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.