P0420
Three Way Catalyst (TWC) System Low Efficiency:
Circuit Description
To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), a three-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The PCM has the ability to monitor this process using the HO2S 1 and the HO2S 2 heated oxygen sensors. The HO2S 1 sensor produces an output signal which indicates the amount of oxygen present in the exhaust gas entering the three-way catalytic converter. The HO2S 2 sensor produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalyst's ability to convert exhaust gases efficiently. If the catalyst is operating efficiently, the HO2S 1 signal will be far more active than that produced by the HO2S 2 sensor. If the PCM detects a level of HO2S 2 activity that indicates the catalyst is no longer operating efficiently, DTC P0420 will be set.
Conditions for Running the DTC
^ Engine coolant temperature between 70°C (158°F) and 11O°C (230°F).
^ Intake air temperature between -10°C (14°F) and 50°C (122°F).
^ Barometric pressure greater than 75 kPa.
^ Fuel tank level greater than 25%.
- Engine Speed between 2300 and 4500 RPM.
^ Calculated load value between 26 and 80%.
^ In closed loop mode 360 seconds from engine start.
Conditions for Setting the DTC
^ Delay time average of HO2S 2 response.
^ Conditions present for 45 seconds.
Action Taken When the DTC Sets
^ The Malfunction Indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.
^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.
Conditions for Clearing the MIL/DTC
^ The MIL will turn "OFF" after three consecutively passing cycles without a fault present.
^ A History DTC will clear after 40 consecutive warm-up cycles without a fault.
^ DTC(s) can be cleared by using a scan tool or by disconnecting the PCM battery feed.
Diagnostic Aids
Check The Following Conditions:
^ Exhaust gas leaks.
^ Three way catalytic converter malfunction.
^ Fuel system malfunction.
^ HO2S sensor 1 and sensor 2 malfunctions. If a HO2S DTC is set, refer to the applicable DTC first.
^ Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
^ Damaged harness. Inspect the wiring harness for damage.
If DTC P0420 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
If any wiring repairs need to be made, Refer to Repair Procedures in Diagrams.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
2. Perform a visual/physical inspection of the catalytic converter.
6. A relatively inactive HO2S sensor 2 indicates that the converter is minimizing the amount of oxygen passing through the converter.