Diagnostic Aids

The ECM supplies a 12-volt signal to the ISC motor pin B. When the engine is at idle speeds, the throttle linkage contacts the ISC plunger and closes the throttle switch whicl1 pulls the voltage on the ISC motor pin B to 0 volts.

Reconnect the ISC motor connector and rerun the switch tests.

1. Code .7.2 indicates that the throttle switch is malfunctioning. With the ignition on and Code .7.2 displayed, physically push the actuator plunger into its stop. If this results in Code .7.2 passing, check for mechanical binding in the throttle linkage such as throttle blades, shafts, throttle cable, Cruise Control linkage, TV cable, throttle position sensor, or throttle return springs. Also check the minimum air rate adjustment which may be holding the throttle open. The binding linkage is preventing the throttle switch from closing.
2. If Code .7.2 remains, check the ISC plunger and the idle switch for minding in the fully retracted position. IF the ISC plunger is binding, disconnect the ISC motor and extend the plunger by momentarily jumpering 12 volts to pin D of the ISC motor and jumpering pin C to ground. Reconnect the ISC motor connector and rerun the switch tests.
   NOTE: Only ISC pins C and D should have voltage applied to them. Jumpering ISC pins A and B will cause ISC motor damage. It may be desirable to make the jumper leads for this test from a 4-way weatherpack connector.
3. With ignition on and Code .7.2 displayed, disconnect the ISC motor and momentarily jumper harness pins A and B together. If Code .7.2 disappears, then replace the ISC motor.
4. If Code .7.2 remains, then the problem is in the wiring harness or the ECM. To identify the defective component, measure the voltage on harness pin B with the ignition on. If the voltage is 12 volts, then check circuit 450 for an open. If circuit 450 has continuity, then check for a faulty ECM connector or faulty ECM. If the voltage is less than 1 volt, then check circuit 427 for an open or short to ground. If circuit 427 is OK, check for a faulty ECM connector or faulty ECM because it is not providing the required 12 volt signal.