Code 4 - Vacuum Switch
- Engine is warm and running. Check engine warning light is on. and LED indicates a CODE 4. Turn the ignition sw. off. Remove EFI, ECU fuse in under-hood relay box for 10 seconds to reset control unit.
- Start engine and for at least 30 seconds let it idle. Check and see if CHECK ENGINE light is on and LED is indicating a CODE 4. If so then go to step 4 and if not then go to step 3.
- There is an intermittent failure. Check connectors at control box and control unit.
- Turn ignition switch off. Disconnect the 8P connnector on the control box. Measure resistance between terminals no. 5 and 6 on the control box. See Fig 1
. Does the continuity exist? If so then go to step 6 and if not go to step 5.
- Remove 7 hose, See Fig 2
, from the vacuum hose manifold and connect a T-Fitting from a vacuum gauge between the vacuum hose manifold and the vacuum sw. There should be more than 1.2" Hg of vacuum. If not replace vacuum sw. or repair open in BLK/YEL or WHT wire in the control box. If there is more than 1.2" Hg of vacuum, then check routing of 7 hose in Fig. Fig 2
.
- Turn ignition sw. ON. Measure voltage between BLK/YEL terminal and body ground on wire harness. There should be battery voltage. If there is go on to step 8. If not then go to step 7.
- Repair open in BLK/YEL wire between 8P connector and No. 12 fuse.
- Turn ignition sw. OFF. Reconnect 8P connector to control box. Connect ECU test harness A & B, See Fig 3
, between the control unit and connector. Turn the ignition sw. ON. Measure voltage between A10 (+) terminal and B8 (-) terminal, See Fig 3
. Is there battery voltage? If not go to step 9 and if there is go to step 10.
- Repair open in LT BLU wire between control unit (A10) and vacuum sw.
- Subsitute a known good control unit and recheck. If the symptom goes away, replace the original control unit.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Courtesy of AMERICAN HONDA MOTOR CO., INC.