I have a 2002 cadilac deville the air bag and traction lights came on and the gas gauge was not showing on. I stopped cut car off and crank up with only traction light on. Drove to work cut off then on everything workin fine. Come from break tried lockin from remote would not lock from temote or door. Tried crankin would not turn over but headlights and dash lights on

Do you know how to do electrical testing using a wiring diagram and a DVOM - digital volt ohmmeter ? Do you know how complex the electronic's are on your vehicle are . Could be something simple but then again may not be . Hooking up a professional type scan tool that can check for DTC'S in all the modules on the vehicle would be the first step in diagnosing this ! Do you know what a electronic control module is ? Your vehicle can set hundreds of code's an they don't all turn on the check engine light . Moving the ignition switch to the CRANK position sends a 12 V signal to the PCM Ignition Crank Sense. The PCM verifies that the transmission is in the PARK or NEUTRAL position. The PCM then grounds the control circuit of the START relay. When the START relay is energized it allows voltage to the starter solenoid S terminal.Do you know what Data Link Communications are ?
The data link connector (DLC) allows a scan tool to communicate with the class 2 serial data line. The serial data line is the means by which the microprocessor-controlled modules in the vehicle communicate with each other. Once the scan tool is connected to the class 2 serial data line through the DLC, the scan tool can be used to monitor each module for diagnostic purposes and to check for diagnostic trouble codes (DTCs). Class 2 serial data is transmitted on a single wire at an average of 10.4 kbps. This value is an average; class 2 uses a variable pulse width modulation to carry data and depending on the message it may operate faster or slower. The bus will float at a nominal 7 volts during normal operation. Each module can pull this lower during the transmission. The bus is not at battery positive voltage or ground potential during normal operation. When the ignition switch is in RUN, each module communicating on the class 2 serial data line sends a state of health (SOH) message every 2 seconds to ensure that the module is operating properly. When a module stops communicating on the class 2 serial data line, for example, if the module loses power or ground, the SOH message it normally sends on the data line every 2 seconds disappears. Other modules on the class 2 serial data line, which expect to receive that SOH message, detect its absence; those modules in turn set an internal DTC associated with the loss of SOH of the non-communicating module. The DTC is unique to the module which is not communicating; for example, when the inflatable restraint sensing and diagnostic module (SDM) SOH message disappears, several modules set DTC U1088. Note that a loss of serial data DTC does not normally represent a failure of the module that set it.

Your best bet would be to have a qualified repairs shop check it out .