Manual Transmission
DTC P0420 - TWC System Low Efficiency Bank 1 With Manual Transmission
Circuit Description
The PCM uses the Bank 1 HO2S 2 and the Bank 1 HO2S 3 heated oxygen sensors. The Bank 1 HO2S 2 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 3 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 2 signal will be far more active than that produced by the Bank 1 HO2S 3 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 above 60 °C (140 °F).
- Mass air flow is between 8 g/second and 50 g/second.
- Change in engine load is below 8%.
- Engine speed is below 3500 RPM.
- Vehicle speed is between 26 kph and 123 kph (16 mph and 75 mph).
- Catalyst temperature is above 399 °C (750 °F).
- The PCM determines that the catalyst's oxygen storage capacity is below the acceptable threshold.
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 scan tool 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 scan tool 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.
Steps 1 - 5:
Steps 6 - 7:
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart.
7. Difficulty in 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 scan tool 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.