check engine light on 2001 BMW 330Ci

i just had my alternator, thermostat replaced and the parking break light, traction light, check engine light were on and the said they had to calibrate it?? its been 1 month and now my check engine light is on again these are the codes # 18 signal, camshaft sensor, exhaust second code # 204 plausibility, idle speed (air Leakage)

Asked by for the 2001 BMW 330Ci
If the alternator stops charging on many cars many dash warning lights can come on (e/brake, check engine, park brake and traction control light) but once the car is charging and the engine is running no dash warning lights should be on. Any time we replace an alternator we check the diode pattern and charging amperage and voltage of the installed alternator (some rebuilt alternators are junk!). The codes stored need to be investigated ask for the codes to be written down like P0420, or P1138 they are more specific trouble codes with specific trouble shooting charts available.