EGR Control Solenoid Valve

Disconnect vacuum hose at EGR valve. See Fig 1 . Connect vacuum gauge to hose. Warm engine until cooling fan comes on. Increase engine speed to about 3000 RPM. Check vacuum gauge. If vacuum is present, solenoid is okay.

Fig 1: Identifying EGR System
Courtesy of AMERICAN HONDA MOTOR CO., INC.
If vacuum is not present, disconnect connector from EGR control solenoid valve (at control box). Turn ignition on. Using voltmeter, check for voltage at EGR control solenoid connector. Connect voltmeter negative lead to ground, and backprobe connector's Black/Yellow wire terminal. If voltage is not present, check for blown fuse or open or short in EGR control solenoid power supply wire (Black/Yellow).
If voltage is present, increase engine speed to about 3000 RPM. Check voltage across solenoid terminals. If voltage exists but vacuum is not present, check for restricted hose or replace defective solenoid.
If voltage is not present, check for open in ground wire to solenoid. See appropriate WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section. If ground wire is okay, substitute a known good ECU, and retest. If problem goes away, replace original ECU.