HOW CAN I FIND AND FIX ENGINE LIGHT ON WITH VTM-4 LIGHT ON AS WELL

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Last week on Friday I noticed my Check Engine light on as well as the VTM-4 light. I check the manual. I redid the gas cap. After several drives and refilling the tank, they went off. I drove the entire weekend with no problem. Tuesday mornig this week they are both on again. I replaced the gas cap, no change. I had the oil changed, no change. I even diconnected the battery. The lights were off for about 30 minutes and are now back on. Thursday evening I noticed the "side airbag off" light is now staying on. The car has some other problems such as the doors no longer look/unlock by the electric buttons and must be done manually. The car seems to be driving fine. We do not have money for repairs and must have this car running. Is this something I can fix light a sensor replaced or something?