1991 MAZDA MIATA Factory Service Manual

1. Start engine, and observe ANTI-LOCK light. Light should illuminate for a few seconds. If light does not
illuminate as described, remove clock and bezel assembly from dashboard. Slide warning and clock unit
from instrument panel. Connect terminal "E" to ground. See Fig. 9
. ANTI-LOCK light should illuminate.
If light does not illuminate, check bulb. If bulb is okay, check meter fuse and wiring harness.
2. Install instrument cluster, and recheck warning light operation. If light still does not illuminate for a few
seconds, check wiring harness between ANTI-LOCK light and control unit, and ANTI-LOCK light and
hydraulic unit. Check operation of hydraulic unit valve relay.
Operational Test (929)
1. Start engine, and observe ANTI-LOCK light. Light should illuminate for a few seconds. If light does not
illuminate as described, remove instrument cluster. Connect 12 volts to terminal "J" of instrument cluster
connector I-06. See Fig. 10
. Using a jumper wire, connect terminal "E" of instrument cluster connector I-
08 to negative ground. ANTI-LOCK light should illuminate. If light does not illuminate, check bulb. If
bulb is okay, check meter fuse and wiring harness.
2. Install instrument cluster, and recheck warning light operation. If light still does not illuminate for a few
seconds, check wiring harness between ANTI-LOCK light and control unit and between ANTI-LOCK
light and hydraulic unit. Check operation of hydraulic unit valve relay.
Fig. 8: Testing ANTI
-LOCK Warning Light (Miata)
Courtesy of MAZDA MOTORS CORP.

1991 Mazda MX-5 Miata
ANTI-LOCK BRAKE SYSTEM 1988-91 BRAKES Mazda Anti-Lock Brake System
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Fig. 9: Testing ANTI-LOCK Warning Light (RX7)
Courtesy of MAZDA MOTORS CORP.

1991 Mazda MX-5 Miata
ANTI-LOCK BRAKE SYSTEM 1988-91 BRAKES Mazda Anti-Lock Brake System
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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
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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
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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
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WHEEL SPEED SENSOR ROTORS
Inspection
Perform a comprehensive visual inspection of sensor rotor. If any damage is noted, replace sensor rotor. Sensor
rotors are attached to wheel hubs.
REMOVAL & INSTALLATION
HYDRAULIC UNIT
Removal
Remove hydraulic lines from unit. Disconnect hydraulic unit connectors. Remove nuts securing unit. Remove
hydraulic unit.
Bleeding Hydraulic Unit
Before bleeding hydraulic unit, bleed brake system in appropriate sequence. See BRAKE LINE BLEEDING
SEQUENCE TABLE under BLEEDING BRAKE SYSTEM. Bleed hydraulic unit by opening bleeder screw on
unit. See Fig. 12
.
Installation
To install, reverse removal procedure. Tighten mounting bolts to specification. See TORQUE
ApplicationConnector Terminals (1)
Miata
Left Front"K" & "G"
Left Rear"O" & "Q"
Right Front"U" & "F"
Right Rear"L" & "P"
RX7
Left Front"D" & "F"
Left Rear"H" & "I"
Right Front"U" & "W"
Right Rear"X" & "Z"
929
Left Front"K" & "G"
Left Rear"O" & "Q"
Right Front"J" & "F"
Right Rear"L" & "P"
(1)See Fig. 4 or Fig. 5 to identify ABS control unit terminals.

1991 Mazda MX-5 Miata
ANTI-LOCK BRAKE SYSTEM 1988-91 BRAKES Mazda Anti-Lock Brake System
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SPECIFICATIONS TABLE at end of article.
Fig. 12: Locating Hydraulic Unit Bleeder Screw

Courtesy of MAZDA MOTORS CORP.
WHEEL SPEED SENSOR ROTOR
Removal (Miata)
Remove brake caliper. Remove wheel hub. On rear axle, carefully remove sensor rotor from axle using a chisel.
On front rotor, remove sensor rotor using Puller (49- 0839-425C).
Installation
Press sensor rotor onto axle using Installer (49- H026-101A). Install sensor rotor on front rotor with chamfered
edge toward hub using Press Adapter (49-F001-95). To complete installation, reverse removal procedure.
Tighten mounting bolts to specification. See TORQUE SPECIFICATIONS TABLE at end of article.
Removal & Installation (RX7)
Remove brake caliper and wheel hub. On rear hub, remove wheel hub from outer toe control hub using Puller
(49-F026-103) and Installer (49-F026-102). On front rotor, remove rotor-to-hub bolts using Allen wrench. On
rear rotor, remove rotor-to-hub screws. To install, reverse removal procedure. Tighten mounting bolts to
specification. See TORQUE SPECIFICATIONS TABLE at end of article.
Removal & Installation (929)

1991 Mazda MX-5 Miata
ANTI-LOCK BRAKE SYSTEM 1988-91 BRAKES Mazda Anti-Lock Brake System
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Remove brake caliper and wheel hub. On rear axle, carefully remove sensor rotor from axle using chisel. On
front rotor, remove sensor rotor using Puller (49-0839-425C). To install, press sensor rotors onto axle and front
rotor using Installer (49-H026-101A). On front rotor, install sensor rotor with chamfered edge toward hub. To
complete installation, reverse removal procedure. Tighten mounting bolts to specification. See TORQUE
SPECIFICATIONS TABLE at end of article.
WHEEL SPEED SENSOR
Removal & Installation
Unplug wheel sensor connector. Remove sensor bolt. Remove wheel sensor from vehicle. To install, reverse
removal procedure. On RX7, adjust wheel sensor so clearance between sensor and rotor is .016-.039" (.40-1.0
mm). Tighten mounting bolts to specification. See TORQUE SPECIFICATIONS TABLE at end of article.
DIAGNOSING ABS SYSTEM
ABS TESTER OPERATION
Fig. 13: Operating ABS Tester

Courtesy of MAZDA MOTORS CORP.
TESTING SEQUENCE

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