What does front body module do

The light switch reports to the body control module. The BCM tell the front control module in the Integrated power module (IPM) to provide power. So check for power and ground in each bulb socket. If you see ground but no power, suspect a bad front control module or a bad IPM. Both are known problems.

Could be bad ignition switch or some other type electrical problem . Knowing how this system works on your vehicle is the key . The ignition switch is a low voltage input to the BCM - body control module . Depending on key position the BCM knows what relays to energize and what messages to send over the GMLAN serial data net work , PCM - engine computer . Hooking up a factory or some other type professional scan tool to view ignition switch inputs to the BCM , an checking for BCM DTC'S - diagnostic trouble codes .

Circuit Description
Moving the ignition switch to the START position signals the body control module (BCM) through discrete inputs from the ignition transducer that engine crank has been requested. The BCM verifies that theft is not active and sends a serial data message to the engine control module (ECM)/powertrain control module (PCM) requesting engine start. The ECM/PCM receives a 12-volt signal from the park/neutral position (PNP) switch or clutch pedal start switch notifying that it is safe to start the engine. There is a splice on this circuit in the fuse block-underhood that supplies power for the starter relay coil. The starter relay coil control circuit is then grounded by the ECM/PCM closing the switch in the starter relay suppling 12 volts to the S-terminal of the starter. Ground is supplied through the engine block.


Plus you need to under stand what power modding is , because the BCM is the power mode master . This will sound funny to someone who does not know about automotive electronics .
Serial Data Gateway
The body control module (BCM) in this vehicle functions as a translator between the High and Low speed GMLAN busses. The 2 communication protocols use the BCM to translate communicated serial data messages between the control modules over the 2 serial data busses.
Power Mode Master
This vehicles body control module (BCM) functions as the power mode master (PMM). Refer to Power Mode Description and Operation for a complete description of power mode functions.

Power to many of this vehicle's circuits are controlled by the module that is designated the power mode master (PMM). This vehicle's PMM is the body control module (BCM). The PMM controls which power mode (Run, Accessory, Crank, Retained Accessory Power, or Off) is active.

On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle, the PMM is the body control module (BCM). The PMM receives 3 discrete ignition switch signals to differentiate which power mode will be sent over the Serial Data circuits. The 3-wire Ignition Switch table below illustrates the state of these inputs in correspondence to the ignition switch position:
Relay Controlled Power Mode
The body control module (BCM) uses the discrete ignition switch inputs Off/Run/Crank, Accessory, and ignition 1, to distinguish the correct power mode. The ignition 1 circuit is also routed to the Run/Crank relay for relay controlled power feeds during the appropriate power mode. The BCM, after determining the desired power mode, will activate the appropriate relays for that power mode.

Knowing how it works is key , the ignition switch is a low voltage input to the BCM - body control module . When the BCM see's start input it sends a message over the serial data network to the PCM / ECM - engine computer . When the engine computer reads this message it will energize the crank relay sending B+ voltage to the S terminal on the starter solenoid ,there by cranking the engine . Taking to a qualified repair shop that has a factory or professional scan tool to read BCM DTC'S - diagnostic trouble codes is what you should do , before you cause more problems .

Circuit Description
Moving the ignition switch to the START position signals the body control module (BCM) through discrete inputs from the ignition transducer that engine crank has been requested. The BCM verifies that theft is not active and sends a serial data message to the engine control module (ECM)/powertrain control module (PCM) requesting engine start. The ECM/PCM receives a 12-volt signal from the park/neutral position (PNP) switch or clutch pedal start switch notifying that it is safe to start the engine. There is a splice on this circuit in the fuse block-underhood that supplies power for the starter relay coil. The starter relay coil control circuit is then grounded by the ECM/PCM closing the switch in the starter relay suppling 12 volts to the S-terminal of the starter. Ground is supplied through the engine block.

To understand how this can happen you would need to know how it works . Do you know what happens when you turn your key to start ? First you need to know this . Computer controlled systems. The ignition switch is a low voltage input to the BCM - body control module , the BCM energizes relay's to power up vehicle systems .

.Circuit Description
Moving the ignition switch to the start position signals the body control module (BCM) through discrete inputs from the ignition transducer that engine crank has been requested. The BCM verifies that theft is not active and sends a serial data message to the engine control module (ECM) requesting engine start. The ECM receives a ground signal from the park/neutral position (PNP) switch or a signal from the clutch pedal position sensor notifying that it is safe to start the engine. Ground G105 supplies ground for the CRNK relay coil. The starter relay coil control circuit is then supplied voltage by the ECM closing the switch in the starter relay suppling 12 volts from the CRNK fuse to terminal A of the starter. Ground is supplied to the starter solenoid through the engine block.

Power to many of this vehicle's circuits are controlled by the module that is designated the power mode master (PMM). This vehicle's PMM is the body control module (BCM). The PMM controls which power mode (Run, Accessory, Crank, Retained Accessory Power, or Off) is active.
Serial Data Power Mode Master
On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle, the PMM is the body control module (BCM). The PMM receives 3 discrete ignition switch signals to differentiate which power mode will be sent over the Serial Data circuits. The 3-wire Ignition Switch table below illustrates the state of these inputs in correspondence to the ignition switch position:


Your best bet , take it to a qualified repair shop .

what do I try next? You take your vehicle to a qualified repair shop. You have no idea of the complexity of the electronic's on your vehicle . Disconnecting battery cables an touching them is not the answer . Having a qualified professional with proper diagnostic tools checking computer system's is . One bad module on the GMLAN serial data network is all it takes for a no start . You have no idea what happens when you turn the key to start your vehicle.

Circuit Description
For ignition switch power modes refer to Body Control System Description and Operation. Once the ignition is placed in the Run/Crank position, the control circuit of the Run/Crank relay is grounded by the body control module (BCM). With the Run/Crank relay switch closed, battery positive voltage flows through it and on to the park/neutral position (PNP) switch. With the PNP switch in either the Park or Neutral position, battery positive voltage will flow to the starter relay coil supply voltage input terminal of the engine control module (ECM) and the coil side of the starter relay. Placing the ignition in the START position sends a message to the engine control module ECM requesting engine start. If the ECM has determined that the transmission is in Park or Neutral and theft is not active, it will ground the control circuit of the starter relay. Battery positive voltage will then flow through the switch side of the starter relay to the S terminal of the starter solenoid, cranking the engine.

Also with power steering warning on ,DTC'S are stored in the control module for the electric power steering an or the BCM - body control module . I have seen bad power steering control modules short out the data bus (network) .
Do yourself a favor an take it to a qualified repair shop.

I imagine you checked the fuse.

Sounds like it could be the ignition module in the distributor. You have a throttle body instead of a carb. The injectors get a ground signal from the engine computer when they are supposed to open. The ignition module takes a signal from the pickup coil in the bottom of the distributor and decides when to fire the plugs and also the injectors.
If the injectors and the coil has power, it could be the module or the pickup coil.

Without trouble shooting ,would only be guessing . Could be any number of thing's . You have no idea the complexity of the electronic's on this vehicle . All the different control modules , serial data communication network . You probably don't even know what's happening just turning the key to start the start position .
For ignition switch power modes refer to Body Control System Description and Operation. Once the ignition is placed in the Run/Crank position, the control circuit of the Run/Crank relay is grounded by the body control module (BCM). With the Run/Crank relay switch closed, battery positive voltage flows through it and on to the park/neutral position (PNP) switch. With the PNP switch in either the Park or Neutral position, battery positive voltage will flow to the starter relay coil supply voltage input terminal of the powertrain control module and the coil side of the starter relay. Placing the ignition in the START position sends a message to the engine control module (ECM)/powertrain control module (PCM) requesting engine start. If the ECM/PCM has determined that the transmission is in Park or Neutral and theft is not active, it will ground the control circuit of the starter relay. Battery positive voltage will then flow through the switch side of the starter relay to the S terminal of the starter solenoid, cranking the engine. For remote vehicle start (RVS) information, refer to Keyless Entry System Description and Operation.

Power Mode Master
This vehicles body control module (BCM) functions as the power mode master (PMM). Refer to Power Mode Description and Operation for a complete description of power mode functions.

Power to many of this vehicle's circuits are controlled by the module that is designated the power mode master (PMM). This vehicle's PMM is the body control module (BCM). The PMM controls which power mode (Run, Accessory, Crank, Retained Accessory Power, or Off) is active.
Serial Data Power Mode Master
On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle, the PMM is the body control module (BCM). The PMM receives 3 discrete ignition switch signals to differentiate which power mode will be sent over the Serial Data circuits. The 3-wire Ignition Switch table below illustrates the state of these inputs in correspondence to the ignition switch position:

Relay Controlled Power Mode
The body control module (BCM) uses the discrete ignition switch inputs Off/Run/Crank, Accessory, and ignition 1, to distinguish the correct power mode. The ignition 1 circuit is also routed to the Run/Crank relay for relay controlled power feeds during the appropriate power mode. The BCM, after determining the desired power mode, will activate the appropriate relays for that power mode.
The first step in the diagnostic procedure chart would be to hook up the Tech2 - factory scan tool an check all the modules on the vehicle for DTC'S - diagnostic trouble code's .
Your best bet have it towed to a qualified repair shop .

The ground for the relay coil is supplied by the computer(ECM). The ground for the starter is a body ground. On the relay terminals there should be two hot terminals and one ground all the tme. The coil is grounded by the computer. it will not ground if there is a security problem. The sequence starts at the ignition then goes to the security switch in the ignition or the security module, then it goes to the BCM(Body control module). Then to the ECM.Any one of theses could be bad and including the wires in between. Have the computer checked for codes, this will help out to narrow down the cause.

Looking at a wiring diagram ,the BCM has nothing to do with the cruise control . This vehicle has two different body control modules ,the (FEM) front electronic module an the (REM) rear electronic module . The power door locks are controlled by these two modules . The door lock switches are inputs to the (FEM) . The driver door lock is also controlled by the (FEM) . The right front and the rear door locks are controlled by the (REM) . The power windows are not controlled by these modules ,so it is not a faulty body computer . An where did you check codes ? Takes a factory or professional type scan tool to read these codes . No code reader , they just check PCM - engine codes . The power mirrors are not controlled by these modules either . Nor is the radio .
Looking at a wiring diagram i see the power mirror's and the power window share a common ground point G-305 , so does the rear radio controller ! (if your vehicle has one )
Buying an replacing parts is no way to fix these problems ! Using a wiring diagram and a DVOM - digital volt ohm meter to test the electrical circuits of these systems is the way to find the problem . Free wiring diagrams here http://www.bbbind.com/free_tsb.html Enter vehicle info. year , make , model and engine size . Then under system click on body an Accessorys , subsystem click power windows . Check for B+ voltage to the master window switch , check for a good ground .( Loaded circuit test ) Do you know what that means ? Watch these videos !
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