Hi all
on my 2005 MX5 mk3 NC 2.0, the EML came on Yesterday
I plugged a scanner in which threw up this code P0421 . Anyone else seen similar?
I kmow it’s related to the senors before and after the cat . Is it likely to be the cat or sensors? if a sensor, which one is likely?
or is there anything else I need to check?
Can I add the car is not modified in any way, but I do use option for local 4-5 runs with a motorway blast every week. I did a search on the forum and know it’s either one of 2 sensors, or the cat. Which would you change first?
I wouldn’t personally play the parts lottery but that’s up to you
if so cheapest first but it’s a catalyst efficiency code so likely hood is your cat is on its way out
if it was just the sensor you would have a sensor only code in general
you really need to get the rear sensor checked and the cat efficiency thou
any good place can do this for you and it doesn’t take long with the right kit
Cheers. this makes sense.
am investigating in investing in anew foxwell scanner for my other car (to wind back the EPB for a pad change) so will check it can scan for the sensors too . BTW, I agree about the parts lottery, which is why I asked!
The car has done 105k miles btw.
Long shot but on a cold day are you getting as much warm air from the heater as you have in the past. It can be an open thermostat.
I may have a low mileage cat that you could have for postage.
Possibly a failing front O2 sensor or the mass flow sensor.
They do not always throw up their own code.
Worn out Cat seems a reasonable assumption.
Faulty rear O2 sensor again they do not always throw up a code.
Double check all the wiring and clean connectors if you can.
How long does it take for the light to come on again after you clear the code with the code reader.
Thanks for the advice. The thermostat was changed in the autumn and the needle definitely moves further (and heater is warmer) so I think that’s ruled out.
really appreciate the offer of the CAT, good lad. But I will get the rest of the sensors scanned first to rule them out. BTW, my simple scanner knocked off the EML but I’ve not been out since so can’t tell yet when the fault returns. I will update when I use it tommorrow
It may well be that you only get the light on once a month or so. If that is the case just turn the light off whe required.
My EML came on regarding the EGR valve, I reset it andit didn’t come on again all year.
Same again the year after, came on once and never again.
Year after that, came on maybe twice.
Last year it came on twice within a few weeks, so I replaced the EGR.
If it’s infrequent, it might be as well to keep resetting it until it’s a definate fault.
Well, I did a 40 mile run today, no issues, EML still off.
Thinking about it, I was over a bit of bumpy track when it started so maybe theres a loose connection as a further possibility, to add to the sensors, and cat. I’ve ordered my new scanner today so,hopefully will be able to see exactly what’s caused it if it happens again.
I’ve had the car three years now, and given it was 12 years old with 98k then, it’s run perfectly with just basic maintenance .