One problem related to gas recirculation valve (egr valve) has been reported for the 1999 Cadillac Concours. The most recently reported issues are listed below.
While sitting in front of my home my 1999 Cadillac deville caught on fire and burnt to a total loss. The car was parked, had not been driven for about 48 hours. The fire started in the engine compartment. The fire occurred at about 2:00pm. Satruday afternoon. Temp about 82 degrees. Something in the cars engine room on the left side ignited. It appears to have been an electrical problem that self ignited. Just prior to the fire, my wife who was at home at the time heard the car alarm go off. She went to the window and it quit sounding. She did not see any fire at that time. About 5 minutes later a neighbor pounded on the door and alerted her to the fact that the car was burning. The fire was so intense that before the fire department got to the seen, one of the hood gas struts blew through the front grill and landed about 20 feet in front of the vehicle. The fire department came and put out the fire. Something obviously within this cars engine compartment electrical/computer system started the fire. The car is a total loss. Cadillacs should not burn and should not spontaneously ignite. The car had about 75,000 miles. I own 11 other cars and have a small car collection. I am a car guy and this car like all my cars (including 2 Ferrari's) has been well maintained and when I last drove on Thursday evening August 28, it ran fine and did not give me any indication of any electrical issues. The police determined that it was not vandalized or caused by any outsiders.