90 300se Cel
 

Hi,

My check engine light has come on for about 6 months, but there was no code from the push button/LED on the firewall. I held down the button for few sec and the LED lit, but no flash after the button was released. I know the LED worked before (a few year back)... it flashed 16 for EGR, which was then fixed.

I could reset the CEL by unhooking the battery, and it would come back in a few days. The car seems running fine.

It is now time to take the car to smog check, and I try not to have to take the chance of having the light come on during the test.

I went through the related pages in Alldatadiy, but I could not tell if there was another place to hook up a pulse monitor. I appreciate any help or suggestions.

Thanks
Kachun

90 300se
 

about the only thing that the cel was for back in 90 was to warn of problem with o2 sensor.if the ecu did not see a changing voltage over a period of 10secs it would bring on the light.this could be one of 4 things.[1] system has vacuum leak and so very low voltage[2]system is running too rich[.900 volts][3]o2 sensor disconnected.[4] o2 sensor defective.hope this helps.

Thanks for the info. I take that you meant the O2 sensor was the one event that you thought could light up the CEL without throwing a code.

I did checked the 02 sensor with a scope on the X11 connector. The on/off ratio was in range at both idle and high RPMs, so the chance was high with intermit cable/connectors. I will recheck all the connections. Well, it is way passed 60K miles with my current O2 sensor, maybe, I go ahead and replace it.

Thanks again