Volvo: Intermittent engine cut out on 940 GL, catalytic convertor, oxygen sensor

Question
I know that my question relates to a 940 but you may well have come across the problem in the 240 and the remedy might be the same for both. Firstly, the Lambda light is continually on, secondly, the car will occasionally shut down without warning. When this happens the engine will turn over but not fire. It will always restart if I wait patiently for approx. 30 to 60 seconds. This occurs maybe four or five times a month. Furthermore, leaving the car parked in direct sunlight on very hot days means that it will not start at all until the cool of the evening. Do you have any suggestions please?

Answer
The Lambda Sond system is the emissions control they put in Volvos to reduce smog.  A light in that area indicates one of the components of that system is bad.  Based on your symtoms, it seems most likely to be the catalytic convertor.  When they get hot, and begin to break down, they restrict exaust flow and kill the engine.  Letting them cool usualy fixes the problem.  A second possibility is your oxygen sensor, which again will cause problems when hot and not working, but it's far less likely it would completely kill the engine when bad.  Usually they just make it run extremely rough.  My bets are on the catalytic converter, but have both checked out.  Good luck!