The front cat on my 2011 mk3.5 2.0 PRHT Sport decided to evacuate itself, and has been replaced by an aftermarket unit from mx5parts.co.uk
The lower cat had to be replaced as well due to bits from the 1st one blocking it - there was basically no power, redline was effectively 5k rpm.
This is done, however the engine management light is still on, and the car is a very marginal emissions fail. The lower O2 sensor was “replaced” with a new part by the garage, however this made no difference to emissions and/or so the new sensor was put back in the box, and the old one replaced.
The EML is on due to 2nd O2 sensor reading lean.
The garage have advised me that the 1st cat is probably not doing the job (possibly EURO 4 spec vs EURO 5 which is what is needed, not sure about this). There is still a question mark over the upper O2 sensor, so they are not 100%
Is it worth replacing? I can get an aftermarket one but not sure about the correct part number. I believe the equivalent Denso patr is DOX-0560, but I see on eBay that other Denso sensors are being sold for the upper one e.g. DOX-0109.
According to denso-am.co.uk, the DOX-0560 is the direct fit regulating sensor for 2011 model, which I assume is the upper one, and the DOX-0109 is a universal fit diagnostic sensor, presumably the lower one.
Can anyone confirm this, and/or comment on the problem in general?
All the parts replacement and diagnostics are rapidly draining my bank account!
The breaking up of the front maniverter cat core will predictably block the second underfloor cat. The ceramic core in large or small pieces will quickly block the 2mm hex second core.
You have presumably had the maniverter replaced and the underfloor cat cleared of debris or replaced if the heat buildup has melted the core.
Has the garage run an OBDII diagnostic to confirm any recorded error codes?
Emissions, assuming judged on the same basis as the earlier cars centres around the first maniverter cat with the post cat lambda being just after the maniverter whereas the emissions at an MOT test checks what comes out of the exhaust exit.
The second, post cat lambda has no effect on emissions - it is a diagnostic sensor.
Emissions will be effected by the cats and the precat lambda.
I would suggest you get an error code reader and plug it in to you OBDII port and report any error codes.
Both the manifold cat and underfloor cat have been replaced now. This has cleared the blockage, and the car pulls and revs fully/freely. Only problem is the EML+emissions are still to high for MOT.
Local garage said they suspect the 1st cat is the problem (the one from mx5parts), but I pointed out that the 1st sensor has not been replaced - they did agree that this was worth investigating before the cat. I don’t know how mx5parts would handle a warranty claim, as it’s still within 30 days but obviously been fitted/used.
I think the error code is P2096 - this was from the main dealer that did the initial diagnostic, o2 sensor reading lean apparently. All the fault codes to my knowledge have come form the 2nd sensor. I can get the current fault code(s) tomorrow.
Down about £1200 so far for parts/labour, so I reckon the 1st sensor s worth a go, trying to get one from breakers/ebay, even if it’s just to see what happens!
EDIT - just had a message re an eBay breaker car - front cat + both sensors, I think this might be worth a pop. Is the cat the same for all mk3’s does anyone know, 1.8 or 2.0? Think this is from a 2006 plate.
The only direct faultcode from the front cat sensor would be if the heater circuit is open circuit.
A front sensor that is out of spec will give the incorrect reading to the fuel system that would either make the mixture too rich or too lean. The front sensor will not report other error codes.
It is the technician who has to make a decision on what needs replaced from experience. The diagnostic system is an assistance not a complete answer to what is wrong.
OK the upper O2 sensor has been replaced with the aftermarket part from Autolink, but the fault is still there. Light was off after the garage cleared it, but on the way home it came back on the first time I got the revs up >4k rpm.
Code is P2096 from the lower O2 sensor.
Local garage have advised that there is a possible ECU software fix for this, so I’ll contact the Mazda dealer.
I also have possibly an option to get a manifold cat with both sensors from a 2.0 NC but I’ll probably have to move quite quickly, and/or a manifold cat from user rodders.
Is this worth it, or should I get the dealer to investigate?
Lean mixture reading are caused in general by inlet manifold leaks and associated hoses etc also exhaust gasket leaks
you may also find you had a lean situation before the cat let go and this was the cause of your problems due to heating the cat too much due to the weak mixture and it breaking apart that way
of course im only speculating as i havent seen your car personally
also as already said the initial diagnostic code are just a basic direction not an absolute you need some more testing and measurements doing as thats when the real fault finding starts