P0420 Catalyst System Efficiency Below Threshold

[ec5780]

Hello

 

I have an 2006 FR-V, 2L petrol which has recently had a replacement catalytic converter and lambda sensors fitted after the originals were stolen.

 

A couple of months after they were fitted, the yellow engine malfunction light has been coming on. I've taken it to my local mechanic who found the P0420 Catalyst System Efficiency Below Threshold fault code (alongside P2185 - although P0420 was listed first and I've had P2185 sporadically before). He's cleared it a few times but each time it comes back on within a week.

 

I believe that P2185 has been resolved with a new coolant temperature sensor at the bottom of the radiator (the connectors in the old one were corroded) but I'm still left with P0420.

 

What's the best thing to do from here?

 

The mechanic has said he'll charge quite a lot just to diagnose this one.

 

Thanks in advance

[Trevor]

Cat system efficiency below threshold is usually associated with a difference in reading between sensor 1 and sensor 2.
Sometimes the cat could be blocked/damaged and not allowing flow but if you have a new cat then this would not be the issue.

The other possible cause could be there is an airleak between the joints on the cat (new gaskets should have been fitted after the flanges were cleaned up).

You can block the end of the exhaust with a rag and with the engine running (outside in fresh air) if you hear a hissing from any part of the exhaust system then this will be the air leak causing it to draw unregulated air into the cat.

[ec5780]

Thanks @Trevor for your reply.

 

The cat is new but my mechanic thinks that it could have failed as it's not a manufacturer original and apparently you can be unlucky with the pattern ones. He suggested going to an MOT station to ask them check the emission levels.

 

The first thing he did was to tried blocking the exhaust and looking for leaks but didn't find any leaks.

[Trevor]

22 hours ago, ec5780 said:

The cat is new but my mechanic thinks that it could have failed as it's not a manufacturer original and apparently you can be unlucky with the pattern ones. He suggested going to an MOT station to ask them check the emission levels.

 

 

The emissions they need to check are via the pre-mot test emissions check....specifically looking for Oxygen levels which should be as near to zero as possible (anything higher is suggesting drawing oxygen post-catalytic converter which will cause the problem.
 

[ec5780]

Thanks for that added detail. I'd just assumed the same check that they do when they perform an MOT would suffice.

 

I'll definitely bear this in mind.

[ec5780]

I'm still trying to get to the bottom of this.

 

I've asked a few MOT stations who performed a regular emissions check. Typically it would fail the first test but then pass on the fast idle test. However they didn't seem to know anything about doing an oxygen check.

 

Can anyone recommend anywhere, reachable from North London, that could do this for a reasonable price please?

[ec5780]

Thought I'd post an update here. Besides the MOT-style emissions check (see previous post) I wasn't able to find anywhere else that was able to give a more detailed readout of the gas levels.

 

So after looking around for other avenues of investigation I decided to replace the catalytic converter. That did sort out the fault code and the yellow light which - to me, suggests the catalytic converter was at fault, but when I tried to return the catalytic converter they claimed that it wasn't eligible for warranty return because HC reading on the emissions test I supplied was too high which indicates over fuelling.

 

Does this make sense? If the vehicle was over-fuelling which somehow was the root cause of the problem, wouldn't it continue to do so and the fault code would come straight back with the new catalytic converter?

 

They're offering that I can have the catalytic converter back that I tried to return for warranty claim. If they're trying to fob me off to avoid having to refund - then I should stand my ground but if they are right then does that mean the previous catalytic converter was actually working fine and I could resell it / try to use it on another vehicle? (I know that it's type specific so it wouldn't fit any other models which restricts the potential resale market for it but let's just leave that aside for now).

[Trevor]

Not sure without seeing absolute read outs on the emissions

Needless to say, if the HCs were high then this is unburnt fuel particles which cause the cat to run hot and even burn out completely.
If this is the case with the old cat then it would not be fit for reuse but the same could happen to the replacement one.
This is why it is important to get a proper emissions check (CO, CO2, HC, O2, Lambda) and this will tell you exactly what the failure is

[ec5780]

Thanks for responding again, I appreciate it.

 

The actual report was in another thread I posted - you mentioned that the report indicates that O2 levels were too high although O2 wasn't mentioned directly on the report.

 

I am not sure where I could get a full 5-gas emissions test done, looks like MOT test reports only show three of those figures.

[Trevor]

Yes, thats the problem nowadays as most garages don't understand the concept of exhaust emissions.
It either passes the MOT set emissions or it doesn't

I have seen many garages dispose of perfectly good oxygen sensors because they failed (or couldn't be bothered to see the relevance) to notice an exhaust leak which draws air to the sensor which then overfuels and 'hey presto' there is your problem.

I have sometimes measure the oxygen level after fitting a new exhaust to see that there is no leaks present and the repair has been done properly, takes all of 2 to 3 minutes as the emissions machine is running all day on standby.

Sorry, rant over but motor vehicle fundamentals seem to have been completely forgotten over the past 10 to 20 years and replacement of perfectly good (and expensive) components seem to be the name of the game.

 

 

most MOT emissions analysers have a 'Pre-MOT Test' function in the background where you can run it to check 5 gas and Lambda readings prior to testing for the MOT but not many people would use it or know its there or even understand the readings and how they determine the actual faults

[ec5780]

Thanks @Trevorfor this detailed and highly informative response.

It seems like it's more of a question of finding a technician competent to do the assessment than finding the equipment.

 

Wish I'd have known that earlier - every mechanic/garage I asked just ran the standard MOT tests and as you say - had no idea about the existence of the 5-gas analyser function.

 

If anyone knows of a garage in North West London area who understands these things, please feel free to chime in with a recommendation. At this point though, I guess it's now mostly a 'lesson learnt' (though I accept the point about the potential risk to the new catalytic converter if there is an underlying engine fault that is still present). I do still have a decision to make with respect to the old catalytic converter and whether to try to push the supplier to accept it as a warranty return, or whether to accept it back and try to re-use (or resell) it somehow.