P0420
DTC P0420 TWC System Low Efficiency Bank 1
Circuit Description
To Control emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), a three-way catalyst (TWC) is used. The catalyst 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 powertrain Control module (PCM) has the ability to monitor this process using the Bank 1 HO2S 1 and the Bank 1 HO2S 2 heated oxygen sensors. The Bank 1 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 Bank 1 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 Bank 1 HO2S 1 signal will be far more active than that produced by the Bank 1 HO2S 2 sensor. If the PCM detects a level of Bank 1 HO2S 2 activity that indicates the catalyst is no longer operating efficiently, DTC P0420 will be set.
Conditions for Setting the DTC
- No related DTCs.
- The engine is operating in "closed loop."
- Engine air load is below 99%.
- Engine coolant temperature is between 70 °C (158 °F) and 120 °C (248 °F).
- Mass air flow is between 2.5 g/second and 10 g/second.
- Engine speed is below 200 RPM.
- Catalyst temperature is above 35 °C (662 °F).
- The PCM determines that the catalyst's oxygen storage capacity is below the acceptable threshold.
- Intake Air temperature is between -10 °C (14 °F) and 70 °C (158 °F).
Action Taken When the DTC Sets
- The PCM will illuminate the malfunction indicator lamp (MIL) the first time the fault is detected.
- The PCM will store conditions which were present when the DTC was set as Freeze Frame and in the Failure Records data.
Conditions for Clearing the MIL/DTC
- The PCM will turn the MIL "OFF" on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
- A history DTC P0420 will clear after 40 consecutive warm-up cycles have occurred without a fault.
- DTC P0420 can be cleared by using the Tech 2 "Clear Info" function or by disconnecting the PCM battery feed.
Diagnostic Aids
Check for the following conditions:
- 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 the harness appears to be OK, observe the display on the Tech 2 while moving connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the fault.
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
The "TWC Monitor Test Counter" displayed on the Tech 2 may be used to monitor the progress of the TWC diagnostic. To complete the TWC diagnostic with a good catalyst, the counter must be allowed to increment to 49 samples and roll over to 0 at least twice. A failed catalyst will require three or more 50-sample tests to report a failure.
Steps 1 - 2:
Steps 3 - 5:
Steps 6 - 7:
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart:
7. Difficulty completing the DTC P0420 "Status This Ign.." test may be encountered in areas where test conditions cannot be maintained easily, especially in urban areas. To minimize the amount of driving required to complete the DTC P0420 "Status This Ign.." test, use the following procedure:
- Allow the engine to warm completely.
- With the vehicle in "Park," monitor mass air flow on the Tech 2 and hold part throttle to maintain a reading of over 12 g/second for at least 2 minutes. This will achieve the "warm catalyst" required for running the test.
- Operate the vehicle in second or third gear to remain in the DTC P0420 test conditions described in "Conditions for Setting the DTC" as much as possible. If you must stop the vehicle, maintain the "warm catalyst" criteria as follows:
- Place the vehicle in "Park" or "Neutral."
- Hold part throttle to maintain a mass air flow reading of over 15 g/second for the duration of the stop.