Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1983 Mazda 626 Base, 4D HatchbackFACTORY OEM SERVICE PROCEDURE
Control Units
- The control unit may be tested with a voltmeter. Engine must be at operating temperature. For testing, ignition switch must be "ON" and engine not running. Measure voltage at each terminal and compare values to appropriate Control Unit Testing chart.
- The control unit has a built-in fail safe mechanism. If certain malfunctions occur during driving, the control unit will automatically initiate a command so driving performance will not be affected. See Control Unit Malfunction chart.
CONTROL UNIT MALFUNCTION CHART
| Malfunction | Control Unit Action |
|---|---|
| Water Thermo Sensor | Outputs a constant 176°F (80°C) command |
| Oxygen Sensor | Holds A/F solenoid to duty 20% |
| Vacuum Sensor | Prevents operation of EGR valve; holds A/F solenoid to duty 0% |
| EGR Position Sensor | Prevents operation of EGR valve |
CONTROL UNIT TESTING (1)
| Terminal/Description | Voltage | ||
|---|---|---|---|
| A/Ignition Coil Negative Terminal | 12V | ||
| B/Ignition Power Supply | 12V | ||
| C/Air Conditioner Relay | 12V with A/C "ON" | ||
| E/System Check Terminal | 12V; below 1.5V after .4 sec. | ||
| I/System Check Terminal | 12V; below 1.5V after 2 sec. | ||
| F/Air/Fuel Solenoid Valve | 12V | ||
| H/Coasting Richer Solenoid Valve | 12V | ||
| D/Slow-Fuel-Cut Sol. Valve | Below 1.5V | ||
| J/Air Conditioner Solenoid | 12V | ||
| K, L/Duty Solenoid Valve | 12V | ||
| M/Solenoid Valve for ACV | 12V | ||
| N, R/Ground | 0V | ||
| A, B/O2 Sensor | Below 1.5V | ||
| C/Water Thermo-Sensor | 3.4V at 68°F (20°C); 1.1V at 176°F (80°C) | ||
| D/Water Thermo-Sensor Ground | Below 1.5V | ||
| E/Vacuum Sensor | 4V | ||
| F/Vacuum Sensor Ground | Below 1.5V | ||
| G/Vacuum Sensor | 5V | ||
| H, J/EGR Position Sensor | Below 1.5V | ||
| L/EGR Position Sensor | 5V | ||
| K/Vacuum Switch | 12V | ||
| M/Clutch & Neutral Switch | 12V | ||
| N/Ignition Switch "Start" Terminal | Below 1.5V; 10V at "START" | ||
| O/Idle Switch | 12V | ||
| P/Idle & Vacuum Switch Ground | Below 1.5V | ||
| Q/Water Thermo Switch | Below 1.5V at 63°F (17°C) | ||
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Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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