Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) GDI OBD Fault Code

Would be grateful if anyone can tell me whether the car may have developed a problem or if its just one of those things.
The engine warning light came on a week or so ago, stayed on for a couple of days and then went out. It has now come on again and has stayed on. The code is PO420 which is 'Catalyst Efficiency Below Threshold Bank 1 ' which, according to the internet search means that is not as efficient as the factory is expecting, so either an O2 sensor or cat issue or the factory ECU setting is not quite right. Both times it came on the engine was under a lot of load, I was enjoying myself though!
I have cleared the code and it hasn't come back on again, yet, and the engine is performing normally. This used to happen quite frequently on my previous car, a Black Top Zetec 4/4, which sailed through its MOTs without any problems and performed as it should so I am thinking its just one of those Morgan features but would appreciate any comments from those who know more about this than I do or have had the same fault code on their GDI.

Sounds to me like your cat may not be getting hot enough. Drive it harder

Andrew,
I had precisely the same code from time to time with the completely standard GDI. It's just the downstream lambda sensor indicating low cat efficiency. Nothing to worry about. It usually happens in cold weather or if the car has idled for too long and the cat has not warmed up. I get it now with about the same frequency with my free-flow manifold and new 200-cell cat. As long as the car gets fully warmed up before its MOT it should pass.

Same code and symptoms on my 2008 +4 (2.0 Duratec) surprisingly Griffo Allon Whites said they have never seen a downstream Lambda failure as it's always the upstream? Logic says the code description would for sure mean the after Cat sensor and that's what had me confused. I noticed that my light comes on every time I am in slow moving traffic for a while or when booting it just after slow moving traffic and never when on a long high speed run so I concur with your analysis that the Cat has simply got cold/cool.

Last week moving around Dorset with 3 others and light constantly coming on, (I leave the lead connected and can clear it at traffic lights now ;-)) 175 miles of main and D/C roads home and no light showing....I shall leave until winter and then change both sensors, belt and braces and all that. ;-)

Here is the response I sent to a similar question from Colin:-

I had a problem with the MIL light coming on with our 2014 GDI +4. It would usually come on with gentle or long downhill driving and would usually (but not always) reset by the next day. The code stored had the same description as you have experienced. Anyway the front sensor was changed under warranty (after a long wait for a replacement) and all was well for a while. After a couple of months it came on again and although the reading was the same the dealer said it was now the other one. They changed the rear one within a few days (again under warranty) and the light has not come on again since and we have recently completed a run of a couple of thousand miles down to Provence and back.

Exactly John and your post convinced me to change both sensors at the same time, really helpful information.

Sounds like I have nothing to worry about.
The light came on in identical circumstances, once on the way to Devon and once on the way back, when I was in heavy slow moving traffic for what seemed like an eternity and then flat out acceleration on short uphill stretches of dual carriageway trying to get past as many lorries as possible before the single lane road started again, wife only swore at me once so she was probably asleep the first time.
Thank you for your replies.