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Home >> Chevrolet >> 2001 >> Camaro Base, 2D Convertible, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 43 (Engine Control System Self-Diagnostics - 3.8L) >> Diagnostic Tests >> DTC P0420: TWC System - Low Efficiency >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Pontiac Firebird and 2002 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Are any other DTCs set? If yes, repair those DTCs first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
    3. NOTE: If the A/C is left ON the following diagnostic may not run.
  3. With a scan tool, refer to and record Failure Records and clear DTCs. Turn the A/C OFF. Fully open the hood. Operate the vehicle within the Failure Record conditions. If more than 6 tests have been attempted and the DTC has not passed or failed this key cycle the test may be aborting. See DIAGNOSTIC AIDS . The test may need to be completed up to 6 times in order to pass or fail. Does the scan tool indicate the DTC ran and passed this key cycle? If yes, system is okay. If no, go to next step.
  4. Visually and physically inspect the 3-way catalytic converter for damage. Inspect for the following:
    • Dents.
    • Severe discoloration caused by excessive temperatures.
    • Holes.
    • Internal rattle caused by damaged catalyst substrate.

    Also, ensure that the 3-way catalytic converter is a proper original equipment manufacturer part. Did you find damage? If yes, go to step  9. If no, go to next step.

  5. Visually and physically inspect the exhaust system for leaks. Did you find a condition? If yes, go to step  7. If no, go to next step.
  6. Visually inspect for the following:
    • Oxygen sensors for damage.
    • Oxygen sensors wiring harness for damage.

    Did you find a condition? If yes, go to step  8. If no, go to step  9.

  7. Repair the exhaust system as necessary. After repairs, go to step  10.
  8. Replace the oxygen sensor or repair the wiring as necessary. After repairs, go to step  10.
    9. NOTE: In order to avoid damaging the replacement 3-way catalytic converter, correct the engine misfire or mechanical fault before replacing the 3-way catalytic converter.
  9. Replace the 3-way catalytic converter. After repairs, go to next step.
    10. NOTE: If the A/C is left ON, the following diagnostic may not run.
  10. With a scan tool, clear the DTCs. Turn OFF the A/C. Fully open the hood. Operate the vehicle within the Failure Record conditions. If more than 6 tests have been attempted and the DTC has not passed or failed this key cycle the test may be aborting. See DIAGNOSTIC AIDS . The test may need to be completed up to 6 times in order to pass or fail. Does the scan tool indicate the DTC ran and passed this key cycle? If yes, go to next step. If no, go to step  4.
  11. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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