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Home >> GMC >> 1991 >> Value Van 7.4 N >> Repair and Diagnosis >> External Pages >> Different car >> Section 41 (Engine Controls - Tests W/Codes - 5.9L Gasoline) >> Self-Diagnostic Tests >> Test TC-12A - O2S Stays Below Center (Lean) Or Left O2S Stays Below Center (Lean)

Test TC-12A - O2S Stays Below Center (Lean) Or Left O2S Stays Below Center (Lean)

WARNING: This page is about a different car, the 1995 Dodge Ram Wagon, 1995 Dodge Ram Van, 1995 Dodge Pickup, and 1995 Dodge Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: For circuit and connector terminal identification, see CONNECTOR IDENTIFICATION  . For wiring diagram, see WIRING DIAGRAMS  section at the end of this article.
NOTE: BR body (heavy duty engine) is equipped with dual O2S. Scan tool displays dual O2S as LT O2S and RT O2S. On dual O2S systems, scan tool will read LT O2S in following steps.
  1. Start engine. Allow engine to run until normal operating temperature is reached. On light duty engine, go to step 5). On BR body (heavy duty engine), go to next step.
  2. Using scan tool, set engine speed to 1500 RPM. Using scan tool, read LT O2S sensor voltage. If LT O2S voltage is not always less than 0.5 volt, condition required to set trouble code is not present at this time. Go to next step. If LT O2S voltage is always less than 0.5 volt, go to step 4).
  3. LEFT O2S STAYS BELOW CENTER (LEAN) trouble code sets if LT O2S output voltage stays at less than 0.5 volt without switching for 8 minutes. Possible causes are: major vacuum leak, low fuel pressure, other engine sensor calibration failures, ignition system failure, LT O2S failure or mechanical engine problem. Go to TEST NTC-1A.
  4. If RIGHT O2S STAYS BELOW CENTER (LEAN) trouble code is not also set, a possible cause could be a shorted injector control circuit or a restricted injector. Go to TEST NTC-1A. If RIGHT O2S STAYS BELOW CENTER (LEAN) trouble code is also set, a condition causing engine to run lean in all cylinders is indicated. Go to TEST NTC-1A.
  5. Using scan tool, set engine speed to 1500 RPM. Using scan tool, read O2S voltage. If O2S voltage is not always less than 0.5 volt, condition required to set trouble code is not present at this time. Go to next step. If O2S voltage is always less than 0.5 volt, a condition causing engine to run lean in all cylinders is indicated. Go to TEST NTC-1A.
  6. O2S STAYS BELOW CENTER (LEAN) trouble code sets if O2S output voltage stays at less than 0.5 volt without switching for 8 minutes. Possible causes are: major vacuum leak, low fuel pressure, other engine sensor calibration failures, ignition system failure, O2S failure or mechanical engine problem. Go to TEST NTC-1A.
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