LEMON Manuals: Even more car manuals for everyone
Home >> Chevrolet >> 2001 >> Venture Base, Van Passenger >> Repair and Diagnosis >> External Pages >> Different car >> Section 213 (Engine Controls - Self-Diagnostics - 3.0L) >> Diagnostic Tests >> DTC P0421 Or P0431: Warm-Up Catalyst - Below Threshold >> Test Description

Test Description

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.

The number below refers to the step number on the diagnostic procedures.

  1. 6 -  This step includes inspections for conditions that can cause the TWC converter to appear degraded. Before you proceed with this test, repair any conditions that you find.


  1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS .
  2. Observe the DTC information on the scan tool. Are there any other component DTCs set? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  3. Allow the engine to reach operating temperature. Ensure closed-loop operation is achieved. Increase the engine speed to 1500 RPM for one minute. Return the engine to a stabilized idle. Monitor the HO2S 1 and HO2S 2 for the applicable bank. Is the HO2S 2 voltage parameter as active as the HO2S 1 voltage parameter for the applicable bank? If yes, go to step  5. If no, go to next step.
  4. Clear the DTCs with a scan tool. Start engine. Operate vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did DTC P0421 or P0431 set? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
    5. NOTE: Verify that the TWC converter is a high quality part that meets the OEM specifications.
  5. Visually and physically inspect the TWC converter for dents or damage, severe discoloration caused by excessive temperatures, holes or punctures, or internal rattles caused by a damaged catalyst element. Did you find a condition? If yes, go to step  9. If no, go to next step.
  6. Visually inspect the exhaust system for leaks, physical damage, loose or missing hardware, and HO2S 2 for proper torque. Did you find and correct the condition? If yes, go to step  10. If no, go to next step.
  7. Visually inspect the catalyst monitor HO2S 2 at the applicable bank for pigtail and wiring harness making contact with exhaust or any good ground, or for road damage. Did you find a condition? If yes, go to next step. If no, go to step  9.
  8. Replace applicable HO2S 2 sensor. After replacing sensor, go to step  10.
    9. NOTE: Locate and repair the cause of the TWC convertor failure before installing the replacement converter. See DIAGNOSTIC AIDS .
  9. Replace TWC converter. After replacing converter, go to next step.
  10. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step  2. If no, go to next step.
  11. Observe the Capture Info with a scan tool. Are there any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
scientia non olet · About LEMON Manuals