You should turn the ignition, use a scan tool to retrieve the percentage of remaining engine oil and automatic transmission fluid life, measure the main relay circuit voltage at the ECM/TCM/IGN fuse in the underhood fuse block and at the TCM/BATT fuse in the underhood fuse block, disconnect the negative battery cable, remove the TCM/BATT fuse from the underhood fuse block and the ECM/TCM/IGN fuse from the underhood fuse block, unlock and disconnect the front engine wiring harness electrical connector from the ECM and the rear engine wiring harness electrical connector from the ECM, release the locking tabs, remove the ECM from the ECM bracket, depress the locking tabs on the ECM bracket and remove the ECM bracket.