ECM Input E.7.2 - Throttle Switch Circuit: Notes
WARNING: This page is about a different car, the 1989 Cadillac Fleetwood and 1989 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
The throttle switch is part of the ISC. Terminal B of 4-way weatherpack connector on ISC is throttle switch or closed throttle input to ECM. The ISC throttle switch contacts are normally open and closed when throttle linkage contacts ISC plunger (closed throttle, ISC in control of idle speed).
The ECM sends a 5-volt signal to terminal B of ISC motor on circuit No. 427. When throttle linkage rests on ISC plunger, the throttle switch contacts close, shorting ISC terminal B to terminal A on circuit No. 450 (ground). The 5-volt signal from ECM is grounded at closed throttle, resulting in zero volts at ECM terminal C10. When throttle is opened, the throttle switch opens terminal B on circuit No. 427, resulting in 5 volts at ECM terminal C10.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- ISC plunger depressed and released should allow switch test to pass. If E.7.2 does not pass, check for ISC or circuit problems.
- When ISC motor is completely retracted, throttle switch will open due to ISC internal design. Ensure ISC is extended partially before continuing diagnosis.
- Checks for ISC or circuit problem. If E.7.2 passes, the problem is at ISC motor or connector.
- Checks for continuity on circuit No. 427 between ECM and ISC motor.