The Check Engine Light problem on CNG is only with cars having Emission Control system (Euro standards compliant). On Petrol and CNG exhaust composition is different and the Oxygen sensor on exhaust gives indication that there is something wrong with fuel. City IDSi 2006 and above may have this problem. Also note that Tomosato Lavato 5cip has built-in emulator for oxygen sensor but most of Tomosato available in market are China/ locally made.
