Brake light on! Need tech help now!!! [Archive] - GrandAmGT.com Forum

PDA

View Full Version : Brake light on! Need tech help now!!!


3800SII
06-20-2011, 09:14 AM
Ok, it has been a while since I have posted on here. Just to let everyone know my turbo system is still running strong. I love my GrandAm, but I hate the silly electrical issues that keep popping up.

My brake light has been on for the past 4 months now, and I am up to my wits end with trying to figure out EXACTLY WTF is the problem. I have searched both GAGT and GAOwners forums and tried almost everything there is with the exception of changing out all the brake hoses and body control module. Here is a list of everything that I changed so far:

1. I replaced the Master cylinder and bled the brake lines. Fluid is filled to the top
2. I replaced the passenger side caliper which was seizing. Works good as new.
3. I replaced the actual entire Electonic Brake Control and proportion valve assembly (salvage from junkyard) This was a extremely difficult job that drove me NUTZ.
4. I checked all the lines for kinks and damage... none detected.

Here is what happens....

I begin to place the car in reverse and as it slowly gets up to speed (5 to 10 mph) the brake pedal tends to "creak and crunch" a little. As soon as I shift into drive the brake light comes on. The problem is NOT the actual sensor located in the E brake handle because if I lift it while driving the warning chime comes on. The stoplights both work so it cant be the brake pedal swith. I am just about ready to pay the stealership $100 to tell me what it is if somebody can't give me some more tech advice first.

Aaron, please help a felllow boost brother that has been denied cruise control ;crap. I would love to hear as many suggestions as possible. Thanks all!

AaronGTR
06-20-2011, 12:27 PM
Sounds to me like you've ignored the two most obvious things. All the mechanical stuff you've replaced like the master cylinder and ABS module... they have nothing at all to do with activating the brake lights. The only thing that sends a signal to activate them is the brake switch and the BCM.

I've had trouble in the past as well with my lights staying on. The problem was the pedal switch. There are actually two switches on the pedal under the dash. One activates the lights, and I'm not 100% sure what the function of the other one is. The one in the white plastic holder should be the lights. It's easy to tell if you have someone watch your tail lights and you push the switch in and out. Push it in, they go off, and out is on. There are a bunch of tiny slots in the switch cylinder and you are supposed to be able to push it forward or back in the holder to adjust the activation point then twist it to lock in place. I found that the plastic is very flimsy and doesn't like to hold and over time and use the switch works it's way loose. The brake pedal has some play in it and eventually while you are driving the switch will back off enough that the button is out far enough for the lights to activate. After re-adjusting mine 4 or 5 times I got sick of it and glued the SOB in place! lol

If it's not that switch, then it's most like a faulty BCM. Hope that solves the issue.

3800SII
06-20-2011, 12:52 PM
Sounds to me like you've ignored the two most obvious things. All the mechanical stuff you've replaced like the master cylinder and ABS module... they have nothing at all to do with activating the brake lights. The only thing that sends a signal to activate them is the brake switch and the BCM.

I've had trouble in the past as well with my lights staying on. The problem was the pedal switch. There are actually two switches on the pedal under the dash. One activates the lights, and I'm not 100% sure what the function of the other one is. The one in the white plastic holder should be the lights. It's easy to tell if you have someone watch your tail lights and you push the switch in and out. Push it in, they go off, and out is on. There are a bunch of tiny slots in the switch cylinder and you are supposed to be able to push it forward or back in the holder to adjust the activation point then twist it to lock in place. I found that the plastic is very flimsy and doesn't like to hold and over time and use the switch works it's way loose. The brake pedal has some play in it and eventually while you are driving the switch will back off enough that the button is out far enough for the lights to activate. After re-adjusting mine 4 or 5 times I got sick of it and glued the SOB in place! lol

If it's not that switch, then it's most like a faulty BCM. Hope that solves the issue.

I AM AN IDIOT... I should have been more specific because the problem is my dash BRAKE LIGHT and not the actual brake lights on the back of the car. Sorry for the confusion. Maybe you can take a look at my post and see if there is anything else that I can check! If there is a problem with the brake system then I do not have cruise control. Both the brake switch under the pedal and the cruise works

AaronGTR
06-20-2011, 04:19 PM
ah, gotcha. lol

That light could be caused by a bunch of other things there. If it's on, there should be a code stored in the BCM for it and they can read it with a tech2. That light is on in my grand prix also (as well as the traction/ABS lights) and I thought it was the typical faulty wheel speed sensor, but I had my dad take it to the dealer he works at and read the code and they said it was for an internal fault for the brake control module.

Some of those things it's best just to cough up the diagnostic fee and have the dealership check it out right away. The code can point you in the right direction before replacing a bunch of other stuff that's even more expensive and may not be the problem. ;)

As for what else to check, I'd say you replaced almost every mechanical component in the system already. All that's left is electrical stuff and it may well be an electrical fault. There is an actual ABS computer behind the washer fluid bottle behind the drivers side fender and it could be a problem with that since it's somewhat exposed to the elements. Only other thing left would be the BCM itself. I'd get the code read anyway just to be sure. If it's the BCM that needs replacing you'll have to take it to the dealer for reprogramming anyway so it would be easier if you're already there.

Malaclypse
06-20-2011, 07:33 PM
I bet you've got a wheel speed sensor problem. An erratic wheel speed sensor could cause that crunching noise you're talking about. Basically the EBCM is interpreting the signal wrong and things there's wheel slippage going on... so it goes into an ABS stop.

It'll help to get the code checked when the light is on. You HAVE to leave the car on when a code sets next time because once you turn the ignition off the code will be lost.

Another possibility is it may not set a code. You may have to have a technician drive the vehicle and watch all four wheel speed sensors with a scan tool to see which one is dropping out.

3800SII
06-20-2011, 09:36 PM
Thanks for all the replies! I can go ahead and check/ change the wheel hub assemblies, but I was always under the impression that a bad hub bearing will set an ABS/Trac/SVS light. It cant hurt to do that first.

I forgot that my HPT program does read BCM codes... Maybe I can scan the car myself and see if it is going haywire again.

3800SII
06-21-2011, 09:15 AM
I bet you've got a wheel speed sensor problem. An erratic wheel speed sensor could cause that crunching noise you're talking about. Basically the EBCM is interpreting the signal wrong and things there's wheel slippage going on... so it goes into an ABS stop.

It'll help to get the code checked when the light is on. You HAVE to leave the car on when a code sets next time because once you turn the ignition off the code will be lost.

Another possibility is it may not set a code. You may have to have a technician drive the vehicle and watch all four wheel speed sensors with a scan tool to see which one is dropping out.

Looky here what the HPT SCANNER uncovered:

C1232-LF WHEEL SPEED CIRCUIT OPEN OR SHORTED
C1275- HISTORY

C1225 LF EXCESSIVE WHEEL SPEED VARIATION (history current)
C1226 RF EXCESSIVE WHEEL SPEED VARIATION (history current)

The first two codes I have not seen before. I think that this is my issue.
The the third and fourth codes I have had for the longest even after I switched out the BCM, but no SVS light is on so I will ignore them for now.

I am going to jack up the car tonight and check the speed sensor/ replace the hub bearing if necessary. I will let you all know how it goes.

AaronGTR
06-21-2011, 08:46 PM
That's cool that the HPT scanner can check the BCM too. I wish DHP did that. There have been several times I wished I had a scanner for that (or just had an actual tech2).

SC/T02
06-22-2011, 10:10 AM
Glad you got things figured out!


On a side note
There have been several times I wished I had a scanner for that (or just had an actual tech2).

I love my Tech II scanner. Wife said I could have it or a S/C for the car (since they were only a few hundred dollars difference). This was the first time HP did not over rule application. I am so glad I have it. You can do just about ANYTHING to the car with it. When I changed gears and added a stall, I just changed it via the Tech II. So on and so forth. It has come in handy about 30 times so far. At the service rate and the charge for a scan at the dealer you can figure at least $100 per visit. So I have had about $3000 worth of use out of it in just 2.5 years.

3800SII
06-22-2011, 11:41 AM
Glad you got things figured out!


On a side note


I love my Tech II scanner. Wife said I could have it or a S/C for the car (since they were only a few hundred dollars difference). This was the first time HP did not over rule application. I am so glad I have it. You can do just about ANYTHING to the car with it. When I changed gears and added a stall, I just changed it via the Tech II. So on and so forth. It has come in handy about 30 times so far. At the service rate and the charge for a scan at the dealer you can figure at least $100 per visit. So I have had about $3000 worth of use out of it in just 2.5 years.

Lucky Bastard!:cheers: Too bad you don't live here in Memphis. I would have hit you up for a scan! I am sure that the Tech II has wayyyyy more parameters for many GM cars. At least you get your money worth.

On a followup, I did not get the chance to change the wheel bearing. I did take a good look at the left one, and it looks like it is in good shape. All the info on alldata leads me to belive that the problem is still elsewhere:

Conditions for Running the DTC
C1221 through C1228


DTCs C1232 through C1235 are not set.
The brake pedal is not pressed.
The ABS is not active.
C1232 through C1235
The ignition is ON.

Conditions for Setting the DTC
C1221 through C1224
There are two groups of conditions under which these DTCs could be set. In each group, all of the listed conditions must be met.
All of the following conditions exist for 2.5 seconds:


The suspect wheel speed equals zero.
The other wheel speeds are greater than 8 km/h (5 mph) .
The other wheel speeds are within 11 km/h (7 mph) of each other. Or, all of the following conditions exist for 20 seconds:
The suspect wheel speed and a second wheel speed both equal zero.
The remaining two wheel speeds are greater than 16 km/h (10 mph) .
The difference between the remaining two wheel speeds is less than 11 km/h (7 mph) .
C1225 through C1228
The EBCM detects a rapid variation in the wheel speed. The wheel speed changes by 16 km/h (10 mph) or more in 0.01 second. The change must occur 3 times with no more than 1 second between occurrences.

C1232 through C1235
One of the following conditions exists for 0.02 seconds:


A short to voltage - the wheel speed sensor signal circuit or the wheel speed sensor return circuit voltages are greater than 4.25 volts .
A short to ground - the wheel speed sensor signal circuit or the wheel speed sensor return circuit voltages are less than 0.75 volts .
An open - the wheel speed sensor signal circuit voltage is greater than 4.25 volts and wheel speed sensor return circuit voltage is less than 0.75 volts .
Action Taken When the DTC Sets
If equipped, the following actions occur:


The EBCM disables the ABS/TCS for the duration of the ignition cycle.
The EBCM temporarily suspends the TIM monitoring function while the DTC is set.
The ABS indicator turns ON.
The Traction Off indicator turns ON.
The DRP does not function optimally unless a DTC for the other wheel speed sensor on the same axle is also set, then the EBCM disables the DRP for the duration of the ignition cycle.
When the EBCM disables DRP, the red Brake warning indicator turns ON.
Conditions for Clearing the DTC


The condition for the DTC is no longer present and you used the scan tool Clear DTC function.
The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.
Diagnostic Aids
C1221 through C1224
Under the following conditions, 2 Wheel Speed Sensor Input is 0 DTCs are set:


The 2 suspect wheel speeds equal zero for 20 seconds.
The other wheel speeds are greater than 16 km/h (10 mph) .
The other wheel speeds are within 11 km/h (7 mph) of each other. Diagnose each wheel speed sensor individually.
C1225 through C1228
A possible cause of this DTC is electrical noise on the wheel speed sensor harness wiring. Electrical noise could result from the wheel speed sensor wires being routed to close to high energy ignition system components, such as spark plug wires.

C1232 through C1235
If the customer comments that the ABS indicator is ON only during moist environmental conditions: rain, snow, vehicle wash, etc., inspect the wheel speed sensor wiring for signs of water intrusion. If the DTC is not current, clear all DTCs and simulate the effects of water intrusion by using the following procedure:



Spray the suspected area with a 5 percent saltwater solution. To create a 5 percent saltwater solution, add 2 teaspoons of salt to 8 fl. oz. of water (10 g of salt to 200 ml. of water).
Test drive the vehicle over various road surfaces: bumps, turns, etc., above 40 km/h (25 mph) for at least 30 seconds.
If the DTC returns, replace the suspected wheel speed sensor or repair the wheel speed sensor wiring.
Rinse the area thoroughly when completed.
Test Description
The numbers below refer to the step numbers on the diagnostic table.


Measures the resistance of the wheel speed sensor in order to determine if the sensor has a valid resistance value.
Ensures that the wheel speed sensor is generating a valid AC voltage output.

3800SII
06-22-2011, 07:36 PM
I FOUND THE PROBLEM!! SOMEBODY WILL NEED TO STICKY THIS SOLUTION ANYTIME THEY HAVE AN ABS/TRAC/ BRAKE/ SVS DASH LIGHT MALFUNCTION.

This pisses me off, but at least I went through this issue TWICE in an effort to save others time and trouble.

Anytime you have these issues please do not immediately take your car to the dealership. Please go to the BCM location and remove all the paneling under the dash. Take off the connectors and look inside the BCM and connectors to see if you have a bunch of white and green corrosion (much like that you get on car batteries)

If you see a cluster of that then simply take some MassAirflow cleaner and spray all the connectors liberally. Make sure they are dry and take some dielectric grease to the inside prongs and connectors.Reinstall the unit, and chances are that your dash light issues will go away. If you reinstall the BCM after all this has been done, and issues still persist then you will need a new BCM. I was prepared to buy another used BCM, but I drove around the block and PRESTO! NO BRAKE LIGHT MALFUNCTION. My original BCM was replaced by a salvage unit after I had a persistent SVS/trac/ ABS malfunction. Same corrosion was present. The corrosion prevents the proper reference voltage signals to be sent from each switch or sensor, thus you get these stupid malfunctions....

My assumption is that GM decided not to use any type of electrical protectant because the BCM was inside the cabin. If you take a good look at the unit you can see that it is easily susceptible to moisture and corrosion. Most of us can see some type of rust on the retaining bar that bracets the BCM anyhow. Hell, for that matter the BCM is NOT SEALED, unlike the PCM modules for most GM cars. A little dielectric grease, and a better design casing would have been a good idea; however we all know that car repairs are all about $

There is no telling how many people got @$$ raped for a replacement unit thanks to lazy GM ingenuity. Simple, simple fix and solution....

Malaclypse
06-22-2011, 08:11 PM
^ The only issue I see with your findings on the BCM is that the BCM has absolutely nothing to do with the wheel speed sensors. The wheel speed sensors are wired directly to the EBCM which is under the hood. It's bolted to the side of the Brake Pressure Modulator Valve and is a totally sealed/weather-packed unit.

Those wheel speed sensor codes may have cleared for now but its possible or even likely that they'll come back.

I have seen the corrosion you speak of cause interesting electrical concerns like interior light problems or security issues, though. Its been awhile since I've seen any of them though. You're spot on about the BCM being in a bad place. Being under the HVAC case in the evaporator area doesn't help.

3800SII
06-22-2011, 08:36 PM
^ The only issue I see with your findings on the BCM is that the BCM has absolutely nothing to do with the wheel speed sensors. The wheel speed sensors are wired directly to the EBCM which is under the hood. It's bolted to the side of the Brake Pressure Modulator Valve and is a totally sealed/weather-packed unit.

Those wheel speed sensor codes may have cleared for now but its possible or even likely that they'll come back.
I have seen the corrosion you speak of cause interesting electrical concerns like interior light problems or security issues, though. Its been awhile since I've seen any of them though. You're spot on about the BCM being in a bad place. Being under the HVAC case in the evaporator area doesn't help.

Sounds like that great GM feeling :balla:

Yes, the EBCM it is totally sealed, but I disagree with you. On my first go around with this mess it was the simple change of the BCM that remedied the problems of a nagging SVS/ABS/Trac light problem. If you a saying that the EBCM is standalone from the BCM then I will have to verify that with the wiring diagrams in Alldata. FWIW, I already changed the EBCM with a salvaged unit, and the same codes were there before and after.

3800SII
06-22-2011, 08:58 PM
^ The only issue I see with your findings on the BCM is that the BCM has absolutely nothing to do with the wheel speed sensors. The wheel speed sensors are wired directly to the EBCM which is under the hood. It's bolted to the side of the Brake Pressure Modulator Valve and is a totally sealed/weather-packed unit.

Those wheel speed sensor codes may have cleared for now but its possible or even likely that they'll come back.

I have seen the corrosion you speak of cause interesting electrical concerns like interior light problems or security issues, though. Its been awhile since I've seen any of them though. You're spot on about the BCM being in a bad place. Being under the HVAC case in the evaporator area doesn't help.

I checked Alldata, but I could not find any schematics from the BCM or EBCM as to where they wire to. It makes me wonder why the problems stopped if what you are saying is correct.:confused:

Let me scan the car tomorrow and see what I find....

AaronGTR
06-22-2011, 09:42 PM
The data from the EBCM goes to the BCM, and the BCM relays signals to the dash cluster when it detects malfunctions. I don't have my manual handy right now so I can't look up to see which of the two is more directly responsible for determining faults, but I can tell you for certain that they work together and that the codes are set and stored in the BCM. I remember that from looking it up previously.

3800SII
06-23-2011, 05:00 AM
The data from the EBCM goes to the BCM, and the BCM relays signals to the dash cluster when it detects malfunctions. I don't have my manual handy right now so I can't look up to see which of the two is more directly responsible for determining faults, but I can tell you for certain that they work together and that the codes are set and stored in the BCM. I remember that from looking it up previously.

Thanks for verifying this Aaron! You da man! I did not think that I was that crazy.

Malaclypse
06-23-2011, 11:24 AM
I'll be the first to admit when I'm wrong... but this, no I am not.


Brake System Indicator

The IPC illuminates the brake indicator when the following occurs:

•The body control module (BCM) detects that the park brake is engaged. The IPC receives a class 2 message from the BCM indicating the park brake status. If the vehicle speed is greater than 5 km/h (3.1 mph) with the park brake engaged, the BCM sends a class 2 message to the radio in order to activate an audible warning.

• The electronic brake control module (EBCM) detects a low brake fluid condition (signal circuit is low). The IPC receives a class 2 message from the EBCM requesting illumination. The IPC sends a class 2 message to the BCM indicating that the brake indicator is illuminated due to a brake malfunction. The BCM sends a class 2 message to the radio in order to activate an audible warning.

• The EBCM detects a malfunction in the braking system. The IPC receives a class 2 message from the EBCM requesting illumination. The IPC sends a class 2 message to the BCM indicating that the brake indicator is illuminated due to a brake malfunction. The BCM sends a class 2 message to the radio in order to activate an audible warning.

• The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.

•The IPC detects a loss of class 2 communications with the EBCM.


ABS Indicator

The IPC illuminates the ABS indicator when the following occurs:

• The electronic brake control module (EBCM) detects a malfunction with the antilock brake system. The IPC receives a class 2 message from the EBCM requesting illumination. The IPC sends a class 2 message to the body control module (BCM) indicating that the ABS indicator is illuminated. The BCM sends a class 2 message to the radio in order to activate an audible warning.

• The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.

• The IPC detects a loss of class 2 communications with the EBCM.

3800SII
06-23-2011, 11:49 AM
I'll be the first to admit when I'm wrong... but this, no I am not.


Brake System Indicator

The IPC illuminates the brake indicator when the following occurs:

•The body control module (BCM) detects that the park brake is engaged. The IPC receives a class 2 message from the BCM indicating the park brake status. If the vehicle speed is greater than 5 km/h (3.1 mph) with the park brake engaged, the BCM sends a class 2 message to the radio in order to activate an audible warning.

• The electronic brake control module (EBCM) detects a low brake fluid condition (signal circuit is low). The IPC receives a class 2 message from the EBCM requesting illumination. The IPC sends a class 2 message to the BCM indicating that the brake indicator is illuminated due to a brake malfunction. The BCM sends a class 2 message to the radio in order to activate an audible warning.

• The EBCM detects a malfunction in the braking system. The IPC receives a class 2 message from the EBCM requesting illumination. The IPC sends a class 2 message to the BCM indicating that the brake indicator is illuminated due to a brake malfunction. The BCM sends a class 2 message to the radio in order to activate an audible warning.

• The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.

•The IPC detects a loss of class 2 communications with the EBCM.


ABS Indicator

The IPC illuminates the ABS indicator when the following occurs:

• The electronic brake control module (EBCM) detects a malfunction with the antilock brake system. The IPC receives a class 2 message from the EBCM requesting illumination. The IPC sends a class 2 message to the body control module (BCM) indicating that the ABS indicator is illuminated. The BCM sends a class 2 message to the radio in order to activate an audible warning.

• The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.

• The IPC detects a loss of class 2 communications with the EBCM.

Ok thanks Einstein... :applause: I couldn't find those diagrams.

It still doesn't quite add up to me because there have been many people that have replaced the BCM and not the EBCM for issues that I have stated. Is there not a wiring diagram of the BCM that shows what each wire is for? I am not trying to say that you are wrong and Aaron and I are correct, but there has to be some sort of correlation.

I am adamant concerning the fact that I replaced mine over 1 year ago, and all those issues stopped!

AaronGTR
06-23-2011, 02:54 PM
I'll look at the wiring diagrams in my manual again when I get a chance, but I'm pretty sure I remember everything going through the BCM before going to the IPC. Like I said though, I don't have the manual handy hear at home right now.

Malaclypse
06-23-2011, 06:17 PM
Ok thanks Einstein... :applause: I couldn't find those diagrams.

It still doesn't quite add up to me because there have been many people that have replaced the BCM and not the EBCM for issues that I have stated. Is there not a wiring diagram of the BCM that shows what each wire is for? I am not trying to say that you are wrong and Aaron and I are correct, but there has to be some sort of correlation.

I am adamant concerning the fact that I replaced mine over 1 year ago, and all those issues stopped!

The corrosion you mentioned could have been causing the BCM to turn the light on because it thinks the E-brake is engaged. That's very possible.

SC/T02
06-23-2011, 11:35 PM
^ Yeah Scott, but should'nt he hear the chime of that brake being on while in motion (the one that says idiot, you e-brake is on and your trying to drive)?