O2 sensor

[Mattyboy1]

My car kept coming up .
catalyst system bank 1 efficiency below threshold p0420.
So I changed the O2 sensor for one that I bought off someone who is a member on here who was breaking his car. And what a difference it made the car was pulling so much better and fuel economy went right up. I cleared the code when I fitted the sensor and its been ok for a week or so. Just went out to scan it just out of curiosity and its bought the code back up again. Car still seams to be pulling ok still though. I've deleted the code on again and will check in a few days to see if it comes back. But is there any reason why it would keep coming back I was told the sensor was only 6 months old.

 

[hyphon12]

Maybe your cat is on its way out? Which sensor did you replace though? as the post cat-lambda sensor doesn't effect fuelling.

 

[Mattyboy1]

It was the pre cat sensor . Car has a decat.

 

[hyphon12]

That's where you've went wrong as that fault is for the post cat sensor. Do you have a lambda spacer for the decat?

 

[Mattyboy1]

I thought bank 1 is the pre cat sensor. That's the one that does the fuelling mixture isn't it. I've got a spare post cat sensor and I've got a lambda spacer to go on it but it isn't fitted at the moment. What does the post cat sensor do.

 

[RICKY3]

Bank1 refers to first 4 cylinders only a v8 or so would have bank1 or bank2


Sent from my iPhone

 

[hyphon12]

Nah the code is generic so refers it to "Bank 1" as your engine only has the one bank. It's regarding engine banks on V and Boxer engines.

The spacer alone should cure the issue, its only there to monitor the cat i.e. checking it is doing its job, so with a decat it will be thinking its as the fault says "below efficiency".

But its not been a waste as your newer sensor has helped the car lol.

 

[RICKY3]

Both pre an post cat sensor codes have bank 1anyway


Sent from my iPhone

 

[LEE69]

Have a look through this http://www.obd-codes.com/p0420

 

[Mattyboy1]

Ok cheers for the replys. Will try and get the spacer fitted this weekend whist doing a few other jobs.

 

[W11TTX]

Bank one is pre cat and bank 2 is post cat iv had both of these issues on mine recently. Bank 1 was a knackerd pre cat sensor then I fitted a decat and got bank 2 system fault. Fitted a lambda spacer and its never been on since !

 

[CupraRmark]

Is your maf dieing ?? Does it need cleaning, covered in oil, the reason I ask is I recently had a friend who had same fault code and is maf was covered in oil causing the fault.......


Sent from my iPad using Tapatalk HD

 

[hyphon12]

Bank one is pre cat and bank 2 is post cat iv had both of these issues on mine recently. Bank 1 was a knackerd pre cat sensor then I fitted a decat and got bank 2 system fault. Fitted a lambda spacer and its never been on since !

Bank 1 isn't the pre-cat. It's just a generic fault so bank 1 or bank 2 can refer to either of them. It can't possibly flag up a precat sensor fault if its the "cat efficency" that's the problem.

 

[Mattyboy1]

Gonna try changing the post cat sensor in a little while and fit my spacer.

 

[W11TTX]

I'm confused then because when I rang my garage about the fault code and told them it said bank one they said its precat? Then when I Decatted I had the bank 2 on a fault code??


I wouldnt waste your money on a post cat lamba fit the spacer first and see it it cures it!

 

[BoostHard]

Its not the bank that referes to the sensor, The bank purely states which bank of cylinders has the fault,
Since these cars are straight 4 it will only ever be Bank1, is the s1 and s2 that tells you which sensor to look at,
S1 is pre cat S2 is post cat

 

[Mattyboy1]

I'm confused then because when I rang my garage about the fault code and told them it said bank one they said its precat? Then when I Decatted I had the bank 2 on a fault code??


I wouldnt waste your money on a post cat lamba fit the spacer first and see it it cures it!

Got a spare one knocking about so will see if i can change it.

 

[Mattyboy1]

Right so I've been and changed the rear sensor the battery was disconnected while I done it left it disconnected for over half hour. Connected the battery back up cleared all codes. Took the car for a blast and proper gave it some stick and it was absolutley flying. Came back scanned for codes and guess what.
Still got this

And got this one now aswell

So I pressume that the sensor I just put on is knackered
And I guess so is the front one aswell.

Can the front ones be cleaned.
It's still doing really good on fuel and going really well.

Also I've got to do a 40 mile round trip tomorrow will this do any damage driving it like this.

 

[BoostHard]

The bottom one is the rear lambda, post cat,

The top code........ try this


http://wiki.ross-tech.com/wiki/index.php/16804/P0420/001056



Also a link to a thread on there that may help

 

[hyphon12]

That other code is for the rear sensor as well. S2 = post cat sensor.

it won't do any damage as the rear sensor doesn't alter anything, the only thing it will do is put your engine light on.

But with that fault I've heard the MAF can cause it to come on. (Like what CupraRmark said).