Vacuum Piston Control Solenoid Valve
- Detach control box from its mounting and open control box lid. Disconnect lower vacuum hose of vacuum piston control solenoid valve from "T" fitting and connect a vacuum pump to lower port of solenoid valve. See Fig 1.
- Disconnect the No. 28 vacuum hose on solenoid valve from hose manifold and connect a vacuum gauge to hose. See Fig 1. Start engine and warm to normal operating temperature. Apply vacuum. Is vacuum present on gauge? If not, go to step 4). If so, quickly raise engine speed to 3000 RPM, then close throttle suddenly. Does vacuum reading on gauge decrease for a moment? If so, vacuum piston solenoid valve is okay. If vacuum does not react correctly, go to next step.
- Turn ignition off and disconnect the 8-pin connector on control box. Start engine and raise engine speed to 3000 RPM, then close throttle suddenly. Measure voltage between Yellow (pos.) wire terminal and Black (neg.) wire terminal on harness. Does battery voltage decrease for a moment? If not, replace solenoid valve. If voltage does decrease momentarily, check "CHECK ENGINE" warning light and self-diagnosis LED indicator. If okay, substitute a known good control unit and retest. If symptom goes away, replace original control unit.
- Turn ignition off and disconnect 8-pin connector on control box. Start engine. Measure voltage between Yellow (pos.) wire terminal and Black (neg.) wire terminal on harness. Is battery voltage present? If so, replace solenoid valve. If not, measure voltage between Yellow (pos.) wire terminal and ground. Is battery voltage present? If not, go to next step. If so, repair open in Black wire between control box and ground.
- If battery voltage was not present, check "CHECK ENGINE" warning light and self-diagnosis LED indicator. If okay, inspect for open in Yellow wire between control box and control unit terminal B14.
Courtesy of AMERICAN HONDA MOTOR CO., INC.