Test 8 Vacuum Switches

NOTE: Observe the following instructions when performing the Subroutine Tests.


1. Do not measure voltage or resistance at the MCU module or connect any test light to it, unless otherwise instructed to do so.

2. Turn ignition key off and isolate both ends of a circuit whenever checking for shorts or continuity.

3. Connectors shown in schematics are viewed from front of connector.

4. Disconnect solenoids and switches from harness before checking continuity, resistance or by energizing by applying battery voltage directly.

5. Follow each step in order beginning with the first one in the appropriate routine. Follow each step until the problem is located, then correct the problem and perform the appropriate Functional Test to make sure that the problem has been corrected.

Fig.7 - MCU Vacuum Switch Location & Identification:

Test 8-Vacuum Switches, Fig. 7.

1. Make sure there is proper amount of vacuum at switch. For switches 1, 2, and 3, with engine at idle, gauge should show 8 inches Hg or more.

2. If vacuum does not meet required specification, check vacuum lines for any blockage or leakage. Also check ported vacuum switch, thermal vacuum switch, if suspect.

3. Measure resistance of vacuum switch contacts. Switch contacts should show continuity without vacuum. if resistance is less than 5 ohms, go on to next step. If resistance is more than 5 ohms, replace switch.

4. Check vacuum switch contacts with vacuum applied to switch. Measure resistance of contacts. If resistance is less than 5 ohms, go to next step. If resistance is more than 5 ohms, replace switch. Contacts should be open at 20 inches Hg or more.

5. Check circuit 60 for continuity. If resistance is less than 5 ohms, go to next step. If resistance is more than 5 ohms, service circuit 60.

6. Check circuit (+) for continuity. If resistance is less than 5 ohms, go to next step. If resistance is more than 5 ohms, service circuit (+).

7. Check circuit (+) for short to ground. If resistance is less than 1000 ohms, replace MCU module. If resistance is more than 1000 ohms, service short in circuit (+).