The ignition key contains a transponder that transmits a signal to the theft deterrent module when the ignition switch is turned to the ON position. The theft deterrent module compares the signal from the key and determines if an authorized key is being used. During this period, the engine control module (ECM) turns on the malfunction indicator lamp (MIL) by grounding the control circuit. The MIL control circuit is monitored by the theft deterrent module. When the theft deterrent module senses the voltage change from the ECM grounding the MIL control circuit, the theft deterrent module switches the signal on the VSS/theft deterrent signal circuit from the speed signal to send the frequency code to the ECM. The theft deterrent module sends the frequency code to the ECM on the same circuit used to transmit vehicle speed information to the ECM. The ECM compares the frequency code with the learned frequency code. If the frequency code sent by the theft deterrent module matches the frequency code programmed in the ECM, the ECM allows the engine to start. If the codes do not match, the ECM disables the injectors to prevent the engine from starting.

Engine cranking

The theft deterrent password has not been programmed into the ECM.

The ECM will not illuminate the malfunction indicator lamp (MIL).