2003 chevy trailblazer wont start or crank but has power to the dash

Circuit Description (ECM/PCM Controlled)
Moving the ignition switch to the START position sends a 12-volt signal to the engine control module (ECM)/powertrain control module (PCM) Crank Request circuit. The ECM/PCM verifies that the transmission is in the PARK or NEUTRAL position. With the transmission in Park, voltage flows through the Park/Neutral position switch and feeds the starter relay coil. The PCM then grounds the control circuit of the starter relay. When the starter relay is energized it allows battery positive voltage to the starter solenoid S terminal. On some vehicles the starter will continue to crank the engine with the key released until it starts or the crank command has timed out to prevent excessive heat build up in the starter circuitry or the ECM/PCM receives an engine run flag.

Circuit Description (BCM Controlled)
Moving the ignition to the START position signals the body control module (BCM) that engine crank has been requested. The BCM verifies that theft is not active and sends a serial data message to the powertrain control module (PCM) requesting engine start. The BCM also energizes the RUN/CRANK RELAY. When the RUN/CRANK RELAY switch side closes, and the vehicle is in Park or Neutral or with the clutch is fully depressed, if equipped, supplies voltage to the starter relay coil. The PCM verifies the transmission is in Park or Neutral and the clutch is fully depressed, if equipped. The PCM will then ground the control circuit of the starter relay, closing the switch supplying voltage to the starter solenoid. On some vehicles the starter will continue to crank the engine with the key released until it starts of the crank command has timed out to prevent excessive heat build up in the starter circuitry or the PCM receives an engine run flag.

By reading this you should be able to comprehend the complexity of the starting system on your vehicle . It takes special tools (scan tools) an knowledge to dignose these type problems. Circuit Description (ECM/PCM Controlled) Moving the ignition switch to the START position sends a 12-volt signal to the engine control module (ECM)/powertrain control module (PCM) Crank Request circuit. The ECM/PCM verifies that the transmission is in the PARK or NEUTRAL position. With the transmission in Park, voltage flows through the Park/Neutral position switch and feeds the starter relay coil. The PCM then grounds the control circuit of the starter relay. When the starter relay is energized it allows battery positive voltage to the starter solenoid S terminal. On some vehicles the starter will continue to crank the engine with the key released until it starts or the crank command has timed out to prevent excessive heat build up in the starter circuitry or the ECM/PCM receives an engine run flag. Circuit Description (BCM Controlled) Moving the ignition to the START position signals the body control module (BCM) that engine crank has been requested. The BCM verifies that theft is not active and sends a serial data message to the powertrain control module (PCM) requesting engine start. The BCM also energizes the RUN/CRANK RELAY. When the RUN/CRANK RELAY switch side closes, and the vehicle is in Park or Neutral or with the clutch is fully depressed, if equipped, supplies voltage to the starter relay coil. The PCM verifies the transmission is in Park or Neutral and the clutch is fully depressed, if equipped. The PCM will then ground the control circuit of the starter relay, closing the switch supplying voltage to the starter solenoid. On some vehicles the starter will continue to crank the engine with the key released until it starts of the crank command has timed out to prevent excessive heat build up in the starter circuitry or the PCM receives an engine run flag. By reading this you should be able to comprehend the complexity of the starting system on your vehicle . It takes special tools (scan tools) an knowledge to dignose these type problems.