code P0420 fixed w/Oxygen Sensor O2 Sensor Extender

adrian22 · Post by **adrian22** » 11 Feb 2019, 14:12

s60 2006 120k miles has engine check light and code P0420 “Catalyst System Efficiency Below Threshold (Bank 1).
car runs well with good 28mile/gal on highway
Question : is this an oxygen sensor issue? or Catalyst?
I used the lacquer thinner 1 gal/10gal gas but it did not fix it
Do you know if an Oxygen Sensor Extender Spacer will fix it?

Post by **RickHaleParker** » 11 Feb 2019, 15:03

Just about anything that messes with the air/fuel ratio can trip a P0420.
A extender does not fix the problem, it hides the problem by fudging the data.

Air leakage in the exhaust system.
One or more damaged injectors.
Damaged catalytic converter.

Post by **abscate** » 12 Feb 2019, 04:15

Not relevant for FL but in high smog states like CA a mod like this will be an automatic fail

adrian22 · Post by **adrian22** » 12 Feb 2019, 07:57

to add to this problem I noticed that if I run 93 fuel instead 89 it will fix the problem for a few weeks but after that the engine light is coming back-There is a suspicion that in states that do not have a smog test the gasoline is inferior since it will not matter for emission test-so it is possible that Fl 93 gas is in fact similar with 89 in CA

EngineeringBloke · Post by **EngineeringBloke** » 12 Feb 2019, 10:53

Engine computer compares front O2 sensor output with the back O2 output. The ECM adjusts the fuel air mix so it cycles a little and allows the cat to burn the extra fuel. If the back O2 sensor output is not level and follows the front O2 readings, then the cat is not working properly and the code is thrown.

Not sure why the O2 spacer or the less volatile 93 fuel help here.

Post by **RickHaleParker** » 12 Feb 2019, 17:27

EngineeringBloke wrote: ↑12 Feb 2019, 10:53 Not sure why the O2 spacer or the less volatile 93 fuel help here.

O2 sensors are designed to operate in the exhaust stream. A O2 spacer move the O2 sensor out of the exhaust stream resulting in false data. Spacers do not fix the problem, they cover up the problem by creating lies. If an inspector chemically analyzes the exhaust gases, the car will still fail inspection.

A higher octane fuel will be less prone to pre detonation, which does effect the burning of the fuel. This changes the chemical composition of exhaust gases.

Post by **precopster** » 13 Feb 2019, 04:13

At 120k miles the accuracy of an O2 sensor according to Bosch, Denso and NTK are questionable if the hype on their websites are to be believed.

In my case at around 140K miles a new front Bosch O2 sensor sorted this fault on my 2001 V70T5 and improved mileage. I swapped out the MAF with a new one at the same time. No Catalyst efficiency codes since then. Now at about 155k miles...

loveMy850 · Post by **loveMy850** » 26 Sep 2020, 21:54

Sorry to interrupt but can anyone please help me .one of my pins on the O2 connect is broken and won't stay in. I'm at a loss as what to do. I own a 1994 Volvo 850. Thank you, any info will help.

Post by **SuperHerman** » 27 Sep 2020, 19:20

loveMy850 - post a picture. You may be able to replace the pin or just hard wire a bypass. Picture will help with the best solution.

As to the O2 sensor extender - I had a set on the shelf so I tried them out on my X5 while I waited for my replacement cats to arrive. It didn't work. When I put the new replacement cats in I stuck an inspection scope into the cat to see what they looked like - they were clogged. The restriction of air flow was serious enough to make even an extender ineffective. In theory the idea should work, but if the cats are clogged the theory fails.

Post by **abscate** » 28 Sep 2020, 04:47

Let’s put the lacquer thinner and acetone in the fuel tank to solve code problems in the dustbin or crap where it belongs. Hope you didn’t damage anything doing that. Horrible advice with an ABS fuel tank.