Circuit/System Description
In order to maintain a reasonably low emission level of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) a 3-way catalytic converter (TWC) is used. The catalyst within the converter promotes a chemical reaction that oxidizes the HC and CO present in the exhaust gas. This reaction converts the gases into harmless water vapor and carbon dioxide. The catalyst also reduces the NOx , converting the NOx into nitrogen. The engine control module (ECM) monitors this process using the post catalyst heated oxygen sensor (HO2S) signal. The post-catalyst HO2S located in the exhaust stream after the TWC, produces an output signal that indicates the oxygen storage capacity of the catalyst. The oxygen storage capacity (OSC) determines the ability of the catalyst to convert the exhaust emissions effectively. If the catalyst is functioning correctly, the post-catalyst HO2S signal will be far less active than the signal produced by the pre-catalyst HO2S.
To determine OSC, the ECM commands a rich air/fuel mixture until all oxygen is removed from the catalyst. The ECM then commands a lean air/fuel mixture and monitors the rear heated oxygen sensors to calculate the oxygen storage capacity. The catalyst is operated in this mode until one of the following conditions occur:
•The oxygen stored in the catalyst exceeds a calibrated threshold, which is determined from the rear HO2S signal.
•The rear HO2S indicates the catalyst to be completely saturated with oxygen, which is determined from the rear HO2S signal.
Conditions for Running the DTC
•Before the ECM can report DTCâ€P0420 or P0430 failed, DTCsâ€P0030, P0031, P0032, P0036, P0037, P0038, P0050, P0051, P0052, P0056, P0057, P0058, P0100, P0101, P0102, P0103, P0121, P0122, P0123, P0131, P0132, P0133, P0135, P0137, P0138, P0140, P0141, P0151, P0152, P0153, P0155, P0157, P0158, P0160, P0161, P0221, P0222, P0223, P0335, P0336, P0338, P2096, P2097, P2098, P2099, P2195, P2196, P2197, P2198, P2232, P2235, P2237, P2240, P2243, P2247, P2251, P2254, P2270, P2271, P2272, P2273, P2297, P2298, P2626, and P2629 must run and pass.
•DTCâ€P0010, P0011, P0013, P0014, P0020, P0021, P0023, P0024, P0030, P0031, P0032, P0050, P0051, P0052, P0100, P0101, P0102, P0103, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0128, P013A, P013C, P013E, P0130, P0131, P0132, P0133, P0135, P0137, P0138, P014A P0140, P0141, P0150, P0151, P0152, P0153, P0155, P0157, P0158, P0160, P0161, P0221, P0222, P0223, P0300, P0301-P0306, P0443, P0455, P0458, P0459, P0496, P0497, P2088, P2089, P2090, P2091, P2092, P2093, P2094, P2095, P2096, P2097, P2098, P2099, P2100, P2101, P2107, P2119, P2122, P2123, P2127, P2128, P2138, P2176, P2177, P2178, P2179, P2180, P2187, P2188, P2189, P2190, P2232, P2235, P2270, P2271, P2272, or P2273 is not set.
•The engine speed is 1,160-2,440â€RPM.
•The engine load is 13-80â€percent.
•The air flow into the engine is between 3-28â€g/s and steady.
•The ambient air temperature is warmer than −30°C (−22°F).
•The HO2Sâ€2 is at operating temperature for greater than a range of 140-210â€seconds.
•The Closed Loop fuel control is enabled.
•The calculated TWC temperature is between 500-900°C (932-1,652°F) and steady.
•The above conditions exist for approximately 17â€minutes.
•DTCs†P0420 and P0430 run once a drive cycle. The ECM will attempt to run this diagnostic up to 3â€times per drive cycle.
Conditions for Setting the DTC
The ECM determines the oxygen storage capacity (OSC) of the catalyst has degraded below a calibrated threshold. The DTC sets when the condition exists during the sample period, then a 5â€second delay for the MIL.
Action Taken When the DTC Sets
DTCsâ€P0420 and P0430 are Typeâ€A DTCs.
Conditions for Clearing the DTC
DTCsâ€P0420 and P0430 are Typeâ€A DTCs.
Diagnostic Aids
Inspect for the following conditions, which may cause a catalytic converter to degrade:
•An engine misfire
•High engine oil or high coolant consumption
•Retarded spark timing
•A weak or poor spark
•A lean fuel mixture
•A rich fuel mixture
•A damaged oxygen sensor or wiring harness