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 MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROL SYSTEM - SELF-DIAGNOSTICS - 4.2LDIAGNOSTIC TESTSDTC P0420: CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)CONDITIONS FOR RUNNING DTC
2003 Chevrolet TrailBlazer 4.2 S, 4WD
Conditions For Running DTC
2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Conditions For Running DTC
- DTCs P0013, P0014, P0105, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0301-P0306, P0326, P0327, P0332, P0336, P0340, P0341, P0440, P0442, P0446, P0452, P0453, P0502, P0503, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1133, P1220, P1221, P1271, P1275, P1280, P1441, P1512, P1514, P1515, P1516, P1635, or P1639 not set.
- Engine speed is more than 1000 RPM for a minimum of 36 seconds since the end of the last idle period.
- Barometric (BARO) pressure is more than 21.3 in. Hg (72 kPa).
- Intake Air Temperature (IAT) is -5 to 176°F (-20.5 to 80.0°C).
- Engine Coolant Temperature (ECT) is 158-257°F (70-125°C).
- Battery voltage is more than 9 volts.
- The calculated air flow is less than 15 g/sec.
- Engine run time is more than 530 seconds.
- Vehicle speed is less than 3 MPH.
- Tests attempted this trip are less than 12.
- Predicted catalyst temperature is 934-1382°F (501-750°C).
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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.