1996 Corvette Auto, 5.7 liter, ABS Light service is on, I have brakes, ABS fuse is good, Brake hydraulic fuse is good all wheel sensor wires appear to be attached and OK. Can you tell me where the ABS relay switch is located, I can by-pass the relay wiring and activate ABS pump motor and it is functioning. I have power to a relay located somewhere but not coming out to ABS pump

You need to find out what code is stored in the ABS control module, if the light is on there is a DTC an the system is disabled ! Don't know if auto part stores can pull ABS codes or not , You'll have to check it out . Personally I say take it to a ASE certified repair shop if you don't know anything about anti lock brakes !
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Electronic Brake Control Module (EBCM) -- The EBCM controls the system functions and detects failures.

The EBCM contains the following components:

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System Relays -- The inlet and outlet solenoid relay is energized when the ignition is ON and no ABS DTCs are present. It supplies battery positive voltage to the solenoid valves, the pump motor relay is energized and supplies battery positive voltage to the pump motor when ABS is activated.

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Brake Pressure Modulator Valve (BPMV) -- The BPMV contains the hydraulic valves and pump motor that are controlled electrically by the EBCM. The BPMV uses a 4 circuit configuration with a diagonal split. The BPMV directs fluid from the reservoir of the master cylinder to the left front and right rear wheels and fluid from the other reservoir to the right front and left rear wheels. The diagonal circuits are hydraulically isolated so that a leak or malfunction in one circuit will allow continued braking ability on the other.

This system can store 10-12 DTC's for something simple as wheel speed sensors to wiring problems to a malfunction of the EBCM . Some of these problems you would need a professional type scan tool ! The antilock brake system on your vehicle is the
BOSCH 8.0 antilock braking system
The vehicle is equipped with the following braking systems:
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Antilock Brake System (ABS)

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Dynamic Rear Proportioning (DRP)

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Traction Control System (TCS) (w/NW7)

The following components are involved in the operation of the above systems:
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Electronic Brake Control Module (EBCM) -- The EBCM controls the system functions and detects failures.

The EBCM contains the following components:

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System Relays -- The inlet and outlet solenoid relay is energized when the ignition is ON and no ABS DTCs are present. It supplies battery positive voltage to the solenoid valves, the pump motor relay is energized and supplies battery positive voltage to the pump motor when ABS is activated.

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Brake Pressure Modulator Valve (BPMV) -- The BPMV contains the hydraulic valves and pump motor that are controlled electrically by the EBCM. The BPMV uses a 4 circuit configuration with a diagonal split. The BPMV directs fluid from the reservoir of the master cylinder to the left front and right rear wheels and fluid from the other reservoir to the right front and left rear wheels. The diagonal circuits are hydraulically isolated so that a leak or malfunction in one circuit will allow continued braking ability on the other.

Important: There is a rubber isolator located under the BPMV and on the mounting studs. The rubber isolators protect the BPMV and the EBCM from vehicle vibrations.

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The BPMV contains the following components:

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Pump Motor

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Inlet Valves (one per wheel)

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Outlet Valves (one per wheel)

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Wheel Speed Sensors (WSS) -- As the wheel spins, the wheel speed sensor produces an AC signal. The EBCM uses this alternating current signal to calculate wheel speed. The wheel speed sensors are replaceable only as part of the wheel hub and bearing assemblies.

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Traction Control Switch (w/NW7) -- The TCS is manually disabled or enabled using the traction control switch.

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Stop Lamp Switch - The EBCM uses the stop lamp switch as an indication that the brake pedal is applied

the ABS is anti brake skid which is designed to stop wheel lock up under brakes and allow steering control at all times
it was originally designed for aircraft to stop the under carriage from being ripped from the plane when the wheels (under brakes on landing ) hit a wet patch , snow or ice on the runway
it works by each wheel having a segmented sender that is read by a sensor and this impulse switches on valves in the electric pump in the hydraulic system so that when the wheel stops turning ,brake pressure to that wheel is released momentarily and then reapplied when the wheel turns again
the person using the brake still feels the same brake pressure under the foot and in extreme situations will feel the brake pedal pulsate
Now the ECM continually monitors the ABS system and when fluid sensors, or electronic sensors fall outside set parameters , the ABS light comes on to let you know that there is a problem with the brakes
you should now be having the fault codes read to find the reason for the light and have it repaired as in some systems ,if the repairs are not effected then the vehicle is put into limp mode by the ECM and that reduces the power available and the speed of the vehicle.

First, check to see if your ABS and your TCS fuses are good. A lot of times, if both lights come on, it senses a failure in the braking system. Your vehicle will disable the abs if it finds a problem in the braking system, hence the red brake light/hand brake light coming on in the dash. Get a code scanner that also reads the abs module. You could have a bad wheel sensor, which is tied to your TCS and your ABS system. Either that, or you ABS module could be bad.

While it may be an eletrical issue developing, it may also be internal to the hydraulics of the brake system. If the system was recently flushed, I would look at the wheel sensors first- make sure thery have not picked up debris and sensors are snugly mounted and wiring in good shape.

If the brake system has not been flushed with new fluid, the system should get flushed out next time brakes are serviced. This may mean an expensive repair, but it depands on how comfortable and experienced you are without ABS at all.

If the ABS fails- all that happens is you lose the brake pressure modulation. Fancy word for braking yes- pulsing of the pedal by the system- no. The wheels or a single wheel "might" lock up while hard braking possibly changing handling dynamics of the vehicle..

Check Brake fluid level.

When the ABS light is on, the brakes should revert to standard braking.

The only time ABS should invoke is when the tires are slipping as sensed by the wheel speed sensors when the wheel locks up on any of the axles.
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ANTI-LOCK BRAKE SYSTEMS General Information Fig. 1: RWAL brake system diagram
Fig. 2:4WAL Component locations — except 1996 models
p>Fig. 3: 4WAL Component locations — 1996 models Fig. 4: Three sensor 4WAL brake system diagram — Except 1996 models
Fig. 5: Four sensor 4WAL brake system diagram — Except 1996 models
There are two basic types of anti-lock systems available for this vehicle; a Rear Wheel Anti-Lock (RWAL) brake system and 4 Wheel Anti-Lock (4WAL) brake system. The 4WAL system has two variations; a 3 sensor system and a 4 sensor system. The 2WD vehicles will be equipped with the 3 sensor system, but the AWD vehicles can be equipped with either. The systems are easily identified by looking at the rear wheels for a sensor harness. If there is a sensor harness and thus, rear wheel sensors, it is the 4 sensor system. If the vehicle is not equipped with a harness, it is the 3 sensor system. The 4 sensor system takes it speed references from each of the wheels. The 3 sensor system takes its speed references from each of the front wheels and the vehicle speed sensor located in the transmission (2WD) or the transfer case (AWD). The RWAL system components consist of the Vehicle Speed Sensor (VSS), the Electronic Control Unit (ECU), the isolation/dump valve and the Vehicle Speed Sensor Buffer (also known as the Digital Ratio Adapter). The ECU also receives signals from various brake switches. The 4WAL system components consist of the Electro-Hydraulic Control Unit (ECHU) valve (also known as the Brake Pressure Modulator Valve or BPMV), the wheel speed sensors, Vehicle Speed Sensor (VSS) on 3 sensor systems and the VSS Buffer.

it mean that a wheel sensor is not working properly
your car computer cannot get a proper wheel reading
you need to scan the code at your local garage that are equiped with a scan tool

You can test the wheel speed sensors by unhooking the connectors and put ohmeter test leads on the sensor terminals should read around 1100-1600 ohms also the connectors themselves were bad for wires breaking inside the insulation at the connectors from flexing when the wheel is turned back and forth..Note excessive wheel bearing noise from bad bearings have also been known for interferring with clean abs signal also causing abs codes good luck

I would pull the fuse for the ABS hydraulic pump and then put it back in and see what happens. Don't ever recall a pump running. Dealer may need to hook up scan tool for diagnostic fault codes, DTCs.



Principles of Operation
The ABS control module receives wheel speed readings from both front wheel speed sensors and the rear differential speed sensor, and processes this information to determine if an ABS event is necessary. The wheel speed sensor electrically senses each tooth of the ABS sensor indicators as it passes through the wheel speed sensor's magnetic field.
The ABS control module continuously monitors and compares the rotational speed of each wheel speed sensor indicator and, when it detects an impending wheel lock, modulates brake pressure to the appropriate brake caliper(s). This is accomplished by triggering the hydraulic control unit (HCU) to open and close the appropriate solenoid valves. Once the affected wheel returns to normal speed, the ABS control module returns the solenoid valves to their normal position, and normal (base) braking resumes.
The ABS control module is self-monitoring. When the ignition switch is turned to the RUN position, the ABS control module will do a preliminary electrical check, and at approximately 20 km/h (12 mph), the pump motor is turned on for approximately one-half second. Any malfunction of the ABS system will cause the ABS to shut off; normal power assisted braking, however, remains.
Inspection and Verification — Scan Tool Communications Check

1. Verify the customer concern by carrying out the Drive Cycle Test.

1. Visually inspect for obvious signs of mechanical and electrical damage.

Visual Inspection Chart Mechanical Electrical

• Parking brake cable
• Tire pressure
• Tire size or mismatched tires

• Blown fuse
• Central junction box (CJB):
  • fuse 23 (10A)
• Battery junction box
  • fuse 102 (50A)
• Connectors or connections
• Ground integrity
• Harness routing
• Wire chafing
• Circuitry open/shorted

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Anti-Lock Control The four-wheel anti-lock brake system (4WABS) consists of the following components:

• Anti-lock brake control module (2C265)
• Front anti-lock brake sensor (2C204)
• Front anti-lock brake sensor indicator (2C182)
• Hydraulic control unit (2C219)
• Rear anti-lock brake sensor (2C190)
• Rear anti-lock brake sensor indicator (2C189)
• Yellow ABS warning indicator

abs relay some times go bad

Almost nothing! ABS warning lights first require an ABS code scan to find a starting point for vehicle service. Most of the ones I scan have wheel speed sensor failures, but sometimes those failures are caused by the sensors becoming disconnected from the system. Sometimes road debris will break a sensor wire, socket or other component close to the wheel. 96 Taurus will have a sensor for each front wheel which requires sensor wiring to each wheel as well, find the sensor wire (it will be a twisted pair of wires running to the wheel hub) follow it to the hub and make sure it's connected, look at the sensor and make sure it's not damaged. Do this at each wheel. If it has 4 wheel antilock brakes, there will be a sensor at each rear wheel as well, check them all. If you decide to remove wheels, be sure to properly support the vehicle with safety stands before you get underneath the vehicle. A jack is NOT a safe support while any part of your body is in danger from being crushed by the vehicle. If you do remove wheels, do a thorough brake inspection while the wheels are off. Check the brake fluid level in the master cylinder, look for brake fluid leakage everywhere there are hydraulic lines or hoses, check the lining thicknesses of the disc brake pads and drum brake shoes. If you can't find an obvious mechanical failure, it's time for an ABS diagnostic. However if you find a visual sensor problem, and you successfully correct it, the ABS light will go off, after the system self test completes. Usually the system self test completes in 3 to 10 seconds. Here's another thing to keep in mind: The wheel speed sensors are sensitive enough to trigger the light due to a severely low tire. They also can detect a tire size mismatch so if you've replaced a tire lately pay attention to the size designations, they must match!