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DFI ECM Tests W/Codes: Action:

WARNING: This page is about a different car, the 1988 Cadillac Seville and 1988 Cadillac Eldorado. However, it is still accessible from the selected car via links, so may be relevant.

ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel.

The ECM controls engine idle by increasing or decreasing throttle opening using the Idle Speed Control (ISC) motor. The ISC will be active in controlling idle speed any time throttle switch is closed.

At vehicle speeds less than 6 MPH, the ECM controls idle speed based on engine RPM. When vehicle speed is greater than 6 MPH, the ECM controls idle speed based primarily on throttle opening (TPS) with adjustments to maintain a minimum engine RPM. Code EO30 is designed to detect engine RPM out of limits high or low.

NOTE: Test numbers refer to test numbers on diagnostic chart.
  1. This step checks for TPS misadjusted.
  2. This step checks for proper throttle switch, power steering switch, and park/neutral switch operation. The ECM must receive accurate switch status information in order to control idle.
  3. This step checks for proper ISC motor operation.
  4. Many engine fuel and emissions system faults may cause unstable idle. If base engine idle is not steady, ISC may not be able to control idle to within 150 RPM of desired idle.
  5. Minimum air rate, ISC, TPS, or ISC motor out of adjustment. Minimum air rate or TPS can cause ISC not to control idle, or code EO30 to set falsely.
  6. Checks ISC motor circuits for proper operation. Throttle switch input to ECM must be jumpered in order to allow ISC to cycle.
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