You can try having a smog check referee's office diagnosis your Volvo S40's check engine light problem. Referee stations are usually located at local community colleges and offer expert smog check diagnosis and repair for a reduced cost. Contact them at (800) 622-7733.
If you are unable to afford the required repairs you can apply to the Consumer Assistance Program. The CAP program will pay the STAR smog check repair station of your choice up to $500.00 in smog check repairs. If your Volvo still required further repairs the Referee's Office may allow you a one time two year hardship waiver.
Consumer Assistance Program