Test 12 Thermactor Check (Code 44)

Fig.8 - MCU System Wiring Circuit:

1. Check for manifold vacuum at input to TAB-TAD solenoids. If manifold vacuum is present, proceed to next step. If there is no vacuum, correct vacuum routing and recheck.

2. Disconnect vacuum hose from TAB valve and connect a vacuum gauge to hose. Start engine and increase speed to 2000 rpm for 2 minutes. Shut off engine, then restart and initiate Self-Test while observing vacuum gauge. If vacuum pulses above and below 5 inches Hg vacuum, proceed to next step. If vacuum is always above 5 inches Hg vacuum, proceed to step 4. If vacuum is always below 5 inches Hg vacuum, proceed to step 7.

3. Reconnect hose to TAB and disconnect hose from TAD valve and connect a vacuum gauge to hose. Start engine and increase speed to more than 2000 rpm for 2 minutes. Shut off engine, then restart and initiate Self-Test while observing vacuum gauge. If vacuum pulses above and below 5 inches Hg, check Thermactor System. If vacuum is always above 5 inches, proceed to step 10. If vacuum is always below 5 inches Hg, proceed to step 12.

4. Check circuit 190 for short to ground by measuring resistance, Fig. 8. If resistance is greater than 1,000 ohms, proceed to step 6. If resistance is less than 1,000 ohms, repair short circuit.

5. Measure TAB solenoid resistance which should be 50-110 ohms. If resistance is within range, proceed to step 8. If resistance is not within range, replace solenoid.

6. Check output at TAB solenoid to make sure vacuum is not present when solenoid is de-energized (with vehicle harness disconnected and engine at idle). If there is vacuum, replace TAB solenoid. If there is no vacuum, replace MCU module.

7. Check vacuum hose between TAB valve and solenoid for leakage or blockage and correct as necessary. If okay, repeat step 5.

8. Check output at TAB solenoid to make sure vacuum is present when solenoid is energized. If vacuum is present, proceed to next step. If there is no vacuum, replace solenoid.

9. Check circuits 687 and 190 for continuity between the TAB solenoid and MCU module, Fig. 8. If resistance is greater than 5 ohms, repair the circuit. If resistance is less than 5 ohms, replace MCU module.

10. Check circuit 200 for a short to ground Fig. 8. If resistance is greater than 1,000 ohms, proceed to next step. If resistance is less than 1,000 ohms, repair short circuit.

11. Check output at the TAD solenoid to make sure vacuum is not present when solenoid is de-energized (vehicle harness disconnected and engine at idle). If vacuum is present, replace TAD solenoid. If there is no vacuum, replace MCU unit.

12. Check vacuum hoses between TAD valve and TAD solenoid for leakage or blockage. Make necessary corrections. If okay, proceed to step 13.

13. Check TAD solenoid resistance which should be 50-100 ohms. If resistance is within specified range, proceed to next step. If resistance is not within range specified, replace solenoid.

14. Check output at TAD solenoid to make sure vacuum is present when solenoid is energized. If vacuum is present, proceed to next step. If no vacuum is present, replace solenoid.

15. Check circuits 287 and 200 for continuity between TAD solenoid and MCU module, Fig. 8. If resistance is greater than 5 ohms, repair circuit. If resistance is less than 5 ohms, replace MCU module.