42 Bypass Circuit - Open or Shorted

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The PCM/EC enables the EST mode by switching the bypass line high. When the bypass line is low the DIS module controls secondary coil firing. To enable EST the PCM/EC applies 5 volts on the bypass line (at approximately 400 RPM) indicating EST Mode to the DIS module. In EST mode the DIS module uses the EST signal from the PCM/EC to fire the secondary coils. The PCM/EC has internal feedback to monitor the state of the bypass line.

Code Parameters

Code 42 will set if:

  • The bypass line is open.
  • The bypass line is grounded.
  • The bypass line is shorted to voltage.

Diagnostic Aids

  • When attempting to diagnose an intermittent problem use the Scan Tool to review supplemental diagnostic information. The supplemental data can be used to duplicate a problem. Select MALF History from Scan Tool TC menu.
  • Check the tightness of the female terminal grip with a spare male terminal.
  • Refer to DIS in the Ignition section.

If using the SATURN PDT, at the end of the General Information table it will display a 42A, 42B, or 42C. See: Scan Tool Testing

  • 42A - Bypass line grounded.
  • 42B - Bypass line open.
  • 42C - Bypass line shorted to voltage.