P0420
DTC P0420 Catalyst System Low Efficiency
Circuit Description
A three-way catalytic converter is used in order to control the exhaust emissions of Hydrocarbons (HC), Carbon Monoxide (CO) and Oxides of Nitrogen (NOx). The catalyst within the converter promotes a chemical reaction which oxidizes the HC and the CO that is present in the exhaust gas. This will convert the HC and the CO into a harmless water vapor and a carbon dioxide, and reduces the NOx, converting the NOx into nitrogen. The catalytic converter also has the ability to store oxygen. The PCM has the capability to monitor this process by using a Heated Oxygen Sensor (HO2S) which is 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 the exhaust emissions effectively. The PCM monitors the catalyst efficiency by first allowing the catalyst to heat up, waiting for a stabilization period white the engine is idling Then, the PCM adds and removes the 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 illuminate.
Conditions for Running the DTC
- No active MAP DTC's
- No active IAT DTC's
- No active ECT DTC's
- No active TP DTC's
- No active Oxygen Sensor DTC's
- No active Fuel Trim DTC's
- No active Injector Control DTC's
- No active Misfire DTC's
- No active EVAP DTC's
- No active VSS DTC's
- No active IAC DTC's
- No active System Voltage DTC's
- No active PCM Memory DTC's
- No active CKP Variation Learn DTC's
- The engine has been running longer than 510 seconds.
- The BARO is above 72 kPa.
- The vehicle is in a Closed Loop operation.
- The vehicle has been driven above 1200 RPM for more than 36 seconds.
- Battery voltage is more than 9 volts.
Then, with the vehicle stopped:
- Engine is idling less than 150 RPM from the desired idle.
- The vehicle is in drive (automatic) or neutral (manual).
- The Throttle Position (TP) is 0 percent.
- The Engine Coolant Temperature (ECT) is between 75° C (167° F) and 125° C (257° F).
- The Intake Air Temperature (IAT) is between -20° C (-4° F) and 60° C (140° F).
- The Short Term (ST) fuel trim is between 93 (-28 percent) and 163 (+28 percent).
- The catalytic temperature is above 510° C (950°F) for 2.2L or 345° C (653° F) for 2.2L. In order 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.
- The above conditions are present for up to 30 seconds.
Conditions for Setting the DTC
The HO2S 2 response is too quick.
Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The PCM will record the operating conditions at the time that the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information.
- A history DTC stores.
Conditions for Clearing the MIL/DTC
- The MIL will turn off after 3 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.
- A scan tool can clear the DTCs.
Diagnostic Aids
An intermittent DTC can also be the result of a defective reluctor wheel. Remove the crankshaft sensor and inspect the reluctor wheel through the crankshaft sensor mount hole. Check the porosity and the condition of the reluctor wheel.
Whenever the DTC is an intermittent, refer to Symptoms.
Perform the fuel Injector Balance Test.
Steps 1 - 5:
Steps 6 - 7:
Test Description
The numbers below refers to the step numbers on the Diagnostic Table.
1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.
2. If any component DTCs are set, diagnose those DTCs first. A malfunction in a component can cause the converter to appear degraded or may have caused the malfunction.
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 you need to replace the three-way catalytic converter, make sure that another condition is not present which would cause damage to the converter. Correct any possible causes of converter damage before replacing the catalytic converter in order to avoid damage to the replacement converter.
These conditions may include the following items:
- Engine misfire
- High engine oil or coolant consumption
- Retarded spark timing
- Weak spark
6. Clearing the DTCs allows the catalyst test to be run up to 6 times this ignition cycle. Once the ignition switch is cycled, the test will run only once. Driving the vehicle heats the catalyst to a test temperature. The engine speed must be above idle for a predetermined amount of time before the PCM will allow the catalyst test to run. Once at idle, the PCM will allow the system to stabilize and then test the catalyst in 2 stages.
7. If you have found no malfunctions at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.