Pcm Code P042 - Front Oxygen Sensor Lean Signal: Action

PCM turns on SERVICE ENGINE SOON light. PCM turns on canister purge solenoid if Code P044 is also set.

NOTE: Test numbers refer to numbers on diagnostic chart.

If PCM Code P017 is present, diagnose this code first since an oxygen sensor not ready can cause other emission related problems.
If oxygen sensor is operating correctly, voltage should fluctuate at greater than 0.3 volt. A lean sensor condition will cause voltage to remain at less than 0.3 volt.
If voltage measured is greater than 0.15 volt, PCM and circuit No. 1589 are okay. See POWERTRAIN CHARTS for reference to CHART 8.

Fig 1: PCM Code P042 Schematic - Front O2 Sensor Lean Signal

Courtesy of GENERAL MOTORS CORP.

Fig 2: PCM Code P042 Flow Chart - Front O2 Sensor Lean Signal

Courtesy of GENERAL MOTORS CORP.