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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different car >> Section 92 (Engine Controls And Fuel - 2.8L (LWN) Diesel - Diagnostic Information And Procedures (1 Of 3)) >> Diagnostic Information and Procedures >> DTC P0421 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.
  1. Verify a condition does not exist with the component:
  2. Verify the following conditions do not exist:
    • If a condition exists 

      Repair or replace as necessary.

    • Go to next step: If no condition exists 
  3. Verify a condition does not exist with the component: Exhaust System & Oxidation Catalytic Converter
    • Cracked
    • Internal component rattle
    • Leaking - Refer to: Exhaust Leakage
    • Loose Clamps
    • Missing components
    • Restrictions - Refer to: Restricted Exhaust
    • Severe discoloration caused by excessive temperatures
    • Visible Damage
    • If a condition exists 

      Repair or replace as necessary.

    • Go to next step: If no condition exists 
  4. Retrieve the value from the time the DTC was set by using the Freeze Frame/Failure Records.
  5. Temperature sensor 1 must be at least 100°C (212°F) cooler than temperature sensor 2.
    • If within 100°C (212°F) of each other 

      Replace the component: Catalytic Converter

    • Go to next step: If not within 100°C (212°F) of each other 
  6. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

    Verify the DTC does not set.

    • If the DTC sets 

      Refer to step 1

    • Go to next step: If no DTC is set 
  7. All OK.