The lambda light indicates there is a fault with something in the emission system. There is no was to know what went south without the diagnostic hook-up through the eecm harness, located directly below the coin holder on the console. Just lift the rubber coin holder, and voila! The diagnostics computer will probably fetch $800-1,200 used, if you can find one with the Volvo program. If not, you can save lots of money by taking the car to the dealer, who will gladly (for a fee) hook it up, read the codes and make a recomendation for repairs. You have to tell them ahead of time you ONLY want DIAGNOSTICS. The code will tell you what broke, or is at fault. I suspect the O2 sensor (oxygen) located smack dab in the midle of the exhaust system. If you have under 100k miles on the car there are several pieces of the emission system that are covered under a federal emissions warranty. O2 sensors in some instances are. All are covered under 50k miles. When the codes are read, the light is usually reset.