Hot Engine

1. Disconnect vacuum hose # 16 from the EGR valve and connect a vacuum gauge to the hose.
2. Attach the positive probe of the voltmeter to yellow/white terminal at control box # 1, and the negative probe to black terminal or ground.
3. Start engine and wait for engine to warm up; cooling fan must come on.

Fig. 65 Vacuum & Voltage Chart. Prelude W/Carbureted Engine:

Vacuum and voltage should be as shown:
1. Vacuum available for condition 1 or no vacuum available for conditions 2 & 3.
2. Verify vacuum hose routing. If there are no defects, replace the EGR control valves A and B (Box # 1).
3. No voltage for condition 1 or 4, or voltage available for conditions 2 or 3.
^ If there is no voltage, inspect Thermosensor, inspect vacuum switch C.
4. Check for voltage at control unit connector (black/yellow wire) with ignition switch on. There should be voltage.
^ If there is no voltage, check wiring.
5. Check brown/black wire for continuity between control unit and a suitable ground. It should have continuity.
6. Voltage and vacuum available for condition 4. Replace the EGR control solenoid valve A and re-test.