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[VXL V6]

Morning All

Just been on holiday for a week and the emissions lamp came on (lit all the time not flashing). Drove the car back to the caravan site and called the RAC (Asking them to just come out and read the codes), must have struck lucky with the RAC man as he was rather good with electronic diagnosis (on top of all of the standard RAC equipment he had his own oscilliscope, a tech 31 and various other code readers!).

The end diagnosis was 'Suspect CAT for Bank1&2, not performing to full potential, code P0420 (Bank1), code P0430 (Bank2) - CAT threshold'.

We could see the pre CAT sensor doing it's job succesfully - effectively reading and sending back a 'waveform' that you would expect, however the post CAT sensor was also mimicking this waveform as well which it shouldn't do as the output from the cat should need very little correction. From this he deduced that the CAT is not performing and recommended replacement.

Would people on here agree?

As i'm planning on keeping the car on for a while I was considering buying genuine new CATS (Do both sides?) from VX on TC, would anyone know the price?

Any thought's or comments most appreciated.

[VXL V6]

Bump

Anyone able to advise please?

Thanks

[jonathanh]

I've got no great expertise with CATs but I do think it is rather odd that both CATS, left and right bank fail at the same time.  Makes me think there is a common cause rather than simply CAT failure.  Got no clue what it could be but I'd try to ponder it a bit furthetr before I donated large chunks of money to Mr VX.


Hopefully someone more knowledgable that me can make a suggestion or two.  

[VXL V6]

Hi, Thanks for your reply.

I read it as Bank1&2 is the left hand (drivers side of the V) and Bank3&4 is the right hand side.

The diagnosis of the post sensor output is pretty conclusive IMHO of a failing CAT (I'm presuming that the system is effectively a closed loop for the CAT on each side so two circuits) because the post sensor is posting a waveform that suggests the CAT isn't doing it's job. If the sensor was duff I would guess it would just go high or low permanently.

[TheBoy]

Only 2 banks on GM V6.

If the cats have failed, for both to fail there has to be an external reason - ie the engine is throwing out something contaminating them...

[VXL V6]

Unburnt fuel maybe?

Don't know how I can prove what's going on then. Does PO420 and P0430 definately equate to both banks?

[VXL V6]

Thinking a little wider now.....

1) Forte Fuel System cleaner added a few tanks ago..... Car probably never had cleaner run through it before.....crap burn't off engine?
2) Journey down on holiday featured traffic jams, cat's must have got very hot.... should they not have cleaned themselves?
3) Would some of the CAT cleaner you can buy on eBay be worth running through? Opinions please.
4) I could go and get an emissions check and see what is coming out the back independently of the VX sensors... any point?

[JamesV6CDX]

There may be something much more simple to begin with.

Have you had a batch of cheap fuel whilst away?

Emissions, (CO and HC) would be interesting to know.

I can't see both cats failing at the same time, unless there is a serious engine problem.

Are the DTC codes that were stored present or historic?

[JamesV6CDX]

Hi, Thanks for your reply.

I read it as Bank1&2 is the left hand (drivers side of the V) and Bank3&4 is the right hand side.

The diagnosis of the post sensor output is pretty conclusive IMHO of a failing CAT (I'm presuming that the system is effectively a closed loop for the CAT on each side so two circuits) because the post sensor is posting a waveform that suggests the CAT isn't doing it's job. If the sensor was duff I would guess it would just go high or low permanently.

On right hand drive cars,

1-3-5 = drivers bank
2-4-6 = passenger bank

[Marks DTM Calib]

Has the light come on and stayed on?

Or is it just intermitent?

[VXL V6]

I believe the codes build up to a threshold which then triggers the emissions lamp - ie. it reaches a certain number of errors which can be over a period of time.

I only filled up once while away and that was after the codes had been cleared and the lamp had been extinguished. The car was filled up before going down from a local (busy) garage and drove down with no faults (say drove, more like crawled!).

When the lamp came on it was on a 15 mile trip after the car had been stood for a few days, the lamp came on and was solid, AFAIK it did not flash beforehand. The lamp hasn't lit or flashed since.

Shall I see if I can get an emissions test at my local garage so I can see what's coming out of it at the moment?

[VXL V6]

Right, had an emissions test at my local mechanics (He does my MOT's) and is a trustworthy chap. The car would pass an MOT emissions test with no problems. He checked the codes and they were logged again so he has cleared them. It will be interesting to see how many miles before the lamp is lit again.

Reading off his code reader / analyser, we could see all four sensors giving readings / switching so again it would seem to point to weak CAT's. His advise was that it wasn't worth changing anything yet, if it's passing the emissions well within the boundries then it's not like it's running terribly or anything.

The results at idle are:

CO 0.00%
HC 1ppm
CO2 13.40%
O2 0.27%
Lambda 1.01
NOx ---ppm

If that makes any sense to anyone.

[Marks DTM Calib]

Nothing wrong with those Cats......

No sign of hesitation, or miss fires?

[VXL V6]

Hi Mark

No, personally I think it feels fine, car pulls smoothly and easily, TBH it feels no different to normal.

Was thinking of getting the gearbox and climate software upgraded so was thinking of popping up to you when you have the time....  No pressure.

Perhaps you could give it your 'all knowing one' once over!!!

[Marks DTM Calib]

Any time you like....can easily do that little job for you.

We can also interogate the Engine software and see if there are any fixes released which might be relevant to the fault light.