The code P0171 can be caused by a dirty or bad mass airflow sensor or vacuum leaks. The bulletin T-SB-0086-16 explains an issue in the 2014-2016 Corolla where the fuel tank filler neck that is out of position might cause the gas cap not to close properly. As a result, the Check...
A low coolant level can cause overheating of the engine and expensive repairs. If the coolant level looks very low, have the vehicle checked for coolant leaks before it causes problems. The code P0138 is often caused by a bad rear or downstream oxygen sensor. Replacing the rear O2 sensor i...