Clear the P0420 check engine light without replacing your catalytic converter with CelClear, a stainless steel O2 sensor spacer that uses a precise filter to dilute the gas the downstream sensor reads.
It threads into the standard downstream O2 port, placing a small pocket of post-cat gas at the sensor tip so the ECU sees the expected signal. No catalytic converter removal or replacement is required.
Constructed from real 304 stainless steel, CelClear withstands temperatures from -40°C to 700°C and resists corrosion. It fits 99% of modern vehicles with a standard M18 x 1.5 downstream O2 sensor thread.
Compatibility: M18 x 1.5 universal threading covers a wide range of makes — Audi, BMW, Subaru, Honda, Toyota, Ford, VW, Land Rover, and more. If your car uses this thread size, CelClear installs without adapters or thread tape.
| CelClear | Spark Plug Non-Fouler | New Catalytic Converter |
|---|---|---|
| M18*1.5 thread — fits 99% of vehicles | ❌ 18mm spark plug thread, wrong size for most modern cars | ❌ Replaces a part that's still working fine |
| Filter insert dilutes sensor reading properly | ❌ Hollow tube, often doesn't clear the code | ✅ Works, but $800–$2,000 installed |
| 304 stainless rated to 700°C | ❌ Zinc or aluminum, can melt or strip | ✅ OEM-grade material |
| Install in 5 minutes, one wrench | ❌ Quick install but unreliable on newer cars | ❌ Hours of labor + shop fees |
Three-step install — One wrench, five minutes:
Step 1: With the exhaust warm, unscrew the downstream O2 sensor using a 22mm wrench. Step 2: Thread CelClear directly into the empty O2 bung, starting by hand and then snugging with the wrench. Step 3: Reinstall the O2 sensor, start the engine, and drive 50–80 miles to clear the code.
What’s included: 1x CelClear adapter body, 1x filter element.
Questions you may have: Will this fit my car? If your downstream O2 sensor uses M18 x 1.5, roughly 99% of post-2000 vehicles qualify. Spark plug non-foulers with 18 mm threads will not fit; CelClear uses the correct M18 x 1.5. Is the material truly stainless steel? Yes, 304 stainless with a -40°C to 700°C rating and strong corrosion resistance. Will the light come back after driving? In most cases, once the code clears, the light stays off after 50–80 miles of normal driving; if the underlying issue is other than O2 readings, it may require separate attention. If it doesn’t work for your car, please revisit your sensor threads and installation steps, as alternatives may be needed for specific configurations.