Test 14 Thermactor Air Bypass Check (Code 46)

Procedure
1. Disconnect vacuum hose from TAB valve and connect a vacuum gauge to hose. Start engine and increase speed to above 2000 rpm for 2 minutes. Shut off engine then restart to initiate self test while observing vacuum gauge. If vacuum pulses above and below 5 inches Hg, MCU system is okay, check Thermactor output. If vacuum is always below 5 inches Hg, proceed to next step. If vacuum is always above 5 inches Hg, proceed to step 5.

2. Check vacuum hoses between TAB valve to TAB solenoid and between TAB solenoid and vacuum source for leaks or obstructions. If leaks or obstructions are found, service as required. If none are found, proceed to next step.

3. Check for vacuum at TAB solenoid when solenoid is energized. If there is vacuum, proceed to next step. If there is no vacuum, replace solenoid.

4. Check circuit 190 for continuity (resistance should be 10 ohms). If resistance is greater than 10 ohms, repair harness. If resistance is still greater than 10 ohms, replace MCU module.

5. Check that vacuum is not present at TAB solenoid output when solenoid is de-energized. If there is no vacuum, proceed to next step. If there is vacuum, replace solenoid.

6. Check circuit 190 for short to ground using an ohmmeter. If resistance is less than 1000 ohms, repair short. If resistance is greater than 1000 ohms, replace MCU module.