Code .7.2 Throttle Switch Circuit

Fig. 21 Idle speed control throttle switch wiring circuit:

The ECM supplies a 12 volt signal to the idle speed control motor (ISC) pin B. When the engine operates at idle speed, the throttle linkage contacts the ISC plunger and closes the throttle (Idle) switch. This changes the voltage at ISC motor pin B harness terminal from 12 to zero volts. Code .7.2 indicates that the throttle switch is malfunctioning.
1. Turn ignition on and display Code .7.2. Manually depress and release ISC plunger.
2. If Code .7.2 is still displayed, proceed to step 3. If Code .7.2 passes, check for binding in throttle linkage and adjust as necessary.
3. Check idle switch and ISC plunger for binding in fully retracted position. If binding exists, proceed to step 4. If switch and plunger are satisfactory, proceed to step 5.
4. Disconnect ISC motor electrical connector, then extend plunger by grounding pin C and temporarily connecting pin D to 12 volts. Reconnect ISC motor and repeat switch test.
5. Disconnect ISC motor electrical connector with ignition on and Code .7.2 displayed.
6. Connect, then remove jumper wire between harness connector pins A and B. If Code .7.2 is still displayed, proceed to step 7. If Code .7.2 is no longer displayed, replace ISC motor.
7. Measure voltage at pin B of harness connector with ignition on. If voltmeter reads 12 volts, proceed to step 8. If less than 1 volt is recorded, proceed to step 9.
8. Check circuit 450 for an open. If circuit is satisfactory, fault is in ECM or ECM connector. Repair or replace as necessary.
9. Check circuit 427 for open or short. If circuit is satisfactory, fault is in ECM or ECM connector. Repair or replace as necessary.