same goes for the circuit to the parking brake lever sensor.

I too suffer from the debilitating effects of a seemingly random, intermittent dash brake light but so far I've not seriously contributed the resources of time and effort that may be necessary to find a resolution.

I'm not entirely convinced I need a brake light anyway and so I may end up just replacing the bulb with a suitable resistor (if you just pull the bulb I believe that triggers the "check gauges" light).

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post #4 of 11 Old 10-26-2019, 07:10 PM Thread Starter
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Originally Posted by 99wjtx View Post
This one is out of my wheelhouse so to speak but maybe there's a problem with a tone ring sensor or associated wiring. The same goes for the circuit to the parking brake lever sensor.

I too suffer from the debilitating effects of a seemingly random, intermittent dash brake light but so far I've not seriously contributed the resources of time and effort that may be necessary to find a resolution.

I'm not entirely convinced I need a brake light anyway and so I may end up just replacing the bulb with a suitable resistor (if you just pull the bulb I believe that triggers the "check gauges" light).

Interesting to know the ABS/tone ring sensors, are connected to the park brake switch. I've had a bad sensor for quite a while, just haven't got around to getting a sensor.

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post #5 of 11 Old 10-26-2019, 07:28 PM
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In reviewing wiring diagrams, the wheel speed sensors, the "brake warning indicator switch" and the "brake lamp switch" all connect back to the ABS controller which apparently uses an internal "red brake warning indicator driver" to illuminate the brake light for faults.

I don't know what criteria the controller uses when deciding whether to illuminate the brake light, the ABS light or both, but at any rate, yeah, the ABS/tone ring sensors and the parking brake switch are connected, albeit indirectly, through the ABS controller.
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post #6 of 11 Old 10-26-2019, 09:56 PM
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The red brake light should only come on when the parking brake is engaged or if a loss of hydraulic pressure is detected in the brake system.

The ABS light only comes on for issues specifically related to the ABS.
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post #7 of 11 Old 10-27-2019, 06:39 AM
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So there you have it. If the service brakes are normal, then the problem should be in the parking brake lever position detector switch (most likely), its circuit or the ABS controller itself, which is what that circuit appears to connect back to.
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post #8 of 11 Old 10-27-2019, 07:48 AM
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Red brake light is 1) parking brake 2) master cylinder switch
Both switches are NO. Suspecting a bad switch next thought is a wire grounded.

lets try unplugging one at a time and see if we can pin this down.
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post #9 of 11 Old 10-27-2019, 03:15 PM Thread Starter
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Quote:
Originally Posted by 99wjtx View Post
In reviewing wiring diagrams, the wheel speed sensors, the "brake warning indicator switch" and the "brake lamp switch" all connect back to the ABS controller which apparently uses an internal "red brake warning indicator driver" to illuminate the brake light for faults.

I don't know what criteria the controller uses when deciding whether to illuminate the brake light, the ABS light or both, but at any rate, yeah, the ABS/tone ring sensors and the parking brake switch are connected, albeit indirectly, through the ABS controller.

That's the real question right there, which probably no one outside a dealer would have the answer to, what criteria results in the brake light coming on.



Update: OK,just did a bit of digging in the FSM and I found the following"

"The brake indicator gives an indication to the vehi-
cle operator when the parking brake is applied, when
there are certain brake hydraulic system malfunc-
tions as indicated by a low brake hydraulic fluid level
condition, or when certain faults are detected in the
Anti-lock Brake System (ABS). "


So ABS could trigger that light. Still reading as to what the cause could be.




Quote:
Originally Posted by AVR2 View Post
The red brake light should only come on when the parking brake is engaged or if a loss of hydraulic pressure is detected in the brake system.

The ABS light only comes on for issues specifically related to the ABS.
Quote:
Originally Posted by jtec View Post
Red brake light is 1) parking brake 2) master cylinder switch
Both switches are NO. Suspecting a bad switch next thought is a wire grounded.

lets try unplugging one at a time and see if we can pin this down.

Already unplugged the master cylinder switch and I immediately get the brake light on. Normally, when it comes on, which isn't all the time, there is a delay, such as its running a test, then failing it.

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post #10 of 11 Old 10-27-2019, 05:01 PM
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Quote:
Originally Posted by Ravenbar View Post
That's the real question right there, which probably no one outside a dealer would have the answer to, what criteria results in the brake light coming on.



Update: OK,just did a bit of digging in the FSM and I found the following"

"The brake indicator gives an indication to the vehi-
cle operator when the parking brake is applied, when
there are certain brake hydraulic system malfunc-
tions as indicated by a low brake hydraulic fluid level
condition, or when certain faults are detected in the
Anti-lock Brake System (ABS). "


So ABS could trigger that light. Still reading as to what the cause could be.
Yes, that's more like what I recall from past threads on the topic which hashed it out and concluded that a tone ring sensor or fault in one those 4 circuits could trigger the brake light.

At any rate, I believe there are professional Chrysler/Jeep techs who post here (who are appreciated) and so obviously I don't feel the need to second guess those guys, but everyone is capable of making mistakes or being unsure about something.
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post #11 of 11 Old 10-27-2019, 08:41 PM Thread Starter
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Originally Posted by 99wjtx View Post
Yes, that's more like what I recall from past threads on the topic which hashed it out and concluded that a tone ring sensor or fault in one those 4 circuits could trigger the brake light.

At any rate, I believe there are professional Chrysler/Jeep techs who post here (who are appreciated) and so obviously I don't feel the need to second guess those guys, but everyone is capable of making mistakes or being unsure about something.

Did a little more reading and found this:
" Communication Error - If the cluster receives
no lamp-on or lamp-off messages from the CAB for
six consecutive seconds, the brake indicator is illumi-
nated. The indicator remains illuminated until the
cluster receives a single valid lamp-off message from
the CAB."


Had to go do laundry tonight and it took exactly 6 seconds for the brake light to come on. Stole the instrument cluster from my parts rig and swapped it. Figured since this started after I pulled the instrument cluster that was a good place to start. No more Brake light on, and the ABS light is sometimes coming on, just as before this started. Not calling it fixed yet since the issue was intermittent before.

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