Hi All,
Ive had the warning light come up twice in about 500 miles. each time im able to clear before it comes on again after a long run. Car needs a service so will get it investigated if I cant sort myself. Just wondered if there is anything I can check / try
Warning is : - P0420 Catalyst System Efficiency Below Threshold. Bank 4 cat depleted or insufficient.
It did recently ‘fail’ an MOT due to emissions which is probably related I guess.
Are you running a decat?
Ideally it wants someone better than me but that sounds like a failing o2 sensor.
Cars only done 18k so I was doubtful of a failed cat but not sure if they deteriorate over time rather than use.
Could be the sensor, they do fail from time to time.
Ok, on another thread I’m changing the back box so had a look at the cat at the same time. It’s empty is the cat pipe. And I found this in the back box.
So what are my options? I presume if I put spaces on the o2 sensors I will prevent the warning light coming on, but I’ll fail a mot. Also, will the car be running rich/lean? I’m unsure as to the point of the o2 sensors? Is it to adjust the fuel mix or just to check there’s a difference between pre cat and post cat.
Should I just buy a cat. I see lots of people buying de cat pipes for other cars…
Cat collapses seem to be coming more and more common on SC S2 cars. I’ve known of 3-4 in my “immediate circle” of Lotus friends/family that have suffered it in the last year or so.
The SC 2ZZ is not really limited by a healthy catalyst whilst you’re within the capabilities of the stock supercharger, so you don’t really have much to gain by staying decat. Anecdotally people report a sharper throttle response and stuff like that, but you never know how much of it is down to placebo and the extra noise the car will be making!
The factory O2 sensors are just narrowband, so yeah they’re just looking for a difference in reading post/pre cat. Lotus MS were known in some instances to run just a pre-cat sensor (the 2-Elevens are like that at least) but I’ve got no idea how that’s actually supposed to work.
You can get away with a sensor spacer which should stop the error in most cases, but you should probably always travel with a code reader just in case, and yes it will fail a legit MOT.
Your options really are:
1- Commit to decat, car will be a bit louder, will have MOT troubles, might feel a bit sharper? Cheapest option
2- Look out for a used Lotus catalyst, they come up occasionally in the £3-400 range but you might run into this problem again in future
3- Go Aftermarket and swap the system out for a sports cat. I don’t have universally good things to say about 2bular but one thing I will say is that my 200cel sports cat has survived across two different 2ZZ cars, both of which running fairly aggressive states of tune and touches wood is showing no signs of degrading. Still flies through an MOT legitimately. Expect to spend a few grand on this approach for a decent setup, though.
Oh, there are also electronic engine light ‘eliminators’. I have no experience with them, but I guess they’re more consistent than a mechanical spacer is.
I would go down the sports cat route personally. I used a komotec one thats a 200cel cat ( so passes mots ) and is a decent brand cat inside the pipe.
Thanks for the comprehensive reply @Fonzey and explanation of what the o2 sensors are doing. I recall having a conversation with someone a few years back, all-be-it about a different car and they told me that the sensors can adjust the fuel mix and if aren’t working right could run lean/rich and melt the valves. Probs BS but best to check
Car gets limited use at the moment so I think I’ll keep my eyes peeled for a used and save for a full replacement while looking. Short term I’ll bang some spacers in, if I can find some and carry the ODB widget with me. That said, the cars doesn’t go into a limp mode so I could just live with the light.
If its not replaced by MOT time ill have to hope it ‘passes’ again. 
