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.
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
| Terminal/Description | Voltage | Condition |
|---|---|---|
| A/Ignition Signal | 12V | Ignition Switch "ON" |
| B/Battery Power | 12V | Ignition Switch "ON" |
| C/Air Conditioner Signal | 12V | A/C "ON" (all engine speeds) |
| D/Slow Fuel Cut Solenoid | 12V | 2500 RPM, terminals M and O disconnected |
| E, I, N | N/A | Not Necessary to Check |
| F/Air/Fuel Solenoid | O-12V | At idle speed |
| H/Throttle Positioner Solenoid | 12V | At 1700 RPM |
| K/EGR Solenoid | 12V | At 2500 RPM |
| M/ACV Solenoid | 12V | At idle speed |
| N, P, R/Ground | 0V | Ignition Switch "ON" |
| A/O2 Sensor | 0-1V | At idle speed |
| B/O2 Sensor (Sealed) | 0V | Ignition Switch "ON" |
| C/Water Temperature Sensor | 1.2V | At idle speed |
| D/Ground (Water Temp. Sensor) | 0V | Ignition Switch "ON" |
| I/Power Steering Signal | 12V | Power steering "OFF" |
| K, L/Vacuum Switch | 10V | Ignition Switch "ON" |
| M/Neutral & Clutch Switch | 0V | At idle speed |
| O/Idle Switch | 10V | At idle speed |
| Q/Water Thermo Switch | 0V | At idle speed |