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Norinradd working on a modern computer controlled car without a code scanner is like working on an old car with your eyes closed. ECU controlled cars are pretty easy when you have the correct tools for the job, the diagnostics in the onboard computers will most often point you in the right direction.
You rearly need to get that code reader or preferably android torque app running as it will read and reset codes and also allow you to monitor basic functions like measured AFR, Target AFR, ignition advance, Fuel trims, coolant and oil temps 02 sensor reading , intake air temps Mass Air flow MAF readings , and heaps of other stuff. Without that your just working blind and its very frustrating.