This bulletin applies to 2016 Land Rover Discovery Sport vehicles and Range Rover Evoque vehicles involving potential degradation of the primary catalytic converter.
DTC P0420-00 stored in the PCM indicates that the primary catalyst is not operating at optimal level. The cause is fueling strategy when the engine is operated in overrun excessively and repeatedly during the warmup phase.
The DTC is monitored by the PCM, comparing O2 sensor readings from the front and mid oxygen sensors to determine the efficiency of the primary catalyst. While other components can impact the operation of the primary catalytic converter, the DTC P0420-00 will only be set based on the converter efficiency. Additional DTCs would likely be stored if other components are not operating as specified.
Diagnose and repair any related DTC(s), inspect for and repair any leaks in the exhaust system, inspect for and repair any intake system unmetered air leaks, inspect for and repair any causes of misfire in the ignition system, and carry out oil consumption checks.
If other components pass testing, do not replace. Replace only the primary catalytic converter. Ask the owner if the vehicle is often operated in an overrun during warm-up, such as driving downhill during warm-up as part of a daily routine.