Howdy everybody.

The Check Engine light came on this week in my '92 940. The car has 160k miles.
I checked the code and it is 2-1-2,Oxygen sensor signal missing or faulty Oxygen sensor.
I checked the readings on the O2 sensor with the engine at operating temperature and they varied between 0.026 and 1.261 volts.
Is my O2 sensor bad? The engine runs fine, except at idle. Theidle isn't as smooth as it was before the Check Engine light came on.

Thanks.

 

Did you clear the code?

 

I did once and it came right back.

 

Do you have an exhaust leak or a vaccum leak?
The sweep is good on the sensor.
Maybe intake manifold gasket bad.

 

As a matter of fact, I noticed a slight leak at the manifold to exhaust pipe joint yesterday when I was testing the sensor. I tried tightening the nuts on the manifold and they were all plenty tight.

 

They are kind of known to warp. You might need to double gasket the joint.

 

Would an exhaust leak cause the 2-1-2 code?

 

That leak should be before the O2 so yes it will throw the code. But still check for an intake leak as well.

 

Update; I removed the exhaust pipe and, using a belt sander, smoothed the flange mating surface on the exhaust pipe. On the exhaust manifold I used a block with 80 grit sandpaper to clean that surface. I used a new gasket and high temperature sealant.
So far, the leak seems to be fixed. (fingers crossed)
I cleared the code. It hasn't come back.
Thanks.