LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> GMC >> 1995 >> Forward Control 7.4 N >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests - 7.4L >> Engine Sensors & Switches >> Oxygen Sensor (O2S)
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Oxygen Sensor (O2S)

  1. Start engine and warm to operating temperature. Disconnect oxygen sensor. Connect DVOM between Purple lead of oxygen sensor and ground. Place DVOM on 2-volt scale.
  2. Using another DVOM on 20-volt scale, connect DVOM in series between Purple wire from ECM/PCM/VCM and positive post of battery. This will simulate a rich condition, causing ECM/PCM/VCM to respond by leaning mixture. Reading on DVOM connected to oxygen sensor should decrease to less than .3 volt.
  3. Move DVOM lead from positive battery post to negative battery post. This will simulate a lean condition, causing ECM/PCM/VCM to respond by richening mixture. Reading on DVOM connected to oxygen sensor should increase to greater than .8 volt. If reading does not change as specified, replace oxygen sensor.
  4. If a second DVOM is not available, connect a jumper in Purple wire from ECM/PCM/VCM. Hold jumper in one hand and touch positive post of battery with other hand to simulate a rich condition. Touch negative post of battery to simulate a lean condition. For additional testing procedures, see TESTS W/CODES - 7.4L article.
scientia non olet · About LEMON Manuals