1991 MAZDA MIATA sensor

Fig. 12: Checking Impact Sensor Resistance
Courtesy of MAZDA MOTORS CORP.
DIAGNOSTIC TEST NO. 4
Warning Light Flashes 10 Times
1. Disable air bag system. See DISABLING & ACTIVATING AIR BAG SYSTEM. Disconnect front
impact sensor connectors (center, left, and right), and measure resistance of each sensor. See Fig. 12
.
Resistance should be approximately 1.2 k/ohms. If resistance is not as specified, replace sensor and go to
step 5).
2. If resistance is about 1.2 k/ohms, reconnect all front impact sensor connectors. Disconnect diagnostic
module Black and Gray connectors. See Fig. 10
or Fig. 11 . Measure resistance between diagnostic
module Gray connector Brown/Green wire and ground. If resistance is 1.2 k/ohms, go to next step. If
resistance is not 1.2 k/ohms, replace wire harness.
3. Measure resistance between diagnostic module Gray connector Brown/Red wire and ground. If resistance
is 1.2 k/ohms, go to next step. If resistance is not 1.2 k/ohms, replace wire harness.
4. Measure resistance between diagnostic module Black connector Brown/Black wire and ground. If
resistance is 1.2 k/ohms, go to next step. If resistance is not 1.2 k/ohms, replace wire harness and go to
next step.
5. If disconnected, reconnect dia
gnostic module and clockspring connectors. Reconnect negative battery

1991 Mazda MX-5 Miata
AIR BAG RESTRAINT SYSTEM MAZDA 1990-91 AIR BAGS
Microsoft
Sunday, July 05, 2009 2:11:16 PMPage 19 © 2005 Mitchell Repair Information Company, LLC.

cable. Turn ignition switch to ON position and check warning light operation. If warning light flashes 10
times, replace diagnostic module.
DIAGNOSTIC TEST NO. 5
Warning Light Flashes 4 Times
1. Disable air bag system. See DISABLING & ACTIVATING AIR BAG SYSTEM. Disconnect diagnostic
module Black and Gray connectors. See Fig. 10
or Fig. 11 . Check continuity between Black connector
Green/White wire terminals. If continuity is not present, replace wire harness.
2. If continuity is present, check continuity between Black connector Green wire and ground (1990 Miata),
or between Gray connector Red/Black wire terminal and ground (all others). If continuity is not present,
go to step 4). If continuity is present, check continuity between Black connector Green wire terminal and
Gray connector Green/Black wire terminal. If continuity is present, go to step 4) (1990 Miata), or step 5)
(all others).
3. If continuity is not present, disconnect rear safing sensor connectors. Check continuity between sensor
terminals "B" and "E". See Fig. 13
. If continuity is present, replace wire harness. If continuity is not
present, replace rear safing sensor.
4. Check rear safing sensor installation; repair as necessary. If installation is okay, disconnect rear safing
sensor connectors. Check continuity between sensor terminal "A" and ground. If continuity is not present,
replace rear safing sensor. If continuity is present, replace wire harness.
5. Disconnect diagnostic connector. Check continuity between Black connector Green/White wire and
ground. If continuity is present, replace wire harness. If continuity is not present, repeat step 4).

1991 Mazda MX-5 Miata
AIR BAG RESTRAINT SYSTEM MAZDA 1990-91 AIR BAGS
Microsoft
Sunday, July 05, 2009 2:11:16 PMPage 20 © 2005 Mitchell Repair Information Company, LLC.

Fig. 13: Identifying Rear Safing Sensor Terminals
Courtesy of MAZDA MOTORS CORP.
DIAGNOSTIC TEST NO. 6
Warning Light Flashes 6 Times
1. Disconnect negative battery cable. Check connection of Orange/Blue clockspring connector; repair as
necessary.
2. If connection is okay, disconnect air bag module and clockspring connector. Check continuity, as shown
in illustration, for both terminals of Blue side of clockspring connector. See Fig. 14
. If continuity is not
present, replace Oran
ge/Blue clockspring connector.

1991 Mazda MX-5 Miata
AIR BAG RESTRAINT SYSTEM MAZDA 1990-91 AIR BAGS
Microsoft
Sunday, July 05, 2009 2:11:16 PMPage 21 © 2005 Mitchell Repair Information Company, LLC.

2. Check continuity between Black connector Brown/White wire and ground. If continuity is not present, go
to step 5). If continuity is present, go to next step.
3. Check continuity between Black connector Brown wire and ground. If continuity is present, replace
diagnostic module. If continuity is not present, go to step 6).
4. Disconnect right front impact sensor connector. Check continuity between ground and each harness
sensor terminal. See Fig. 15
. If continuity is present, replace wire harness assembly. If continuity is not
present, go to step 7).
Fig. 15: Checking Continuity at Right Front Impact Sensor Connector

Courtesy of MAZDA MOTORS CORP.
5. Disconnect center front impact sensor connector. Check continuity between ground and each harness
sensor terminal. If continuity is present, replace wire harness assembly. If continuity is not present, go to
step 7).
6. Disconnect left front impact sensor connector. Check continuity between ground and each harness sensor
terminal. If continuity is present, replace wire harness assembly. If continuity is not present, go to step 7).
7. Ensure all front impact sensors are correctly installed. If all front impact sensors are installed correctly,
replace defective front impact sensor.
DIAGNOSTIC TEST NO. 8

1991 Mazda MX-5 Miata
AIR BAG RESTRAINT SYSTEM MAZDA 1990-91 AIR BAGS
Microsoft
Sunday, July 05, 2009 2:11:16 PMPage 23 © 2005 Mitchell Repair Information Company, LLC.

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.

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.

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.

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
Microsoft
Sunday, July 05, 2009 2:17:32 PMPage 14 © 2005 Mitchell Repair Information Company, LLC.