Lambda sensor cleaner: how to clear the P0420 error without replacing
The P0420 (Catalyst System Efficiency Below Threshold) error is one of the most common and expensive ECU errors. The most frequent cause is not the catalyst failure, but carbon deposits on the downstream lambda sensor. Before spending €600-1,500 for the replacement, try the chemical cleaner.
What the lambda sensor does
The lambda sensor measures the amount of oxygen in the exhaust gases and tells the ECU if the air/fuel mixture is correct. The one downstream of the catalyst verifies the correct operation of the catalyst itself.
Typical symptoms of a dirty lambda sensor
- Engine warning light (check engine) on
- Errors P0420, P0421, P0430, P0431
- Fuel consumption increase 10-15%
- Less responsive throttle
- Rough idle
- Emissions test failure
When the chemical cleaner works
The additive Blue Chem Lambda Sensor and Catalyst Cleaner works by dissolving the carbon deposits that cover the sensors and prevent correct reading. It works if:
- The catalyst is still physically intact
- The sensors are not mechanically broken
- The problem is from carbon buildup (most frequent cause)
Complete procedure
- With tank almost empty, pour the entire Blue Chem bottle into the tank
- Fill up completely
- Drive at least 50-100 km, including 30 km at sustained motorway speed (4,000-5,000 rpm)
- After treatment, clear the P0420 error with OBD-II
- Do a mixed driving cycle to check it doesn't reappear
When it does NOT work
- Catalyst melted or internally disintegrated
- Lambda sensor electrically faulty (resistance out of range)
- Exhaust leaks upstream of the catalyst
- Injectors impacting combustion (in that case also use injector cleaner)
Complete petrol engine treatment
For maximum effectiveness, combine the lambda sensor cleaner with Blue Chem Fuel System Cleaner (injector cleaning) and Blue Chem Valve Cleaner for the valves. Solves most P0420 problems without mechanical intervention.
Recommended products on LS Motors
- Blue Chem Lambda Sensor and Catalyst Cleaner – specific tank treatment
- Blue Chem Fuel System Cleaner – petrol injector cleaning
- Blue Chem Valve Cleaner – removes deposits on direct injection valves
Blue Chem additives Made in Germany, also used by official service centres. Shipping 24/48h throughout Italy.
