2001 Chevrolet Impala Engine Code Lights

I have had the car since new, and taken very good care of it (normal maintenance.)
Around 225,000 miles, my dash has lit up like a Christmas Tree! Even the air bag light is on. Other than the car jerking from time to time, the car runs fine. My mechanic put it on the diagnostic machine and the following numbers come up: 742, 420, 341, and 128. I there is probably no more than 15,000 miles on the rebuilt transmission, and 30,000 miles on a rebuilt catalytic converter. The car is not burning or leaking oil or antifreeze. Any help you can offer would be much appreciated. I am a senior citizen on a very low income. I cannot afford a new car, and no one seems to know how to fix the problem of the lights coming on. Please help. Many thanks. Steve Vida