Diagnostic Aids

The scan tester cannot help diagnose Code 42 problems. If Code 42 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Fig 1: Code 42 Schematic - Electronic Spark Timing (EST) Circuit

Courtesy of GENERAL MOTORS CORP.

Fig 2: Code 42 Flow Chart - Electronic Spark Timing (EST) Circuit

Courtesy of GENERAL MOTORS CORP.