Emission Control Systems: Testing and Inspection

1985-87 PRELUDE

If there is no voltage from control unit when there should be, or if there is voltage when there should not be, refer to following procedures. If no defects can be found, replace control unit and retest.

Inner Vent Solenoid Valve Circuit (Red/Green Wire)

1. Check for voltage at control unit connector with engine running. There should be voltage. If not, check regulator.
2. Check for voltage at control unit connector (black/yellow wire) with ignition switch on. There should be voltage. If not, check wiring.
3. Check black wire for continuity between control unit and suitable ground. There should be continuity.

Air Vent Cut-Off Solenoid Valve Circuit (Green/Yellow Wire)

1. Perform steps 1 to 3 for inner vent solenoid valve circuit.
2. Test thermosensor as follows. This thermosensor must be tested for resistance twice to confirm proper operation; once with engine in cold condition and then with engine in hot condition.
a. Ensure that engine is cold enough to perform first test by disconnecting hose No. 19 at charcoal canister. There must be no vacuum at idle.
b. Disconnect connector at control unit.
c. Check resistance between blue/yellow and white/black terminals. Resistance should be above 1k ohm.
d. Run engine until cooling fan comes on, then recheck resistance. Resistance should be about 200 ohms.
e. If resistance is not within specifications, replace thermosensor and repeat test.
f. If ohmmeter shows no continuity, check wiring and, if wiring is satisfactory, replace thermosensor and repeat test.
3. On 1985-86 models, test vacuum switch A as follows:
a. Disconnect No. 2 hose to control box at vacuum hose manifold, then connect suitable hand vacuum pump to the hose.
b. Check for continuity between black/yellow and brown/white wire terminals of control box connector.
c. Continuity should not be present when a vacuum of 3.9 inches Hg or more is applied. Continuity should be present when vacuum is released.