Electronic Control Unit (Ecu)
- The ECU may be tested using a voltmeter. Engine must be at operating temperature. For testing, ignition switch must be in "ON" position and engine not running. Measure voltage at each terminal and compare values to ELECTRONIC CONTROL UNIT TESTING chart. See Fig 1 .
- The ECU has a built-in fail safe mechanism. If certain malfunctions occur during vehicle operation, the ECU will automatically initiate a command so driving performance will not be affected. See CONTROL UNIT MALFUNCTION STRATEGY table.
CONTROL UNIT MALFUNCTION STRATEGY
| Malfunction | Command Sent Out |
|---|---|
| Water thermo-sensor | Control unit outputs a constant 80°C (176°F) command. |
| Feed back system | Control unit holds A/F solenoid to duty 20%. (dwellmeter reading: 18°) |
| Vacuum Sensor | Control unit prevents operation of EGR valve, and holds A/F solenoid to duty 0%. |
| EGR position Sensor | Control unit prevents operation of EGR valve. |