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HOMESERVICE MANUALSCHEVROLET2001CHEVY EXPRESS G3500, VAN PASSENGER EXTENDED, 6.5 FREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 155 (ENGINE CONTROLS - SELF-DIAGNOSTICS - 2.2L)DIAGNOSTIC TESTSDTC P0420: CATALYST SYSTEM EFFICIENCY BELOW THRESHOLDCONDITIONS FOR RUNNING DTC
2001 Chevrolet Chevy Express G3500, Van Passenger Extended, 6.5 F

Conditions For Running DTC

2001 Chevrolet Chevy Express G3500, Van Passenger Extended, 6.5 FSECTION Conditions For Running DTC
WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
  • DTCs P0068, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0171, P0172, P0201, P0202, P0203, P0204, P0220, P0300, P0326, P0327, P0336, P0340, P0341, P0442, P0446, P0452, P0453, P0496, P0500, P0506, P0507, P0601, P0602, P0603, P0604, P0606, P0641, P0651, P0700, P0701, P1133, P1134, P1137, P1138, P1516, P1680, P1681, P2120, P2125, P2135, P2138, or P2176 not set.
  • Engine has been running more than 9 minutes after the throttle has moved.
  • Vehicle is in a closed-loop operation.
  • Vehicle has been driven at greater than 1000 RPM for more than 35 seconds.
  • Air flow parameter is less than 8 g/s.
  • ECT is 158-257°F (70-125°C).
  • IAT is -6 to 176°F (-21 to 125°C).
  • Barometric pressure is greater than 21.3 in. Hg (72 kPa).
  • Ignition voltage is greater than 9 volts.
  • TWC calculated temperature is 1112-1247°F (600-675°C).
  • Vehicle speed is less than 3 MPH.
  • Engine must be at idle at less than 75 RPM or greater than 150 RPM of the desired speed.

This DTC is sampled once at an idle when the above conditions are met. If the first test fails, the ECM will take more samples during the current ignition cycle or may take samples for up to 6 ignition cycles. The extra sampling is to ensure that a converter has failed, not just temporarily poisoned.

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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.