DESCRIPTION
The Mazda power steering system is a hydraulically assisted rack and pinion type. This steering system changes its steering assist power according to information received from the vehicle speed sensor, turning angle sensor (steering wheel), and engine speed sensor. A control unit receives signals from all of these sensors and will regulate the proper amount of hydraulic pressure needed by rotating an electric stepping motor or operating an electric solenoid.
Control unit contains self-diagnostic capabilities for all electrical steering components. It also includes a fail-safe function that if for any reason, no signal is received from vehicle speed sensor, signal from engine speed sensor would be detected, and hydraulic pressure would be regulated based upon that signal.
Scheme 6
FAIL-SAFE SYSTEM
The Mazda electronically controlled power steering system incorporates several fail-safe systems designed to maintain vehicle control under a wide variety of possible power steering malfunctions.
MX-6 & 626
- If an engine speed malfunction occurs, the control unit will read the vehicle speed input and normal function will occur.
- If the vehicle speed sensor malfunctions, the control unit will seek an engine speed signal of 2200 RPM for 30 seconds. If this signal is present and vehicle speed is below 50 MPH (80 KPH), steering effort will be set at the 50 MPH (80 KPH) level. If the vehicle speed is above 50 MPH (80 KPH), the steering effort level will be maintained at level at which failure occured.
- If the steering angle sensor malfunctions and the vehicle speed is greater than 25 MPH (40 KPH) with a continuous steering angle of 35+ degrees for more than 80 seconds, steering effort will be decreased slightly at speeds above 25 MPH (40 KPH).
- If the stepping motor, control unit or electrical circuit malfunctions, the steering effort will be adjusted to a 50 MPH (80 KPH) level.
RX7
- If engine-speed sensor malfunctions, vehicle speed signal will be input to computer even if engine speed signal is not. Power steering will be controlled normally.
- If vehicle speed sensor malfunctions and vehicle speed is below 50 MPH or engine speed is above 2200 RPM, steering effort is adjusted as if vehicle speed is above 50 MPH. If vehicle speed is above 50 MPH or engine speed is less than 2200 RPM, steering effort is adjusted to speed last sensed when failure occurred.
- If steering angle sensor malfunctions with vehicle speed more than 25 MPH and more than 35 degrees of steering angle for over 80 seconds, steering effort is slightly decreased at all speeds above 25 MPH.
- If malfunction of control unit or stepping motor output occurs, power supply to stepping motor is cancelled and steering effort is adjusted as if vehicle speed is 50 MPH.
929
- If vehicle speed sensor malfunctions while driving, the steering effort will remain the same as at the time of the malfunction. If the vehicle speed sensor malfunctions at idle or while the vehicle is stationary, the power steering will be activated when engine speed reaches 2370 RPM.
- If the engine RPM sensor or circuit malfunctions, power steering effort will be determined by vehicle speed.
- If the control valve malfunctions or has an electrical circuit failure, steering effort will be heavy.
- If the steering angle sensor or control unit malfunctions, steering effort will be heavy.
TESTING
Note. For more information on wiring diagrams, see appropriate SUSPENSION - ELECTRONIC article
Solenoid Valve Test
Disconnect solenoid connector. Using an ohmmeter, measure the resistance of the solenoid valve. Resistance should be 3.4-6.9 Ohms. Apply 12 volts to one connector lead and ground the other. Solenoid should operate with a noticeable sound. Replace solenoid if there is no continuity or solenoid does not operate.
Scheme 7
Diagnostic Code Access
To access the self diagnostic codes, connect a voltmeter between test connector wire "YB" and ground. Diagnostic codes are displayed as voltage output pulses. Test system under following conditions, record diagnostic codes and compare to 626 & MX-6 DIAGNOSTIC CHARTS. (Scheme 8)
Condition "A"
Turn ignition switch to "OFF" position. Start engine and allow to idle. Turn steering wheel to straight ahead position and check output pulses. If pattern is not normal, compare to 626 & MX-6 DIAGNOSTIC CHARTS. (Scheme 8)
Condition "B"
Turn ignition switch to "OFF" position. Start engine and allow to idle. Turn steering wheel 45 degrees to right and check output pulses. If pattern is not normal, compare to 626 & MX-6 DIAGNOSTIC CHARTS. (Scheme 8)
Condition "C"
Turn ignition switch to "OFF" position. Start engine and drive vehicle straight forward at a speed greater than 6 MPH (10 KPH). If pattern is not normal, compare to 626 & MX-6 DIAGNOSTIC CHARTS. (Scheme 8)
Note. On vehicles equipped with Anti-Lock Braking System (ABS). The ABS warning light may come on during these tests. This does not indicate a fault, and the light should go out when the ignition switch is cycled off at the end of testing.
Scheme 8
To test power to the control unit, disconnect the control unit connector. Turn ignition on. Check for battery voltage between terminals "O" (B+) and "Q" (ground). If voltage is not present check fuse and wiring circuits. To access the self diagnostic codes, connect a voltmeter between the terminal "G" (Check Terminal) of the control unit and ground. Turn ignition on. Record fault codes and compare to RX7 DIAGNOSTIC CHART.
Scheme 9
Scheme 10
To access the self diagnostic codes, connect a voltmeter between the test connector and ground. The diagnostic codes are displayed as voltage output pulses. Start the engine. Drive vehicle straight ahead at a speed greater than 6 MPH (10 KPH). Record diagnostic codes and compare to 929 DIAGNOSTIC CHART.
