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 MANUALSCHEVROLET2001CHEVY EXPRESS G2500, VAN CARGO EXTENDED, 5.7 R, L31/KL8REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 45 (ENGINE CONTROL SYSTEM SELF-DIAGNOSTICS - 3.1L ENGINE)DIAGNOSTIC TESTSDTC P0420: TWC SYSTEM LOW EFFICIENCY (BANK 1)CONDITIONS FOR RUNNING DTC
2001 Chevrolet Chevy Express G2500, Van Cargo Extended, 5.7 R, L31/KL8
Conditions For Running DTC
2001 Chevrolet Chevy Express G2500, Van Cargo Extended, 5.7 R, L31/KL8SECTION Conditions For Running DTC
WARNING: This page is about a different car, the 2002 Pontiac Grand Prix, 2002 Chevrolet Malibu, and 2002 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
- Meet the conditions for engine warm up. Use the scan tool catalyst data list in order to verify the following conditions:
- DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0134, P0135, P0137, P0138, P0140, P0141, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0336, P0341, P0401, P0403, P0404, P0405, P0440, P0442, P0443, P0446, P0449, P0502, P0503, P0506, P0507, P1133, P1134, P1336, P1351, P1352, P1361, P1362, P1374, P1404, or P1441 are not set.
- The engine has been running for more than 10 minutes.
- ECT is 158-255°F (70-124°C).
- Barometric Pressure (BARO) is more than 75 kPa.
- Engine is in Closed Loop.
- Intake Air Temperature (IAT) is -4 to 212°F (-20 to 100°C).
- Battery voltage is more than 10.7 volts.
- Warm the catalyst:
- Fully open the hood.
- Place the transmission in Park (A/T) or Neutral (M/T).
- Set the park brake.
- PRESS and HOLD the service brake.
- Each time the engine is started the diagnostic can run up to 18 times. After the 10 minute run time, and before the diagnostic runs the first time, the engine must run an additional 5 minutes at 1500-2500 RPM. For any additional tests on the same key cycle, the engine must be at 1500-2500 RPM for 1 minute.
- In order to activate the diagnostic, return to idle and place the vehicle in Drive, or depress the clutch pedal for a manual transmission vehicle.
- Test the catalyst:
- Verify that the transaxle is in Drive (A/T) or is Neutral with the clutch pedal depressed (MT).
- Within 60 seconds, the air fuel ratio will go lean less than 14.1 for up to 7 seconds, and then may go rich, above 15.3 for up to 7 seconds.
- Use scan tool in order to determine if DTC P0420 has passed or failed this key cycle.
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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.