Test 3 Vacuum Switch Open

Fig.10 - Electrical Vacuum Switch Circuit:

High/Low Vacuum Switch (Code 51)
1. With ignition key off, disconnect vehicle harness from vacuum switch connector.

2. Check resistance of high/low vacuum switch circuit 75 to 60, Fig. 10. If resistance is 10 ohms or less proceed to next step. If resistance is greater than 10 ohms, replace switch.

3. Disconnect the 24-pin connector from MCU module and check circuits 60 and 75 using an ohmmeter, Fig. 10. If resistance is 10 ohms or less, replace MCU. If resistance is greater than 10 ohms, repair the circuit.

Midvac Switch (Code 55)
1. With engine at idle, disconnect vacuum switch hose and check for manifold vacuum from hose. If there is vacuum, proceed to next step. If there is no vacuum, check hose for leakage, obstructions or incorrect routing. Make necessary corrections and retest.

2. With ignition key off, disconnect vehicle harness from vacuum switch connector, then apply at least 15 inches Hg vacuum to switch.

3. Check resistance of vacuum switch circuit 213 to 60, Fig. 10. If resistance is 10 ohms or less, reconnect vacuum hose and proceed to next step. If resistance is greater than 10 ohms, replace switch assembly.

4. Disconnect 24 pin connector from MCU module and check circuits 60 and 213, Fig. 10 of the vehicle harness for continuity using an ohmmeter. If resistance is 10 ohms or less, replace MCU. If resistance is greater than 10 ohms, repair circuit.