I have a 2003 Mitsubishi Pinin and the engine monitoring light keeps coming on and off. Mostly it is on, but can go off for about 50 to 100 miles before it comes on again. I've had it checked by a Mitsubishi dealer and each time it gives an error code of P0421Warm-up Catalyst Efficiency below threshold (Bank 1). The emissions are OK and both oxygen sensors have been replaced. After a Google search I was going to try the fix suggested by http://www.club3g.com/forum/performance/55284-how-fix-ses-error-code-p0421-about-5-bucks.html but find the spark plug antifoulers are not available in the UK. Also would it be legal? I've now got used to ignoring the light, but has anyone got any other ideas?
Error code P0421
- Thread starter umborne
- Start date
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Thanks. I remember finding this site as well, but wasn't sure what to make of it. The oxygen sensors are both new and the emissions are OK implying the cat is working properly. I haven't looked at a spark plug, but any fouling ought to be reflected in excessive oil consumption of which there is no sign.
change the plugs and take it for an italian tune up,you wont notice any excessive oil consumption with fouled plugs
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I had the same problem on my Zafira for the last 2 years, except that the light stayed on constantly (Po421 heated catalyst below ........) . after changing several sensors and the cat (which had no catalyst) it finally turned out to be the flexible joint on my exhaust's front section. £40 and 3 months later and the light has stayed off.