GM OBD Trouble Code 42

Ignition Bypass Circuit Error

The ECM monitors the Ignition Bypass circuit and will set code 42 to signal an error. The ignition bypass circuit allows the ECM to switch the ignition module from "base" timing to computer-controlled timing advance.

Fault Code Description

  • 42 - Ignition bypass circuit error


  • Slight lack of power may be noted

Common Problems

  • Ignition control module
  • Wiring issue between the ignition module and the ECM

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Could you please tell me where the ignition module is located on a 1994 celica gt