If the MIL lights continuously, there is malfunction that affects exhaust emissions. In this case the DTC memory of the ECM and TCM must be checked and the malfunction must be corrected as soon as possible.
Some malfunctions may occur without causing the MIL to come on. When driveability or performance problems are reported and there is no indication from the MIL, the operation of the MIL must be checked. In addition, the DTC memory of the ECM and TCM must be checked, as there may be malfunctions stored that do not switch the MIL on immediately.