Engine 850: B5234T/2.3/20v/T5: Engine Management Light

[stevepcar]

I left my MAFF unpluged by mistake recently for about 20 minutes while I was trying to check my auto gearbox & coolant levels I eventually discovered it & plugged it in. At some point the engine warning light had came on & the codes it threw up w 2:3:1. & 2:3:2. I tried clearing the codes, thinking that computer was taking it's time acknowledging that I had plugged the MAFF back in. The light refuses to go out. I have tried a smoke test & spraying carb cleaner over everything, but no vacuum leaks are showing up. When I first started this restoration the car had been stood for 7 years, with occasional starts, after it had failed MOT on a suspected faulty Cat or O2 sensor. I eventually got it through by pouring Cataclean into the tank. Since then I have had to change the PCV as the EML came on, & the Auto Transmission as it was slipping. That was successful, but now I am back to where I started with the EML.
Can an O2 sensor work intermittently, or does it fail completely? I am guessing that a Cat is bad or it isn't? Any ideas or advice greatly appreciated. I am going to test the O2 sensor by heating & checking how it behaves with a voltmeter. Is this a reliable method?

[Clogs]

Sadly you often need a good couple of runs to get the computer back to normal which isn't really possible now. After a few good burn ups, perhaps your OBDII meter will be able to clear the codes.

Are you saying there are no codes at the moment?

[stevepcar]

I get 2:3:1 & 2:3:2. I have tried clearing them but no joy. I am thinking of a good burn up on the way to the shops, as I think this has happened before. I believe the computer takes time to compute how the car is running & eventually it readjusts the fuel ratio back to before I unplugged the MAFF sensor. Fingers crossed.

[downstream]

Originally Posted by stevepcar

Can an O2 sensor work intermittently, or does it fail completely? I am guessing that a Cat is bad or it isn't? Any ideas or advice greatly appreciated. I am going to test the O2 sensor by heating & checking how it behaves with a voltmeter. Is this a reliable method?

O2 sensors can start to go bad without necessarily throwing an error code... I think the quoted service life is 100000m / 160000km? So it's worth replacing if you have no record of it having been changed previously...

[ASt85]

Originally Posted by downstream

O2 sensors can start to go bad without necessarily throwing an error code... I think the quoted service life is 100000m / 160000km? So it's worth replacing if you have no record of it having been changed previously...

Also, they can be damaged by excessive oil in the fuel too - which most often after a ragged poor or misfire start.

[stevepcar]

Well a good burn up round the ring road did the trick. I did about 15 miles then switched off the engine. When I re-started it the EML was still on, so I switched off and cleared the codes. When I strted it again the light went off, so the computer just took it's time. Just need to replace the oddometer gears, rear tailgate struts, blah blah blah the usual.

[ASt85]

Originally Posted by stevepcar

Well a good burn up round the ring road did the trick. I did about 15 miles then switched off the engine. When I re-started it the EML was still on, so I switched off and cleared the codes. When I strted it again the light went off, so the computer just took it's time. Just need to replace the oddometer gears, rear tailgate struts, blah blah blah the usual.

AKA a forced reset....ie an Italian tune-up!

For the uninitiated a blast down an autostrada @ max signed limits has a wonderful clearance value, as does an autobahn...just that in Italy it is a whole lot more fun - especially if it is a C70 with the roof down....probably why I've lost a lot of head hair........