Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1989STEP VAN P20, 4.8 T, AUTOMATIC, 400/M40REPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMCCC TBI TESTS W/CODESDIAGNOSTIC CHARTSCODE 13 - OXYGEN (O2) SENSOR CIRCUITTEST DESCRIPTION
1989 Chevrolet Step Van P20, 4.8 T, Automatic, 400/M40
Test Description
1989 Chevrolet Step Van P20, 4.8 T, Automatic, 400/M40SECTION Test Description
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- 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.
- This determines if sensor is at fault, or if wiring or ECM is cause of Code 13.
- 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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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.