Anyone experience of the why the Cat light comes on and then goes off, for no reason? I gave the car a 'spirited drive' yesterday and then while waiting at a junction the light came on, then went off about 10 mins later. It was fine when used firsts thing today, now the lights on permanently. Its a 1990 C2.

chris

 

Chris,

I'm confused - because I didn't think any of the RoW cars HAD a Cat warning light!! A picture would be useful to identity which light you are talking about. I think one of the warning lights does have "CAT" written on it but, as I said, I don't think it's wired on a RoW car.

Dave

 

Hi Dave, the car is a Jap import with a Cat fitted, the warning light is the next one (clockwise) after the seat belt light.

chris

 

OK - I guess that would explain my confusion at least. I'm afraid I've no idea what activates the CAT light though. The only bit of electrics that I'm aware of in that area is the O2 sensor so it's possible that the light might be some indication of a malfunction of that. It's possible that the DME might indicate if the signal is out of range or something similar. My best guess I'm afraid.

Maybe someone else might have a better idea.

Regards

Dave

 

Thanks Dave, I suspect its on the way out I had a similar problem with a 348 which managed to blow the Cats clean out the exhaust. Bypass pipe next..

chris

 

Normally, the 964 ECU will only monitor the oxygen sensor and not the cat so a warning would signal a problem with O2 sensor. UNLESS you have a japanese model in which case the ECU also monitors the temperature inside the cat. However, I think that temperature measurement is used by the ECU to control open & closed loop and not for keeping the cat in the proper temperature range (estimating cat efficiency/life/.etc). In a ROW/USA ECU the system will estimate the temperature inside the catalytic converter by using a combination (think of it as a virtual sensor) of the CHT sensor and a timer. When the system thinks the cat is hot enough to function properly it will start to use the O2 sensor to control the fuel mixture. I vaguely remember Japanese law requiring actual temperature measurement but I would have to look it up again. (I don't have a Japanese model ECU to examine disassembled ECU code either) So your problem is most likely related to the O2 sensor or the cat temperature sensor and not the catalytic converter itself.

 

Jason, it is a Japanese spec car and the waring light activation corolates to the temp of the car, suburban driving its on/off depends however, on an open road, floor it and light goes out for good. There is a sticker on the drivers door bin to do with Cat temp but my Kanji is a little rusty. And yes your right Japanese law does require temp measurement.

You clearly know your stuff, so a question - Can I fit a Cat bypass with just an O2 sensor and loop the temp sensor?

thanks

Chris