My 1997 Volvo 850 just flunked a California smog test. The NO emissions at 15 mph(472 ppm) were about 10% higher than the maximum allowed (424 ppm). Interestingly enough the NO emissions at 25 mph (434 ppm) were considerably LOWER than the maximum(711 ppm). I phoned my Volvo repair shop, and they said, “You definitely need a new catalytic converter, which will run you $1,600 plus tax and labor”. Is there anything other than a catalytic converter that might be wrong here and might cost me less to repair?
It is possible that your EGR valve is stuck and is causing higher than normal temperatures in the cylinders. It is also possible that your ignition timing is “off”, but I don’t know if the timing is adjustable on a '97 Volvo.
Before I invested in a new catalytic converter, I would have the EGR cleaned or replaced, and I would replace the spark plugs. Either or both of these things could help you to pass the NOX test.
Thank you, VDCdriver.
One of the passages to and from the EGR valve could also be clogged.
It should also be pointed out that you likely can get a new converter from an independent mechanic for a lot less than the dealer is asking. The converter may be from a third party manufacturer, but that is fine.