Conditions for Running the DTC

WARNING: This page is about a different car, the 2006 Buick LaCrosse and 2006 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.

Before the ECM can report DTC P0420 failed, DTCs P0030, P0031, P0032, P0036, P0037, P0038, P0101, P0102, P0103, P0121, P0122, P0123, P0130, P0131, P0132, P0133, P0135, P0137, P0138, P0140, P0141, P0221, P0222, P0223, P0335, P0336, P0338, P167A, P2096, P2097, P2195, P2196, P2231, P2232, P2237, P2243, P2251, P2270, P2271, P2297 and P2626, must run and pass.
DTCs P0010, P0011, P0013, P0014, P0020, P0021, P0023, P0024, P0030, P0031, P0032, P0036, P0037, P0038, P0101, P0102, P0103, P0117, P0118, P0121, P0122, P0123, P0125, P0130, P0131, P0132, P0133, P0135, P0137, P0138, P0140, P0141, P0221, P0222, P0223, P0300, P0443, P0458, P0459, P0496, P2088, P2089, P2090, P2091, P2092, P2093, P2094, P2095, P2096, P2097, P2100, P2101, P2107, P2119, P2122, P2123, P2127, P2128, P2138, P2176, P2177, P2178, P2187, P2188, P2195, P2196, P2232, P2237, P2243, P2251, P2270, P2271, P2297 and P2626, are not set.
The air flow into the engine is between 10-42 g/s and not changing more than 8 g/s
The engine coolant temperature (ECT) at engine start-up is more than -9°C (-16°F).
The engine is operating for more than 320 seconds.
The engine is operating in Closed Loop.
The calculated TWC temperature is between 465°C (869°F) and 630°C (1,166°F) and steady.
DTC P0420 runs once per ignition cycle when the above conditions exist for approximately 17 minutes. The ECM will restart the test up to 4 times per ignition cycle, if the conditions above are interrupted during the test.