The 2022 Land Rover Range Rover Sport displaying a steady check engine light with P0420 indicates the catalytic converter on bank 1 isn't achieving expected efficiency levels. This emissions-related code requires careful diagnosis to distinguish between converter failure and upstream causes.
Understanding P0420
The engine control module compares upstream (pre-catalyst) and downstream (post-catalyst) oxygen sensor readings. A functioning catalyst significantly changes exhaust gas composition, creating different sensor readings. When readings become too similar, the ECM determines catalyst efficiency has declined below acceptable thresholds.
Bank 1 Identification
On the Range Rover Sport's V6 or V8 engines, bank 1 contains cylinder 1, typically the front-left cylinder bank. The associated catalytic converter processes exhaust from cylinders 1, 3, and 5 (V6) or 1, 3, 5, and 7 (V8).
Diagnostic Approach
Before condemning the catalytic converter, verify upstream conditions. Misfires, rich or lean operation, and exhaust leaks can cause P0420 without actual converter failure. Scan for additional codes that might indicate root causes. Check freeze frame data for conditions during code setting.
Oxygen Sensor Analysis
Monitor both upstream and downstream O2 sensors during steady-state cruising. The upstream sensor should oscillate actively between rich and lean. The downstream sensor should show minimal oscillation—a relatively steady voltage around 0.5-0.7 volts. If downstream sensor activity mirrors upstream sensor activity, the catalyst isn't converting effectively.
Exhaust Leak Inspection
Exhaust leaks between the engine and downstream O2 sensor can admit atmospheric oxygen, skewing sensor readings. Inspect manifold gaskets, pipe connections, and flex joints for leaks. A professional smoke test reveals leaks invisible to visual inspection.
Catalyst Condition Assessment
Temperature differential testing compares inlet and outlet catalyst temperatures. A functioning converter generates heat during the catalytic reaction—outlet temperature should exceed inlet by 50-100 degrees Fahrenheit. Similar temperatures suggest internal failure.
Repair Costs
If upstream issues caused the code, repairs vary based on root cause. Oxygen sensor replacement costs $200-400. Catalytic converter replacement on Range Rover Sport ranges $2,500-4,500 for OEM parts at dealers. Aftermarket converters may reduce costs but must meet emissions compliance.