By-Pass Control System
- Check by-pass valve shaft for binding, sticking and smooth movement. Ensure by-pass valve is in close contact with stopper when by-pass valve is fully open. Ensure by-pass valve is in close contact with full close screw when by-pass valve is fully closed. See Fig 1
.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
- Clean linkage and shafts with carburetor cleaner if fault is found. Start engine and allow to idle. Remove No. 2 vacuum hose from by-pass control diaphragm and attach a vacuum gauge to hose. See Figure
. Check for vacuum.
- If no vacuum is present in step 2), remove No. 12 vacuum hose from vacuum tank and check for vacuum at tank. If vacuum is present at tank, proceed to step 7). If no vacuum is present at tank, check vacuum line between tank and intake manifold. Repair as necessary and recheck.
- If vacuum is present in step 2), raise engine speed to 4000 RPM and check vacuum gauge. If vacuum is present, proceed to step 11). If no vacuum is present, connect No. 2 vacuum hose and disconnect No. 7 vacuum hose from by-pass control diaphragm. Attach vacuum gauge and check for vacuum at idle.
- If no vacuum is present, proceed to step 13). If vacuum is present, raise engine speed to 3500 RPM and check for vacuum. If no vacuum is present, system is okay. If vacuum is present, proceed to step 6).
- If vacuum is present at 3500 RPM, disconnect solenoid connector at firewall and check again for vacuum. See Fig 2
. If vacuum is now present, check Green wire between ECU terminal No. B3 and solenoid connector. If wire is okay, replace by-pass solenoid valve B. If no vacuum is present, replace ECU with known good one and check system again. Replace ECU if necessary.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
- If vacuum is present at tank in step 3), disconnect solenoid connector at firewall. Measure voltage between Black/Yellow terminal and Red/Blue terminal. If battery voltage is present, replace by-pass control solenoid valve A. If no voltage is present, proceed to step 8).
- If no battery voltage is present in step 7), measure voltage between Black/Yellow terminal and body ground. If no battery voltage is present, repair Black/Yellow wire between connector and fuse. If battery voltage is present, proceed to step 9).
- If battery voltage is present at step 8), turn ignition switch "OFF". Attach System Checker Harness (07999-PD6000A), between ECU and solenoid connector. Check for continuity between Red/Blue wire and ECU terminal A14. See Fig 2
.
- If no continuity is present, repair open in Red/Blue wire between ECU and connector. If continuity is present, connect a known good ECU and recheck. If voltage is now present, replace ECU.
- If vacuum is present in step 4), disconnect solenoid connector at firewall. If vacuum is now present, check Red/Blue wire. If wire is okay, replace by-pass control solenoid valve A. If no vacuum is present, proceed to step 12).
- If no vacuum is present in step 11), connect a known good ECU and recheck. If fault is not present, replace ECU.
- If no vacuum is present in step 5), disconnect solenoid connector at firewall. Check for battery voltage between Black/Yellow terminal and Green terminal. If battery voltage is present, replace by-pass control solenoid valve B. If no voltage is present, proceed to step 14).
- If no voltage is present, measure voltage between Black/Yellow terminal and body ground. If battery voltage is not present, repair open in Black/Yellow wire between connector and fuse. If battery voltage is present, proceed to step 15).
- If battery voltage is present, turn ignition switch "OFF". Connect System Checker Harness (07999-PD6000A), between ECU and connector. Check for continuity of Green terminal and ECU connector terminal B3. If no continuity is present, repair open in Green wire. If continuity is present, proceed to step 16).
- If continuity is present, connect a known good ECU and recheck. If voltage is present, replace ECU.