c_benz300

I tried Rislone Cat Cleaner, STP 1 Tank Tuneup and Lucas Fuel System Cleaner and removed the code with my scan tool but the code came back right away after driving 50km.
The car sounds way better and is performing very well compared to before.
Broken oxygen sensor or the cat done?

JettaRed

iTrader: (1)

You can always try something like this to try to identify which part is faulty. Use it with your post-cat sensor. If the CEL goes away, it may be your cat. Or, you could replace the O2 sensor and see if that works.

TimC300

I have seen someone use

CRC Guaranteed to Pass Emissions Test Formula

and it supposedly cleared the check engine light.

Or replace the O2 sensor.

Just204

if the code says low catalytic converter efficiency or along that line 95% of the time it’s a bad catalytic converter. You’ll need a new one. It’s not the O2 sensor.

JettaRed

iTrader: (1)

So, how does the ecu determine the cat has low efficiency?

JettaRed

iTrader: (1)

https://www.carparts.com/blog/p0420-...rter%20Last%3F

Just204

the car can tell by how the oxygen sensor behind the cat reads. If it’s outside parameters it will trigger a code.

JettaRed

iTrader: (1)

Correct. It relies on the O2 sensor downstream of the cat. If the sensor is bad, it could cause the cat to appear low efficiency.

RobertR728

I replaced o2 sensors for my cat and it made zero difference. Replaced my cat with one from this company and it showed up in less than a week. Check engine light gone.

https://mufflerexpress.com/products/...6-bank-1-right

Just204

[QUOTE=RobertR728;8964143]I replaced o2 sensors for my cat and it made zero difference. Replaced my cat with one from this company and it showed up in less than a week. Check engine light gone.

https://mufflerexpress.com/products/...6-bank-1-right[/QUOTE

good to hear

c_benz300

After running a few more additives including another Rislone Cat Cleaner the code is still throwing p0420 bank 1 and bank 2 sensor reading too lean because of cat converter. Going to replace the cat shortly.

JettaRed

iTrader: (1)

See post #2.

TimC300

Check for exhaust leaks at the manifold?