Emissions (engine) Light

My MPV "check engine" light keeps coming on. After repeated inspections and varying readout codes, the emissions folks haven't a clue. I need to pass an emissions test to get my vehicle registered!

what was the trouble code?

A model year, engine size, and mileage will also help. Is the light being turned off and then comes back on or just cannot get to go out also?

Started with a fault code of P9421. Had the air filter changed; light was out for about 5 miles. Brought back in and read out a different fault code (unknown). Light was turned off; within 5 miles it was back on. Prior to this most recent incident, (Oct. 2004) responded to engine light by replacing IRCM. (Sorry, that's all it says on the paperwork.) The MPV is a 2000 with 96,000 miles. Have a very recent tune up.

Well am probably not going to be of much help but maybe we can make a start. There is not a P9421 although there is a P0421 that would point to a right side front catalytyic converter not operating correctly. This only applies to California emission vehicles as Federal do not have individual coverters. Would not expect this to come back after only 5 miles as it usually takes quite a while for the self test to rerun. Driving conditions must be met in order to self test. IRMC sound like a possible IMRC (intake manifold runner control) fault of which three codes could be set for a fault here P1512, P1518, and P1520. Is there any way you can go to a local parts store that checks codes for free and see what the currect code could be. Would be of great help.
Also do you notice any abnormal way the engine is running or driving.

Yes--P0421 is right. I'll try Saturday to find a parts shop in Washington State that offers the free service. Regarding the engine--it runs rough on accelleration (lower end) and on ocassion when the engine is idled the tach needle jumps (with no obvious rhythm).

Think you might be having a missfire code of some kind. P0300-P0306. Is one of the few things that will turn the MIL on that quickly. When the light comes on does it flash at any time or just come on solid and stay on?

Light stays on solid.

Any luck on getting a code inashell? Hadn't heard back from ya for a while.

I have the exact same problem and error code P0421 with my 1999 626. Rough idle and rough accel. Light sometimes will just blink, and sometimes will stay on for a day or so. More of a problem when its cold or wet out.
Any ideas on what is causing this problem? Thanks in advance.

I cannot comment on the specific problem of the driveability concern...but when you have a blinking check engine light it usually means its running rich or bad misfire. And its in the process of causing severe catalytic converter damage. So it needs to be addressed immediately.

bkey71 right on with the flashing CEL. If the CEL is flashing it indicates a potential catalyst damaging missfire. The p0421 is often right behind as this is a CAT efficiency code. You should also have some kind of missfire code being stored along with the P0421 such as a P0300,P0301,P0302,P0303,P0304, P0305,P0306. Are any of these codes also being set? These are missfire codes and if the light is blinking at least one should have been stored as well. Would look first to the plug wires and spark plugs as potential source of the problem as is fairly common, especially on the 4 cyl engine given your description.

You were right on the money. I pulled those plug wires out from the spark plugs and found out they had collected some fine dust/dirt. I found that two of the four plug wires had small discolored traces running down to the head on the inside of the boot. I cleaned them up and my engine is running like new again. Thanks again for all of your help.