Brake light and ABS light stay "ON"

[jeffreypca]

I have a 96' Lumina, I have checked the e-brake and e-brake switch, they are fine, I checked for power to all wheel sensors. I even tried taking out the 2 fuses and the relay for the ABS and still will not go out.

I heard about the low fluid sensor, is there a way to bypass to check??
I tried just unplugging it, still lights on.

I can only think of the module, but I think the module is mounted on the
splitter under the hood.

Other than hooking up to diagnostic machine, any ideas of what else it could be???

I don't care about the abs myself but I am selling the car.

[twistedtech]

1. Why not get it scanned? You can't find an honest tech? I guess I must be a freak. I have spent 23 years trying to dispell the mechanic thief issue.If you want the codes out of your car I would give them to you. Prob is a speed sensor.
2. Why sell a car to somebody with a brake issue? Not cool.

[jeffreypca]

I am getting scanned on Tuesday, will find out I hope.

[Blue Bowtie]

Disconnecting the fluid level sensor will not help, since the sensor needs to complete the circuit to turn the light off, not the other way around.

Having both the ABS and BRAKE warning lamps on could indicate several things. Scanning is an easy way to find out, but since you have a couple days, check the ABS power fuse or fusible link, the ABS power relay, wheels sensor signals, and brake pedal switches.

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.

[jeffreypca]

Should there be voltage going to the fluid level sensor???

[jeffreypca]

It also has a loud tick in the dash, lick a solinoid sound, when I press the brake peddle, did that when I bought it too.

[Blue Bowtie]

The clicking in the dash may actually be in the steering column. There is a solenoid used to release the shift (park) interlock when the brake pedal is depressed. Those circuits are independent of the EBCM and ABS system.

The master cylinder fluid level sensor will have two signals. It's best to unplug the level switch and measure switch continuity rather than the power.

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.