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Home >> Buick >> 2003 >> Century Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics - 3.1L Engine >> Diagnostic Tests >> DTC P0420: Catalyst System - Low Efficiency >> Test Description

Test Description

The numbers below refer to the step numbers in the diagnostic procedure.

  1. 1  - The Diagnostic System Check-Engine Controls prompts the technician to complete some basic tests and store the Freeze Frame/Failure Records data on the scan tool, if applicable.
  2. 2  - If any component DTCs are set, diagnose those DTCs first. A fault in a component can cause the converter to appear degraded or may have caused the failure.
  3. 3  - Clearing the DTCs allows the catalyst test to be tested up to 18 times and completed up to 6 times this ignition cycle. If the A/C is not turned OFF the diagnostic may not run. The engine must be warm. Warm the converter by raising the engine speed above idle for the specified time prior to each attempted test. Has the DTC passed or failed this ignition cycle? If the DTC does not pass or fail look for a possible reason that would cause the test to abort.
  4. 4  - This step includes tests for conditions that can cause the 3-way converter to appear degraded. Repair any conditions before proceeding with this test.
  5. 9  - If the 3-way converter needs to be replaced, ensure that another condition which could damage the converter is not present. These conditions may include misfire, leaking or plugged fuel injectors, high engine oil or coolant consumption, retarded spark timing, or weak spark. Correct any possible causes of converter damage before replacing the converter.

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