P0420
Diagnostic Chart:
Wiring Diagram:
Circuit Description
In order to control exhaust 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, convening them into harmless water vapor and carbon dioxide and reduces NOx, converting it into nitrogen. The catalytic converter also has the ability to store oxygen. The PCM has the capability to monitor this process using a Heated Oxygen Sensor (HO2S) located in the exhaust stream past the three - way catalytic converter. The HO2S produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalyst's ability to convert exhaust emissions effectively. The PCM monitors the catalyst efficiency by first allowing the catalyst to heat up, waiting for a stabilization period while the engine is idling and then adds and removes fuel while monitoring the reaction of the HO2S. When the catalyst is functioning properly, the HO2S 2 response to the extra fuel is slow compared to the O2S 1. When the HO2S 2 response is close to that of the O2S 1, the Oxygen storage capability or efficiency of the catalyst is considered to be bad and the MIL will be illuminated.
Conditions for Setting the DTC
^ DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0133, P0134, P0137, P0138, P0140, P0141, P0171, P0172, P0200, P0300-P0304, P0502, P0506, P0507, P0562, P0563, P0601, P1133, P1171 and P1441 not set.
^ Engine has been running longer than 510 seconds after the throttle has moved.
^ Barometric pressure (BARO) is above 72 kPa.
^ Vehicle is in Closed Loop.
^ Driven above 1200 RPM for greater than 180 seconds.
Then with the vehicle stopped:
^ Engine is idling less than 150 RPM from desired idle.
^ Vehicle is in drive (automatic) or neutral (manual).
^ Throttle Position (TP) is 0%.
^ Engine Coolant Temperature (ECT) is above 75°C (167°F).
^ Intake Air Temperature (IAT) is above -20°C (-4°F) and less than 80°C (176°F).
^ Short Term (ST) fuel trim is between 103 (-20%) and 153 (+20%).
^ Catalytic temperature is above 340°C (644°F). (To obtain the correct temperature to run the test, drive the vehicle until the converter temperature is 50°C (122°F) above the condition for running the DTC).
And
HO2S 2 response is too quick.
Action Taken When the DTC Sets
^ The Malfunction Indicator Lamp (MIL) will illuminate.
^ The PCM will record operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information.
^ A history DTC is stored
Conditions for Clearing the MIL/DTC
^ The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.
^ A history DTC will clear after 40 consecutive warm up cycles without a fault.
^ DTC(s) can be cleared by using the scan tool.
Diagnostic Aids
The catalyst test may abort due to a change in the engine load. Do not change the engine load (i.e. A/C, coolant fan, heater motor) while a catalyst test is in progress.
An Intermittent problem may be caused by a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation.
Any circuitry, that is suspected as causing the intermittent complaint, should be thoroughly checked for the following conditions:
^ Backed out terminals
^ Improper mating
^ Broken locks
^ Improperly formed or damaged terminals
^ Poor terminal to wiring connections or physical damage to the wiring harness
Refer to Intermittents. - Intermittent Malfunctions
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 and failure records 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 on the scan tool for later reference.
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 it's failure.
3. This step includes checks for conditions that can cause the three-way catalytic converter to appear degraded. Repair any problems found before proceeding with this table.
5. If the three-way catalytic converter needs to be replaced, make sure that another condition is not present which would caused the converter to become damaged. These conditions may include: misfire; high engine oil or coolant consumption; retarded spark timing or weak spark. To avoid damaging the replacement converter, correct any possible causes of converter damage before replacing the catalytic converter.
7. If no faults have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.
6. Clearing DTCs allows the catalyst test to be run up to 6 times this ignition cycle. Once the ignition is cycled, the test will run only once. Driving the vehicle heats the catalyst to a test temperature. The PCM must see predetermined amount of time at above idle before allowing the catalyst test to run at Idle. Once at idle, the PCM will allow the system to stabilize and then test the catalyst in 2 stages.