I've been trawling the threads (e.g. https://www.mr2roc.org/index.php?topic=67682.75) to see if there is something the same as my scenario, but nothing is jumping out
My car had a brand new cat fitted about 4 months ago and has started to flash up the EML.
The error code it is returning is P0420 "Bank 1".
If I reset it using Torque Pro, it is fine for a week or two (multiple 3-5 mile trips almost every day).
The cat was fitted by Pat Chambers, so I am assuming that installation isn't a problem.
O2 sensors are old, so it's a fair guess that need replacing.
Questions:
1) is there anything I should be checking as per the thread above before replacing sensors?
(that thread seems to be all about a failing cat, but if mine is brand new, I'm not sure if I'll get any useful info from a failing sensor?)
2) With that error is it just the lower one or do I need to do both the manifold sensors too?
3) Denso part numbers?
Googling around I think they are these two: Denso 234-4624 and 234-4603
Hoping to get away with just the lower one at this stage **fingers crossed**
Note I've got the TTE exhaust and ToyoSport manifold, but I've had these two combined without issue for most of the last ~10 years!
Check for leaks at the manifold to cat joint.
Is it a proper type approved cat or a 200 cel 'sports cat'?
The post cat sensor will have been subjected to a bit of a hammering removing it from the old cat and these sensors are quite delicate, but I would check for leaks before spending the money.
The other two sensors should be fine.
This is your likliest cheapest option. https://www.ebay.co.uk/itm/266231049216?fits=Car+Make%3AToyota&_skw=Denso+universal+o2+sensor+toyota&epid=18039424586&itmmeta=01KRF0BG53J0QV65NYMTPHTF36&hash=item3dfc9b6c00:g:HV0AAMXQMmJRS1E0&itmprp=enc%3AAQALAAABAGfYFPkwiKCW4ZNSs2u11xDtvEwGHAsRT3cutmY3f7wowoqzCW%2BUw%2F1yLB9mYpM1P6MSof4lAfBlu8IgWuZcmTdEpx5%2B7QUFG6zywX6km2RbOL%2F2RZFNiAn3cP1Hwi3ZIDnXcunJT%2FYdf%2FtmwiSCudFZXaIuAJwNx0Xsn7r3rAWFN1VRGyxt2J5AEk9ywkjXRB0hzRMrWxrWmEywmXf3weJBfavwkX%2BbvCGYnYJ9afvOCjO7rNxxHXzzbvF5lfaYRaPXBqBzi23e4afdDNcKivTuByiXRbMTLUg%2FcvBN8Zfhu1OHBr%2FqQYfWoHiR%2B9ZzliGdq3hGOiS9HIP659brIgM%3D%7Ctkp%3ABk9SR_iCruDDZw
Check ECP though, sometimes they have good prices on them.
Bear in mind the sensors are all the same, you just need 4-wire, thread fitting, Toyota plug & a long enough cable.
I've found a fe 'bargains' on ebay over the years.
Quote from: Gaz mr-s on May 12, 2026, 22:16This is your likliest cheapest option. https://www.ebay.co.uk/itm/266231049216?fits=Car+Make%3AToyota&_skw=Denso+universal+o2+sensor+toyota&epid=18039424586&itmmeta=01KRF0BG53J0QV65NYMTPHTF36&hash=item3dfc9b6c00:g:HV0AAMXQMmJRS1E0&itmprp=enc%3AAQALAAABAGfYFPkwiKCW4ZNSs2u11xDtvEwGHAsRT3cutmY3f7wowoqzCW%2BUw%2F1yLB9mYpM1P6MSof4lAfBlu8IgWuZcmTdEpx5%2B7QUFG6zywX6km2RbOL%2F2RZFNiAn3cP1Hwi3ZIDnXcunJT%2FYdf%2FtmwiSCudFZXaIuAJwNx0Xsn7r3rAWFN1VRGyxt2J5AEk9ywkjXRB0hzRMrWxrWmEywmXf3weJBfavwkX%2BbvCGYnYJ9afvOCjO7rNxxHXzzbvF5lfaYRaPXBqBzi23e4afdDNcKivTuByiXRbMTLUg%2FcvBN8Zfhu1OHBr%2FqQYfWoHiR%2B9ZzliGdq3hGOiS9HIP659brIgM%3D%7Ctkp%3ABk9SR_iCruDDZw
Check ECP though, sometimes they have good prices on them.
Bear in mind the sensors are all the same, you just need 4-wire, thread fitting, Toyota plug & a long enough cable.
I've found a fe 'bargains' on ebay over the years.
Literally just bought a Celica item with a long lead as fitting a zero manifold so need longer lead. Found new old stock Denso item on eBay this week at great price.
Quote from: SurreyMR2 on May 13, 2026, 07:18Literally just bought a Celica item with a long lead as fitting a zero manifold so need longer lead. Found new old stock Denso item on eBay this week at great price.
Bravo! ;)
Quote from: Carolyn on May 12, 2026, 16:24Is it a proper type approved cat or a 200 cel 'sports cat'?
Def not 200 cell sports cat.
@headcase said he was shopping around for one of the older spec ones (cheaper), but ended up going for the "approved" 2006 spec one.
I put a very good quality 200cell cat on and that avoided the P0420 mostly. But for MOT it needed SEVERE ragging and heat before passing. Like, crackling when stationary hot. Granted I had fiddled with stuff so fueling was never perfect.
Eventually I put a spacer in between sensor and cat just to avoid hassle.
But that was a mucho pricey custom cat. A cheaper 200 will 100% lead to P0420, and a cheaper 400-600 cell will 50% lead to P0420. 800 cell and up is your only safe bet to definitely avoid that. Stock is something like 1200cell
My partner bought a 2zz-compressor engine with a Rogue-built sports cat exhaust around 6 years ago. It's approx two years older than that.
A dose of Cataclean before the MOT & it breezes through each year.
pretty sure mine is a stock spec cat
I replaced the lower sensor, let's see how it goes...
If it's the original cat, it could well be at its sell-by date.