Car died while driving, cranks, but won't fire, no communication with scan tool as far as engine or transmission. It will communicate with body.

Do you know the complexity of the electronics on that vehicle, what has to happen for the PCM/ECM - engine computer to energize the starter relay, there by engaging the starter?
This is factory service repair info.

Circuit Description
When the ignition switch is placed in the Start position, a discrete 12-volt signal is supplied to the body control module (BCM) notifying it that the ignition is in the Start position. The BCM then sends a message to the engine control module (ECM) notifying it that CRANK has been requested. The ECM verifies that the transmission is in Park or Neutral. If it is, the ECM then supplies 12 volts to the control circuit of the crank relay. When this occurs, battery positive voltage is supplied through the switch side of the crank relay to the S terminal of the starter solenoid.

If the scan tool reports lost communication with BCM it won't crank or start.

Have a scan tool ? Factory or some other professional type scan tool . Not a code reader ,code reader will not view BCM - body control module codes or switch input data . Plus you would need to know how it all works . Ignition switch is a low voltage input to the BCM . Depending on switch position , ACC / RUN / START etc... the BCM will set the power mode for the vehicle by energizing relay's an sending serial data messages over the GMLAN high speed serial data network to different control modules - PCM - powertrain control module . The BCM on your vehicle is what GM calls the PMM - power mode master .

The body control system consists of the body control module (BCM), communications, and various input and outputs. Some inputs, outputs and messages require other modules to interact with the BCM. The BCM also has discrete input and output terminals to control the vehicle body functions. The BCM is wired to the GMLAN High speed serial data buss and the GMLAN Low speed serial data buss and acts as a gateway between them. If the BCM does not communicate the vehicle will not start due to the inability of the engine/powertrain control module (ECM/PCM) and vehicle theft deterrent (VTD) control module to communicate without the BCM providing the gateway function.
Power Mode Master
This vehicles BCM functions as the power mode master (PMM). The ignition switch is a low current switch with multiple discrete ignition switch signals to the PMM for determination the power mode that will be sent over the serial data circuits to the other modules that need this information, and so the PMM will activate relays and other direct outputs of the PMM as needed. Refer to Power Mode Description and Operation for a complete description of power mode functions.
Serial Data Gateway
The BCM in this vehicle functions as a gateway or translator. The purpose of the gateway is to translate serial data messages between the GMLAN high speed buss and the GMLAN low speed buss for communication between the various modules. The gateway will interact with each network according to that network's transmission protocol.
One example of this necessary communication is the communication between the engine/powertrain control module (ECM/PCM) which is high speed serial data and vehicle theft deterrent (VTD) control module which is low speed serial data. If these modules can not exchange information, the vehicle will not start.
Communication between the BCM and a scan tool can be on the high speed GMLAN network or low speed GMLAN network. If one network is lost, the BCM can still communicate with the scan tool. A lost communication DTC typically is set in modules other than the module with a communication failure.

Serial Data Power Mode Master
Power to many of this vehicles circuits is controlled by the module that is designated the power mode master (PMM). This vehicles PMM is the body control module (BCM). The ignition switch is a low current switch with multiple discrete ignition switch signals to the PMM for determination of the power mode that will be sent over the serial data circuits to the other modules that need this information. The PMM will also activate relays and other direct outputs of the PMM as needed. The PMM determines which power mode (Off, Accessory, Run, Crank Request) is required, and reports this information to other modules via serial data. Modules which have switched voltage inputs may operate in a default mode if the PMM serial data message does not match what the individual module can see from its own connections.

Circuit Description
When the ignition switch is placed in the Start position, a discrete 12-volt signal is supplied to the body control module (BCM) notifying it that the ignition is in the Start position. The BCM then sends a message to the engine control module (ECM) notifying it that CRANK has been requested. The ECM verifies that the transmission is in Park or Neutral. If it is, the ECM then supplies 12 volts to the control circuit of the crank relay. When this occurs, battery positive voltage is supplied through the switch side of the crank relay to the S terminal of the starter solenoid.

Will not spin over ? When you turn the key to start ,the starter doesn't engage an spin the engine ? Dash light's come , headlamps come on bright ? Battery good , charged ? No codes ? just engine ,OBD 2 codes ? BCM codes ? How or what did you use to check codes ? code reader , scan tool ? A professional type that can read BCM - body control module codes ? Do you have any idea how complex the electronic's are on this vehicle ? Do you know what happen's when you turn the key to start ?

Power Mode Master
This vehicle body control module (BCM) functions as the power mode master (PMM). The ignition switch is a low current switch with multiple discrete ignition switch signals to the PMM for determination the power mode that will be sent over the serial data circuits to the other modules that need this information, and so the PMM will activate relays and other direct outputs of the PMM as needed. Refer to Power Mode Description and Operation for a complete description of power mode functions.

The body control system consists of the body control module (BCM), communications, and various input and outputs. Some inputs, outputs and messages require other modules to interact with the BCM. The BCM also has discrete input and output terminals to control the vehicle's body functions. Battery positive voltage is provided to the BCM from the BCM fuse in the underhood fuse block. The module has two grounds at G 202 as well as one directly to the vehicle battery. The BCM is wired to the GMLAN High speed serial data buss and the GMLAN Low speed serial data buss and acts as a gateway between them. If the BCM does not communicate the vehicle will not start due to the inability of the engine/powertrain control module (ECM/PCM) and vehicle theft deterrent (VTD) control module to communicate without the BCM providing the gateway function.

Gateway
The body control module (BCM) in this vehicle functions as a gateway or translator. The purpose of the gateway is to translate serial data messages between the GMLAN high speed buss and the GMLAN low speed buss for communication between the various modules. The gateway will interact with each network according to that network's transmission protocol.
One example of this necessary communication is the communication between the engine/powertrain control module (ECM/PCM) which is high speed serial data and vehicle theft deterrent (VTD) control module which is low speed serial data. If these modules can not exchange information, the vehicle will not start.
All communication between the BCM and a scan tool is on the High speed GMLAN serial data circuits. A lost communication DTC typically is set in modules other than the module with a communication failure.
If you don't know of any of this ,your best bet , take it to a qualified repair shop.

Did you check for BCM codes
DTC B1477
Retained Accessory Power Circuit Low
DTC B1478
Retained Accessory Power Circuit High
DTC B1397
Device Voltage Reference Out #1 CKT Low
DTC B1398
Device Voltage Reference Out #1 CKT High
Charging system check ?

Diagnostic System Check - Retained Accessory Power
Test Description
The numbers below refer to the step numbers on the diagnostic table.

1. Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.


2. This step is checking for DTCs in the BCM.


3. This step is checking for RAP specific DTCs.

Step

Action

Yes

No

1

Install a scan tool.

Does the scan tool power up?
Go to Step 2
Go to Scan Tool Does Not Power Up in Data Link Communications

2

1. Turn ON the ignition, with the engine OFF.
2. Attempt to establish communication with the body control module.

Does the scan tool communicate with the BCM?
Go to Step 3
Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications

3

Important: The engine may start during the following step. Turn OFF the engine as soon as you have observed the Crank power mode.

1. Access the Class 2 Power Mode in the Diagnostic Circuit Check on the scan tool.
2. Rotate the ignition switch through all positions while observing the Class 2 Power Mode on the Scan Tool. Refer to the Serial Data Power Mode table within the Body Control System Description and Operation in Body Control Systems, for a list of the power mode states that correspond to each ignition switch position.

Does the Class 2 Power Mode parameter reading match the ignition switch position for all the selected positions?
Go to Step 4
Go to Power Mode Mismatch in Body Control System

4

Select the BCM display DTCs function on the scan tool.

Does the scan tool display any DTCs?
Go to Step 5
Go to the Symptoms list in the appropriate service category

5

Does the scan tool display B1477 or B1478?
Go to Diagnostic Trouble Code (DTC) List
Go to Symptoms - Retained Accessory Power

I'm just curious if your aware of the BCM function's on your vehicle an if you know what the gate way module is ? An do you know about serial data communication between modules ? An do you know what the power mode master is ? And do you know the BCM needs programming ?
The body control module (BCM) in this vehicle functions as a gateway or translator. The purpose of the gateway is to translate serial data messages between the GMLAN high speed buss and the GMLAN low speed buss for communication between the various modules. The gateway will interact with each network according to that network's transmission protocol.
One example of this necessary communication is the communication between the engine control module (ECM)/powertrain control module (PCM) which is high speed serial data and Theft Deterrent Module which is low speed serial data. If these modules can not exchange information, the vehicle will not start.
Communication between the BCM and a scan tool can be on the high speed GMLAN network or low speed GMLAN network. If one network is lost, the BCM can still communicate with the scan tool. A lost communication DTC typically is set in modules other than the module with a communication failure.

Is check engine light Lit ? You should have all the computers on the vehicle check for DTC'S - diagnostic trouble codes ! Check the battery an all connections !
Diagnostic Starting Point - Engine Electrical
Begin the system diagnosis with the Diagnostic System Check - Engine Electrical . The Diagnostic System Check will provide the following information:
?€¢
The identification of the control module(s) which command the system.

?€¢
The ability of the control modules to communicate through the serial data circuit.

?€¢
The identification of any stored diagnostic trouble codes (DTCs) and their status.

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.
Diagnostic System Check - Engine Electrical
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
The symptom list in Symptoms will determine the correct diagnostic procedure to use.
The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.
Step
Action
Yes
No

1
Did you perform the Battery Inspection/Test?
Go to Step 2
Go to Battery Inspection/Test

2
Install a scan tool.
Does the scan tool power up?
Go to Step 4
Go to Scan Tool Does Not Power Up in Data Link Communications

3
Important: The engine may start during the following step. Turn OFF the engine as soon as you have observed the Crank power mode.
Access the Class 2 Power Mode in the Diagnostic Circuit Check on the scan tool.
Rotate the ignition switch through all positions while observing the Class 2 Power Mode on the Scan Tool. Refer to the Serial Data Power Mode table within the Body Control System Description and Operation in Body Control System for a list of the power mode states that correspond to each ignition switch position.
Does the Class 2 Power Mode parameter reading match the ignition switch position for all the selected positions?
Go to Step 4
Go to Power Mode Mismatch in Body Control System

4
Turn ON the ignition, with the engine OFF.
Attempt to communicate with each module on the class 2 serial data circuit:
• The body control module (BCM)
• The driver information center (DIC)
• The instrument panel cluster (IPC)
• The powertrain control module (PCM)
Does the scan tool communicate with any module on the class 2 serial data circuit?
Go to Step 5
Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications

5
Select the Display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules have DTCs set.
Record all of the displayed DTCs the DTC status and the module which set the DTC.
Does the scan tool display any DTCs?
Go to Step 6
Go to Symptoms - Engine Electrical

6
Does the scan tool display any DTC beginning with "U"?
Go to Diagnostic Trouble Code (DTC) List in Data Link Communications
Go to Step 7

7
Does the scan tool display any DTC beginning with "B"?
Go to Diagnostic Trouble Code (DTC) List in Body Control Systems
Go to Diagnostic Trouble Code (DTC)

This is what would be done at the dealer or any good repair shop !
Perform the following preliminary inspections:
?€¢
Ensure that the battery is fully charged. Refer to Battery Inspection/Test .

?€¢
Ensure that the battery cables are clean and tight.

?€¢
Inspect for any open fuses.

Refer to Power Distribution Schematics and Electrical Center Identification Views .

?€¢
Inspect the easily accessible systems or the visible system components for obvious damage or conditions that could cause the symptom.

?€¢
Ensure that the grounds are clean, tight, and in the correct location.

Refer to Ground Distribution Schematics and Power and Grounding Component Views .

?€¢
Inspect for aftermarket devices that could affect the operation of the system. Refer to Checking Aftermarket Accessories .

?€¢
Search for applicable service bulletins.

Did you find and correct the condition?
System OK
Go to Step 2

2

Install a scan tool.
Does the scan tool power up?
Go to Step 3
Go to Scan Tool Does Not Power Up

3

1. Turn ON the ignition, with the engine OFF.
2. Attempt to establish communication with all of the control modules on the vehicle. Refer to Scan Tool Does Not Communicate with Class 2 Device for the modules you should expect to observe.

Does the scan tool communicate with all of the expected vehicle control modules
Important:
?€¢
To ensure that retained accessory power (RAP) mode is inactive, if equipped, open the drivers door during the following step.

?€¢
The engine may start during the following step. Turn OFF the engine as soon as you have observed the crank power mode.

1. Access the Power Mode parameter on the scan tool.
2. Rotate the ignition switch, operate the ignition mode switch, through all positions while observing the Power Mode parameter. Refer to Body Control System Description and Operation for a list of the power mode states that correspond with each switch position.

Does the Power Mode parameter reading on the scan tool match the ignition switch position for all switch positions?
Go to Step 5
Go to Power Mode Mismatch

5

Attempt to start the engine.
Does the engine crank?
Go to Step 6
Go to Symptoms - Engine Electrical

2

Turn the ignition to the START position.
Does the engine crank?
Go to Testing for Intermittent Conditions and Poor Connections
Go to Step 3

3

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Verify that the transmission is in Park or Neutral.
4. With a scan tool, observe the IMS parameter in the powertrain control module (PCM)/engine control module (ECM) data list.

Does the scan tool display Park or Neutral?
Go to Step 4
Go to Range Selector Displays Incorrect Range

4

1. Turn ON the ignition, with the engine OFF.
2. With a scan tool, observe the Starter Relay Command parameter in the PCM/ECM data list.
3. Turn the ignition to the START position.

Does the scan tool display Yes?
Go to Step 6
Go to Step 5
With all the modules on your vehicle you really need to start with a professional grade scan tool to see if all are communicating .

This is the way you start diagnosing this system !
Automatic Level Control Diagnostic System Check
Install a scan tool. Does the scan tool power up?
Go to Step 2
Go to Scan Tool Does Not Power Up in Data Link Communications

2

1. Turn ON the ignition, with the engine OFF.
2. Attempt to establish communication with the Rear Integrated Module (RIM).

Does the scan tool communicate with the RIM?
Go to Step 3
Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications
Select the automatic level control display DTC function on the scan tool.
Does the scan tool display any DTCs?
Go to Step 4
Go to Symptoms

4
Does the scan tool display any DTCs which begin with a "U"?
Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Connector Diagnosis
Go to Step 5

5

Does the scan tool display DTC B1007 or B1009?
Go to Diagnostic Trouble Code (DTC) List/Type in Body Control System
Go to Step 6

6

Does the scan tool display DTC B1327?
Go to Diagnostic Trouble Code (DTC) List/Type in Engine Electrical
Go to Diagnostic Trouble Code (DTC) List/Type
This is one you should take to a ASE certified repair facility , there are electronic modules involved you have no idea about !

The automatic transmission shift lock control system is a safety device that prevents an inadvertent shift out of PARK when the engine is running. The driver must press the brake pedal before moving the shift lever out of the PARK position. The system consists of the following components.
• The automatic transmission shift lock control solenoid
• The brake switch
• The rear integration module (RIM)
• The transmission control module (TCM) or powertrain control module (PCM)
With the ignition ON, battery positive voltage is supplied to the automatic transmission shift lock control solenoid from the ignition 3 relay. The automatic transmission shift lock control solenoid is controlled by the rear integration module. When the rear integration module (RIM) receives a class 2 serial data message from the transmission control module (TCM) or powertrain control module (PCM) indicating that the shift lever is in the PARK position the rear integration module (RIM) grounds the automatic transmission shift lock control solenoid control circuit. This causes the solenoid to energize mechanically locking the shift lever in the PARK position. When the driver presses the brake pedal the rear integration module receives the brake applied signal and turns off the ground to the automatic transmission shift lock control solenoid control circuit. This allows the shift lever to be moved out of the PARK position.

Step
Action
Yes
No
1
Install a scan tool.
Does the scan tool power up?
YES - Go to Step 2
NO - Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications
2
Turn ON the ignition, with the engine OFF.
Attempt to establish communication with the Powertrain Control Module (PCM) and the Rear Integration Module (RIM).
Does the scan tool communicate with the PCM and the RIM?
YES - Go to Step 3
NO - Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications
3
Important: The engine may start during the following step. Turn OFF the engine as soon as you have observed the Crank power mode.
Access the Ignition Switch parameter in the rear integration module (RIM) inputs data display list.
Rotate the ignition switch through all positions while observing the ignition switch power mode parameter.
Does the ignition switch parameter reading match the ignition switch position for all switch positions?
YES - Go to Step 4
NO - Go to Power Mode Mismatch in Body Control System
4
Select the display DTCs function on the scan tool for the PCM and the RIM.
Does the scan tool display any DTCs for the PCM or the RIM?
YES - Go to Step 5
NO - Go to Symptoms - Automatic Transmission Shift Lock Control
5
Does the scan tool display any DTCs which begin with a "U"?
YES - Go to Diagnostic Trouble Code (DTC) List in Data Link Communications
NO - Go to Step 6
6
Does the scan tool display DTC B1000, B1004, B1007, or B1009?
YES - Go to Diagnostic Trouble Code (DTC) List in Body Control System
No - Go to Step 7
7
Does the scan tool display DTC B1327?
YES - Go to Diagnostic Trouble Code (DTC) List in Engine Electrical
NO - Go to Symptoms - Automatic Transmission Shift Lock Control

This is something best left to the Cadillac dealer !

do you have ignition fire? does the check engine/service engine soon light come on when when you turn the key on? can a scan tool communicate with the ECM? there are several things to check if you have no power to the fuel pump because the fuel pump relay is controlled by the ECM.