1991 MAZDA MIATA ABS

ANTI-LOCK BRAKE SYSTEM
1988-91 BRAKES Mazda Anti-Lock Brake System
DESCRIPTION
The Anti-Lock Brake System (ABS) control unit senses reductions in front and rear wheel speed, and modulates
hydraulic pressure to the brakes to prevent wheel lock-up. The ABS consists of a hydraulic unit, 4 wheel speed
sensors and sensor rotors, valve relay, motor relay, pump motor, and ABS control unit. An ANTI-LOCK
warning light is located on the instrument panel. See Fig. 1
thru Fig. 3 .
Fig. 1: Locating Motor Relay & Valve Relay

Courtesy of MAZDA MOTORS CORP.

1991 Mazda MX-5 Miata
ANTI-LOCK BRAKE SYSTEM 1988-91 BRAKES Mazda Anti-Lock Brake System

1991 Mazda MX-5 Miata
ANTI-LOCK BRAKE SYSTEM 1988-91 BRAKES Mazda Anti-Lock Brake System
Microsoft
Sunday, July 05, 2009 2:17:31 PMPage 1 © 2005 Mitchell Repair Information Company, LLC.
Microsoft
Sunday, July 05, 2009 2:17:36 PMPage 1 © 2005 Mitchell Repair Information Company, LLC.

Fig. 2: Locating ABS Components (RX7 Shown; Miata Similar)
Courtesy of MAZDA MOTORS CORP.
Fig. 3: Locating ABS Components (929)

Courtesy of MAZDA MOTORS CORP.
NOTE: For more information on brake system, see BRAKE SYSTEM article in the
BRAKES Section.

1991 Mazda MX-5 Miata
ANTI-LOCK BRAKE SYSTEM 1988-91 BRAKES Mazda Anti-Lock Brake System
Microsoft
Sunday, July 05, 2009 2:17:31 PMPage 2 © 2005 Mitchell Repair Information Company, LLC.

OPERATION
Under normal driving conditions, the anti-lock brake system functions as a standard brake system. When
vehicle speed reaches 3.8 MPH, the ABS system will diagnose pump motor by briefly operating motor. Pump
motor operation may be heard inside vehicle.
The Electronic Control Unit (ECU) controls ABS by detecting speed sensor signals and activating solenoid
valve in hydraulic unit. Control unit also controls pump motor and self-diagnostic function. If a problem in the
ABS system is detected, ABS system functions as a conventional brake system. The ANTI-LOCK brake
warning light will also come on.
With detection of wheel lock-up, short pedal pulsations, occurring in rapid succession, will be felt in brake
pedal and steering wheel. Vehicle body may also vibrate slightly. These conditions are normal. Pedal pulsation
will continue until there is no longer a need for anti-lock function or until vehicle is stopped.
ANTI-LOCK BRAKE SAFETY PRECAUTIONS
NEVER open a bleeder valve or loosen a hydraulic line while ABS is pressurized.
NEVER disconnect or reconnect any electrical connectors while ignition is on. Damage to ABS control
unit may result.
DO NOT attempt to bleed hydraulic system without first referring to the appropriate article.
Only use specially designed brake hoses/lines on ABS-equipped vehicles.
DO NOT tap on speed sensor components (sensor, sensor rings). Speed rings must be pressed, NOT
hammered into hubs. Striking these components can cause demagnetization or a loss of polarization,
affecting the accuracy of the speed signal returning to the ABS control unit.
DO NOT mix tire sizes. Increasing the width, as long as tires remain close to the original diameter, is
acceptable. Rolling diameter must be identical for all 4 tires. Some manufacturers recommend tires of the
same brand, style and type. Failure to follow this precaution may cause inaccurate wheel speed readings.
DO NOT contaminate speed sensor components with grease. Only use recommended anti-corrosion
coating.
When speed sensor components have been removed, ALWAYS check sensor-to-ring air gaps when
applicable. These specifications can be found in each appropriate article.
ONLY use recommended brake fluids. DO NOT use silicone brake fluids in an ABS-equipped vehicle.
When installing transmitting devices (CB's, telephones, etc.) on ABS-equipped vehicles, DO NOT locate
the antenna near the ABS control unit (or any control unit).
Disconnect all on-board computers, when using electric welding equipment. CAUTION: See ANTI-LOCK BRAKE SAFETY PRECAUTIONS below.
WARNING:Refer to appropriate Anti-Lock Brakes (ABS) article for description,
operation, depressurizing, testing, system bleeding, trouble shooting and
system service. Failure to depressurize ABS could lead to physical injury.

1991 Mazda MX-5 Miata
ANTI-LOCK BRAKE SYSTEM 1988-91 BRAKES Mazda Anti-Lock Brake System
Microsoft
Sunday, July 05, 2009 2:17:31 PMPage 3 © 2005 Mitchell Repair Information Company, LLC.

DO NOT expose the ABS control unit to prolonged periods of high heat (185°F/85°C for 2 hours is
generally considered a maximum limit).
BLEEDING BRAKE SYSTEM
For ABS hydraulic unit bleeding, see HYDRAULIC UNIT under REMOVAL & INSTALLATION.
BRAKE LINE BLEEDING SEQUENCE
(1)
DIAGNOSIS
ABS system can only be diagnosed using ABS Tester (0000-42-0010). See Fig. 13 . An Adapter Harness
(49N0-66-001) is also required to test Miata ABS system. ABS tester cannot diagnose ABS control unit. If a
malfunction is detected in ABS and all other components in brake system are okay, replace ABS control unit.
If ABS tester is unavailable, test each component of ABS. See test procedures under TESTING. If all ABS
components test okay, replace control unit with a known good unit, and retest system for correct operation.
PRE-DIAGNOSIS INSPECTION
Perform a visual inspection of ABS components that could cause anti-lock problem. Visual inspection may help
identify cause of simple problem.
DIAGNOSTIC PROCEDURE WITH ABS TESTER
ABS tester uses one display window and 2 switches for reading information from unit. Become thoroughly
familiar with ABS tester displays and operation before proceeding. See Fig. 13
. To diagnose ABS system, go
to TESTING SEQUENCE charts under DIAGNOSING ABS SYSTEM. When diagnosing ABS system,
complete tests in order given under TESTING SEQUENCE. If ABS tester does not operate, check fuses,
ignition switch and ignition circuit.
TESTING
NOTE: See BRAKE BLEEDING article in the BRAKES Section.
ApplicationSequence
Miata & 929Longest Line First
RX7RR, LR, RF, LF
(1)If rear caliper has not been disassembled, open upper bleed valve only.
NOTE: Before testing ABS components, ensure battery and charging system are
functioning properly. To prevent damage to ABS control unit connector, use
very thin pins when probing connector.

1991 Mazda MX-5 Miata
ANTI-LOCK BRAKE SYSTEM 1988-91 BRAKES Mazda Anti-Lock Brake System
Microsoft
Sunday, July 05, 2009 2:17:31 PMPage 4 © 2005 Mitchell Repair Information Company, LLC.

ABS DIODE
Continuity Test
1. Unplug hydraulic unit 12-pin connector. On Miata, connect positive lead of DVOM to Blue/Yellow wire
terminal and negative lead to Gray wire terminal of hydraulic unit. On RX7, connect positive lead of
DVOM to Red wire terminal and negative lead to Yellow/Red wire terminal of hydraulic unit.
2. On 929, connect positive lead of DVOM to Violet wire terminal and negative lead to Yellow/Red wire
terminal of hydraulic unit. Ensure continuity is present between terminals. Reverse DVOM leads.
Continuity should not be present with leads reversed. If ABS diode does not test as described, replace
ABS diode.
ABS SYSTEM GROUND
Continuity Test (Miata)
Using a DVOM, check for continuity between terminals "D", "S", and "f" of control unit harness connector and
ground. See Fig. 4
or Fig. 5 . If continuity is not present, repair harness.
Continuity Test (RX7 & 929)
Use DVOM to check continuity. ON RX7, check between control unit harness connector terminal "D" and JC-
02 connector. See Fig. 4
and Fig. 6 or Fig. 5 and Fig. 7 . On 929, check between control unit harness connector
terminal "T" and JC-02 connector. If continuity is not present, repair harness.

1991 Mazda MX-5 Miata
ANTI-LOCK BRAKE SYSTEM 1988-91 BRAKES Mazda Anti-Lock Brake System
Microsoft
Sunday, July 05, 2009 2:17:31 PMPage 5 © 2005 Mitchell Repair Information Company, LLC.

Fig. 10: Testing ANTI-LOCK Warning Light (929)
Courtesy of MAZDA MOTORS CORP.
STOPLIGHT SWITCH
Continuity Test
Disconnect stoplight switch connector. Using a DVOM, check continuity between Green or Green/White wire
and White/Green wire with brake pedal depressed. Ensure continuity exists. Release pedal, and note reading on
DVOM. Continuity should not be present. If continuity is not as specified, replace switch.
FRONT & REAR VALVES
Resistance Test (Miata)
1. Disconnect hydraulic unit 12-pin connector. Using a DVOM, measure resistance between the following
wires: Yellow/Green wire and Black wire; Brown wire and Black wire; Black/White wire and Black wire.
Resistance should be 1-1.2 ohms in each measurement.
2. If resistance is not as specified, replace hydraulic unit. If resistance is as specified, check wiring harness
between ABS control unit and hydraulic unit.
Resistance Test (RX7 & 929)

1991 Mazda MX-5 Miata
ANTI-LOCK BRAKE SYSTEM 1988-91 BRAKES Mazda Anti-Lock Brake System
Microsoft
Sunday, July 05, 2009 2:17:31 PMPage 11 © 2005 Mitchell Repair Information Company, LLC.

1. Disconnect hydraulic unit 12-pin connector. Using a DVOM, measure resistance between Green/Black
and Yellow/Red wires, Green/White and Yellow/Red wires and Yellow and Yellow/Red wires.
Resistance should be 1-1.2 ohms in each measurement.
2. If resistance if not as specified, replace hydraulic unit. If resistance is as specified, check wiring harness
between ABS control unit and hydraulic unit.
HYDRAULIC UNIT
Only serviceable parts of hydraulic unit are motor relay and valve relay. If other parts of unit malfunction,
replace hydraulic unit assembly.
MOTOR RELAY
Continuity Tests
1. Disconnect negative battery cable. Remove motor relay from hydraulic unit. Ensure continuity exists
between terminals "B" and "C" of motor relay. See Fig. 11
. Connect 12 volts to terminal "C", and ground
terminal "B". Ensure continuity exists between terminals "A" and "D".
2. Replace relay if continuity is not as specified. If continuity is as specified, check wiring harness between
motor relay and ABS control unit fuse (60 amps).
Fig. 11: Identifying Motor & Valve Relay Terminals

Courtesy of MAZDA MOTORS CORP.
PUMP MOTOR
Continuity Test (Miata)

1991 Mazda MX-5 Miata
ANTI-LOCK BRAKE SYSTEM 1988-91 BRAKES Mazda Anti-Lock Brake System
Microsoft
Sunday, July 05, 2009 2:17:32 PMPage 12 © 2005 Mitchell Repair Information Company, LLC.

Disconnect 2-pin connector at hydraulic unit. Check continuity at hydraulic control between Red/Yellow wire
terminal and ground. If continuity is not present, replace hydraulic control unit. If continuity is present, pump is
okay. Check wiring between hydraulic control and ABS control unit.
Continuity Test (RX7 & 929)
1. Disconnect 12-pin hydraulic unit connector. Using a DVOM, check continuity between Black wire and
ground. If there is continuity, check continuity between Black wire terminal at hydraulic unit connector
and Green wire terminal at 2-pin hydraulic unit connector.
2. If continuity exists, connect hydraulic unit connectors. If continuity is not present, replace wiring harness
between control unit and body ground.
3. Disconnect ABS control unit connector. Check continuity between Green wire of ABS control unit
harness connector and ground. If continuity is present, check for poor connection of ABS control unit
connector or faulty ABS control unit. If continuity is not present, repair open circuit.
VALVE RELAY
Continuity Tests
1. Disconnect negative battery cable. Remove valve relay from hydraulic unit. Using a DVOM, check
continuity between relay terminals "C" and "E" and between terminals "B" and "D". See Fig. 11
.
2. Ensure continuity exists. Connect 12 volts to terminal "B", and ground terminal "D". Check continuity
between terminals "A" and "E". Ensure continuity exists. If continuity is not as specified, replace valve
relay.
WHEEL SPEED SENSORS
Sensor Resistance Test
Disconnect speed sensor connector. Using a DVOM, measure resistance between sensor terminals. Resistance
should be 800-1200 ohms. If resistance is not as specified, replace speed sensor.
Harness Continuity & Voltage Tests
1. With ignition off and speed sensors connected, disconnect ABS control unit connector. Using a DVOM,
check continuity between indicated terminals of ABS control unit harness connector. See WHEEL
SPEED SENSOR TESTS TABLE.
2. If reading on DVOM is not 800-1200 ohms, check wiring harness between wheel speed sensor and ABS
control unit. If DVOM reading is 800-1200 ohms, check voltage between indicated terminals in WHEEL
SPEED SENSOR TESTS TABLE.
3. Turn ignition on. Rotate appropriate wheel one revolution per second by hand to check voltage. If DVOM
does not indicate 50-60 millivolts, replace wheel speed sensor.
WHEEL SPEED SENSOR TESTS
Test Between Control Unit

1991 Mazda MX-5 Miata
ANTI-LOCK BRAKE SYSTEM 1988-91 BRAKES Mazda Anti-Lock Brake System
Microsoft
Sunday, July 05, 2009 2:17:32 PMPage 13 © 2005 Mitchell Repair Information Company, LLC.