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Home >> GMC >> 1989 >> Forward Control 7.4 W, Standard >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> CCC TBI Tests W/Codes >> Diagnostic Charts >> Code 13 - Oxygen (O2) Sensor Circuit >> Test Description
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Test Description

NOTE: Test numbers refer to test numbers on diagnostic chart.
  1. Code 13 will set under the following conditions:
    • Engine at normal operating temperature.
    • At least 2 minutes of operation after engine starts.
    • Oxygen sensor voltage signal steady between .35 and .55 volt.
    • Throttle position sensor signal above 4%.
    • All of these conditions must be sustained for about one minute. If conditions for Code 13 exist, system will not go into "Closed Loop" mode of operation.
  2. This determines if sensor is at fault, or if wiring or ECM is cause of Code 13.
  3. Use only a high impedance digital volt/ohmmeter. Test checks continuity of circuit No. 412 and circuit No. 413. If circuit No. 413 is open, ECM voltage on circuit No. 412 will be over .6 volt (600 millivolts).
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