Volvo: 1994 950 Nox emission failure, temp gauge, oxygen sensor

Question
Hi,

I have a 1994 960 with 92000 and it failed emissions for Nox (I think this is correct). I was told it was because the car is not driven on the highway often enough. The shop put in a mixture of something that should burn off the built up carbon so I drove it 200 miles on the highway and then it still failed Nox? I do notice the temp gauge comes up to the middle very quickly (in about 1/2 mile of driving in the summer) but then it never goes above that. The car runs great in all cases. Any suggestion would be most appreciated.
Thanks, John

Answer
Most people will tell you that the carbon buildup issue is mostly a myth, and I think you would be even harder pressed to tag it as the cause of your Nox failure.  Most likely it is an emissions sensor, like the oxygen sensor or catalytic converter.  Beacuse I'm not as familiar with the 900 series, I'm going to suggest you visit www.brickboard.com, and post your question for free in the 900 series section.  You should get a more specific recommendation from someone who owns a 960.  Good luck!