In-Dash Brake Light Flashing

[Forscythe87]

Just started yesterday, the brake light that comes on when the E-Brake is applied started coming on. It stays on for almost a minute than goes off.

I didnt think it would come on for any other reason than having the E applied.

[Bearwulf]

Air bubble or sediment in proportioning valve can cause this also.

[Forscythe87]

Its now staying on a lot more. Could this possibly be low brake fluid? I'm afraid to drive at the moment. Dont wanna be driving down the highway and have no brakes.

[4x4 blazerguy]

My wife's 93 Lumina did that, it would flash. It was a bad connection to the ABS senor on the rear wheel. It could be any wheel though. If it is flashing then holding on it is most likely a sensor on the ABS system.

[cadgear]

Check the fluid level first, if it's not low then it could just be the sensor. Another thing to check would be the parking brake pedal, sometimes the connection gets kicked loose by enthusiastic parking.

Failing that, I'd bleed the system to remove any air or gunk. If you have ABS, go have it done, don't mess with the ABS module in any way.

[Blue Bowtie]

There are some things you can do and/or check without an ABS-capable scan tool,and some which will require the bi-directional communicating tool:

On initial ignition power-up, the fuel pump should cycle for about two seconds, but the ABS motor should also cycle briefly (and rather quietly). It's harder to hear the ABS motor run when starting the engine.

A few different scenarios may prevent the ABS motor from running:

• The lack of system power from the main relay will obviously stop the motor.
• A shorted or grounded wheel speed sensor circuit may stop the motor.
• An open or grounded brake pedal switch circuit can stop the motor.
• An open or grounded motor circuit or solenoid coil (or circuit) can set a fault code and prevent the motor from running.
• Some other hard fault codes in the EBCM can prevent motor running on power up.

SYSTEM POWER
There is a master ABS power relay and a pump motor relay in most installations. The main power relay is frequently located under the hood, inside the Underhood Electrical Center. (Older vehicles mounted the relay adjacent to the ABS hydraulic modulator unit.) The inside of the UEC cover should have a label indicating which relay is where. If you examine adjacent relays, you can often find another with the same part number and can swap them to see if that makes a difference. If the "other" device works but the ABS does not, chances are the relay was good. The EBCM operates the relay to provide main motor and solenoid power to the ABS modulator unit. One other check you can perform is to assure that battery voltage is present at the NO relay contact in the socket for the ABS relay. Obviously, lack of voltage there would interfere with ABS operation.

SENSOR INPUTS
Metering the sensors and wire harnesses at each wheel is easiest, and will reveal the condition of both the sensor signal level and wire harness. With the ignition off, you can check resistance to ground on the sensor harness wires to help reveal any cuts of other harness damage. With the ignition ON, and if the EBCM is powered, you should be able to measure a DC bias voltage across the two harness wires, but I'm not certain what that voltage is.

OTHER INPUTS
Check the fluid level switch, even of the red BRAKE warning lamp is not on. There are probably two sets of contacts in the switch, one N.O. and one N.C. to indicate switch position. The N.C. contacts are typically used to signal the EBCM whether fluid level is correct, and an open circuit here from a wiring problem or defective switch will not necessarily cause the red brake warning lamp to turn on.

Check the brake pedal arm switch for continuity. You may also want to insure that the center, high mounted brake lamp is working, since that can affect other systems on the vehicle, such as the cruise function and possibly the ABS.

OUTPUTS
There is at least one main valve solenoid on the ABS modulator unit, and up to six control valve solenoids. Disconnect the electrical connector and check the resistance of the solenoid coil windings one at a time , then the coil resistance to a good ground. The coils should present about 2-5 ohms through the coil, and show infinite resistance to ground. You can also test the solenoid coil wire harness for grounding if the ignition power is off.

There are many more checks which can be performed, but those get rather involved and nearly require a scanner.

MISCELLANEOUS PROBLEMS
I'm not positive on the '97-98 Lumina, but the EBCM is likely located mounted in the left front fender area near the ABS modulator. It's probably easier to access by removing the inner wheel opening splash shield, but you may want to save that job for later since there will be little you can do there without a scanner. One problem with that mounting location is that acidic battery fluid can drip or be washed down onto the module and create a lot of corrosion at the connections. Additional road spray can also find its way to the module.

Another, more obscure problem which can occur with this EBCM is a supply voltage problem caused by a failing alternator. If a rectifier in the alternator bridge is breaking down and allowing some reverse current flow, some AC voltage can be present in the system. Even relatively low levels of AC voltage can interfere with EBCM operation and inexplicably set error codes. You can test the output of the alternator directly at the output stud for AC voltage over 0.2VAC. At that level, problems can occur. Obviously, that is not likely the problem unless a hard code in EBCM history is causing the unit to shut down on power-up, since there should be nothing but clean DC voltage from the battery in a KOEO situation.