P0421

P0421 - WARM UP CATALYST LOW EFFICIENCY BANK 1
Catalytic converter efficiency is measured by how well the converter can store and release oxygen needed to convert CO, HC and NOx gases to C02 and water. Under normal operating conditions except heavy acceleration, cold engine temperatures and extended decelerations, the heated oxygen sensor (HO2S) bank 1 sensor 2 voltage should remain relatively steady between 500 mV and 800 mV. This steady reading of the HO2S bank 1 sensor 2 indicates a correctly functioning pre-catalytic converter as the air/fuel ratio changes slightly around 14.7 to 1. If the pre-converter is storing and releasing oxygen correctly. the HO2S bank 1 sensor 2 should hold its voltage value for a certain length of time as the air/fuel ratio increases or decreases. Under relatively steady cruise. the ECM will run a test which records the voltage amplitude values of the HO2S bank 1 sensor 2 as an oscillating air/fuel ratio is introduced. The ECM will then compare the amplitudes it obtained to modeled values of a new-failed catalyst. The closer the actual amplitudes of the HO2S bank 1 sensor 2 are to the modeled new-failed catalyst values. the more inefficient the pre-converter is becoming. DTC P0421 sets when the ECM has determined that the bank 1 pre-catalytic converter is no longer efficient.

DTC PARAMETERS
DTC P0421 will set if the ECM has determined the bank 1 pre-catalytic converter to be inefficient by using the HO2S bank 1 sensor 2 when:
^ Engine speed is between 1000 and 2120 rpm
^ Loop status bank 1 is closed
^ Engine load is between 20% and 45%
^ Calculated converter temperature is greater than 350°C (662°F)
^ No EVAP purge solenoid, EVAP flow during non-purge, fuel trim bank 1, HO2S bank 1 sensor 1, HO2S bank 1 sensor 2, MAF, misfire, TP sensor 1 or TP sensor 2 DTCs have been set.
^ DTC P0421 diagnostic is run once for 50 seconds once the above conditions have been met

P0421 is a type B DTC

DIAGNOSTIC AIDS
Make sure no exhaust leaks exist between the HO2S bank 1 sensor 1 and 18 in. after the HO2S bank 1 sensor 2. An exhaust leak in that area will cause false HO2S bank 1 sensor 2 readings and may set DTC P0421. Repair a leak if one exists and drive vehicle to verify the P0421 diagnostic has run and passed. Follow the enable conditions tinder DTC parameters.

A misfiring cylinder(s) on bank 1 pushing raw fuel out the exhaust port will damage the pre-converter over time. Verify that no current or history misfire counts exist in any failure record. Repair a currently misfiring cylinders if one exists.

Replace the bank 1 pre-catalytic converter.

NOTE: Bank 1 (cylinders 1, 3, 5) are closest to front of dash.