Electronic Control Modules: Overview Dodge Caravan IV

DESCRIPTION

The Body Control Module (BCM) is located in the passenger compartment, attached to the bulkhead underneath the left side of the instrument panel.

The BCM utilizes integrated circuitry and information carried on the Programmable Communications Interface (PCI) data bus network along with many hard wired inputs to monitor many sensor and switch inputs throughout the vehicle. In response to those inputs, the internal circuitry and programming of the BCM allow it to control and integrate many electronic functions and features of the vehicle through both hard wired outputs and the transmission of electronic message outputs to other electronic modules in the vehicle over the PCI data bus.

OPERATION

The Body Control Module (BCM) supplies vehicle occupants with visual and audible information and controls various vehicle functions. To provide and receive information, the BCM is interfaced to the vehicle's serial bus communications network, referred to as the Programmable Communications Interface (PCI) bus.

This network consists of the

1. Powertrain Control Module (PCM)
2. Transmission Control Module (TCM)
3. Mechanical Instrument Cluster (MIC)
4. Occupant Restraint Controller (ORC)
5. Compass/Mini-Trip Computer (CMTC)
6. Electronic Vehicle Information Center (EVIC)
7. Controller Antilock Brake (CAB)
8. HVAC Control Module
9. Sliding Door Control Modules (driver and passenger side doors)
10. Power Liftgate Module (PLG)
11. Audio system equipped with RAZ, RBU, RBK, and RBB radios.
12. Sentry Key Remote Entry Module (SKREEM).
13. Side Impact Airbag Control Module (SIACM)
14. Memory Seat Module (MSM)
15. Sentry Key Immobilizer Module (SKIM)

The BCM is operational when battery power is supplied to the module.

The BCM provides the following features

1. Power Door Locks
2. Automatic Door Locks
3. Battery Protection - The BCM will automatically turn off all exterior lamps after 3 minutes, and all interior lamps after 15 minutes after the ignition is turned off, if they are not turned off by the driver.
4. Chime Control
5. Compass/Mini-Trip support.
6. Interior Lighting (Courtesy/Reading Lamps)
7. BCM Diagnostic Reporting
8. Electronic Liftgate Release (with Power Door Locks)
9. Exterior Lighting
10. Headlamp Time Delay (with/without Automatic Headlamps)
11. Illuminated Entry
12. Fade to Off Interior Lamps - This feature dims the interior lighting (courtesy lamps) gradually if the BCM does not receive any new inputs that would cause the interior lamps to remain on.
13. Pulse Width Modulated Instrument Panel Dimming
14. Door Lock Inhibit - This feature disables the door lock functions if the key is in the ignition and either front door is ajar. Pressing the Remote Keyless Entry (RKE) lock/unlock button under these conditions result in normal lock/unlock activation.

The BCM has the ability to LEARN additional features in the vehicle, provided the appropriate switch input and PCI data bus messages are received. Refer to LEARNED FEATURES .

LEARNED FEATURES

When replacing a BCM there are three modules available

1. Base
2. Midline
3. RG - Export

The Midline controller is used on vehicles that have Power Door Locks. If a vehicle is equipped with the Vehicle Theft Security System, the Midline controller becomes a Premium when the theft feature is enabled.

The BCM has internal diagnostic capability that assists in diagnosing the system error. When an OPEN or a SHORT circuit exists, the diagnostic tool can be used to read the BCM faults. The faults are very descriptive in identifying the appropriate feature that has faulted.

The only two faults that the BCM logs that conclude the replacement of a BCM are faults

1. # 01 - Internal BCM failure (replace BCM)
2. # 1F - J1850 Internal Hardware Failure (replace BCM)

Otherwise the appropriate diagnostic procedures for each of the features should be taken when the BCM logs a fault.

The Antilock Brake Module (ABM) is a microprocessor-based device which monitors the antilock brake system (ABS) during normal braking and controls it when the vehicle is in an ABS stop or when in a traction control situation. The ABM utilizes a 47-way electrical connector on the vehicle wiring harness. The power source for the ABM is through the ignition switch in the RUN or ON position.

The ABM is mounted to the HCU as part of the Integrated Control Unit (ICU). (Scheme 1) The ICU is located in the engine compartment below the master cylinder on the front suspension cradle/crossmember. For information on the ICU, (Refer to BRAKES/HYDRAULIC/MECHANICAL/ICU (INTEGRATED CONTROL UNIT) - DESCRIPTION ).

Scheme 1

The primary functions of the Antilock Brake Module (ABM) are to

1. Monitor the antilock brake system for proper operation.
2. Detect wheel locking or wheel slipping tendencies by monitoring the speed of all four wheels of the vehicle.
3. Control fluid modulation to the wheel brakes while the system is in an ABS mode.
4. Store diagnostic information.
5. Provide communication to the scan tool while in diagnostic mode.
6. Illuminate the amber ABS warning indicator lamp.
7. (With traction control only) Illuminate the TRAC ON lamp in the message center on the instrument panel when a traction control event occurs.
8. (with traction control only) Illuminate the TRAC OFF lamp when the amber ABS warning indicator lamp illuminates.

The ABM constantly monitors the antilock brake system for proper operation. If the ABM detects a fault, it will turn on the amber ABS warning indicator lamp and disable the antilock braking system. The normal base braking system will remain operational.

Note. If the vehicle is equipped with traction control, the TRAC OFF lamp will illuminate anytime the amber ABS warning indicator lamp illuminates.

The ABM continuously monitors the speed of each wheel through the signals generated by the wheel speed sensors to determine if any wheel is beginning to lock. When a wheel locking tendency is detected, the ABM commands the ABM command coils to actuate. The coils then open and close the valves in the HCU that modulate brake fluid pressure in some or all of the hydraulic circuits. The ABM continues to control pressure in individual hydraulic circuits until a locking tendency is no longer present.

The ABM contains a self-diagnostic program that monitors the antilock brake system for system faults. When a fault is detected, the amber ABS warning indicator lamp is turned on and the fault diagnostic trouble code (DTC) is then stored in a diagnostic program memory. A latched fault will disable certain system functionality for the current ignition cycle. An unlatched fault will disable certain system functionality until the fault condition disappears. These DTC's will remain in the ABM memory even after the ignition has been turned off. The DTC's can be read and cleared from the ABM memory by a technician using a scan tool. If not cleared with a scan tool, the fault occurrence and DTC will be automatically cleared from the ABM memory after the identical fault has not been seen during the next 3,500 miles. Drive-off may be required for the amber ABS warning indicator lamp to go out on the next ignition cycle.

The controller antilock brake (CAB) is a microprocessor-based device which monitors the antilock brake system (ABS) during normal braking and controls it when the vehicle is in an ABS stop. The CAB is mounted to the HCU as part of the integrated control unit (ICU). (Scheme 2) The CAB uses a 24-way electrical connector on the vehicle wiring harness. The power source for the CAB is through the ignition switch in the RUN or ON position. The CAB is on the PCI bus.

Scheme 2

The primary functions of the controller antilock brake (CAB) are to

1. Monitor the antilock brake system for proper operation.
2. Detect wheel locking or wheel slipping tendencies by monitoring the speed of all four wheels of the vehicle.
3. Control fluid modulation to the wheel brakes while the system is in an ABS mode.
4. Store diagnostic information.
5. Provide communication to the DRBIII(R) scan tool while in diagnostic mode.
6. Illuminate the amber ABS warning indicator lamp.
7. (With traction control only) Illuminate the TRAC ON lamp in the message center on the instrument panel when a traction control event occurs.
8. (with traction control only) Illuminate the TRAC OFF lamp when the amber ABS warning indicator lamp illuminates.

The CAB constantly monitors the antilock brake system for proper operation. If the CAB detects a fault, it will turn on the amber ABS warning indicator lamp and disable the antilock braking system. The normal base braking system will remain operational.

Note. If the vehicle is equipped with traction control, the TRAC OFF lamp will illuminate anytime the amber ABS warning indicator lamp illuminates.

The CAB continuously monitors the speed of each wheel through the signals generated by the wheel speed sensors to determine if any wheel is beginning to lock. When a wheel locking tendency is detected, the CAB commands the CAB command coils to actuate. The coils then open and close the valves in the HCU that modulate brake fluid pressure in some or all of the hydraulic circuits. The CAB continues to control pressure in individual hydraulic circuits until a locking tendency is no longer present.

The CAB contains a self-diagnostic program that monitors the antilock brake system for system faults. When a fault is detected, the amber ABS warning indicator lamp is turned on and the fault diagnostic trouble code (DTC) is then stored in a diagnostic program memory. A latched fault will disable certain system functionality for the current ignition cycle. An unlatched fault will disable certain system functionality until the fault condition disappears. These DTC's will remain in the CAB memory even after the ignition has been turned off. The DTC's can be read and cleared from the CAB memory by a technician using the DRBIII(R) scan tool. If not cleared with a DRBIII(R) scan tool, the fault occurrence and DTC will be automatically cleared from the CAB memory after the identical fault has not been seen during the next 3,500 miles. Drive-off may be required for the amber ABS warning indicator lamp to go out on the next ignition cycle.

The data link connector is located inside the vehicle, below instrument panel next to the center column. (Scheme 3)

Scheme 3

The data link connector (diagnostic connector) links the DRB scan tool with the Powertrain Control Module (PCM). Refer to BODY DIAGNOSTIC PROCEDURES .

The Front Control Module (FCM) is a micro controller based module located in the engine compartment. The FCM mates to the Power Distribution Center (PDC) to form the Integrated Power Module (IPM). The IPM connects directly to the battery and provides the primary means of circuit protection and power distribution for all vehicle electrical systems. The FCM controls power to some of these vehicle systems electrical and electromechanical loads based on inputs received from hard wired switch inputs and data received on the Programmable Communications Interface (PCI) data bus.

For information on the IPM, (Refer to ELECTRICAL/POWER DISTRIBUTION/INTEGRATED POWER MODULE - DESCRIPTION)

As messages are sent over the Programmable Communications Interface (PCI) data bus, the Front Control Module (FCM) reads these messages and controls power to some of the vehicles electrical systems by completing the circuit to ground (low side driver) or completing the circuit to 12 volt power (high side driver).

The following functions are controlled by the Front Control Module

1. Accessory Relay Actuation
2. Brake Transmission Shift Interlock Functions (BTSI - gas engine only)
3. Diesel Cabin Heater (Diesel Engine Vehicles)
4. Electronic Back Light (EBL) Rear Defogger
5. Front and Rear Blower Motor Relay Actuation
6. Front Fog Lamp Relay Actuation
7. Washer Motor (front and rear)
8. Front Windshield Wiper "HI" & "LO" Relay Actuation
9. Front Windshield Wiper "ON" Relay Actuation
10. Headlamp Power with Voltage Regulation
11. Horn Relay Actuation
12. Headlamp Washer Relay Actuation (IF EQUIPPED - EXPORT ONLY)
13. Name Brand Speaker (NBS) Relay Actuation
14. Park Lamp Relay Actuation

The following inputs are Received/Monitored by the Front Control Module

1. Ambient Temperature Sensing
2. Back-Up switch
3. Brake Fluid Level
4. B+ Connection Detection
5. Engine Crank Signal (Diesel Engine Vehicles)
6. Horn Input
7. Ignition Switch Start Only
8. Ignition Switch Run and Start Only
9. Stop Lamp Sense
10. Washer Fluid Level
11. Windshield Wiper Park

Vehicles equipped with heated seats utilize two heated seat modules. The heated seat modules are located under the front seats, where they are secured to the seat cushion pans. Each heated seat module has three connector receptacles that allow the modules to be connected to all of the required inputs and outputs through the seat wire harness.

The heated seat modules are an electronic microprocessor controlled device designed and programmed to use inputs from the ignition switch, heated seat switch and the heated seat sensor to operate and control the heated seat elements in the front seat.

The heated seat module operates on fused battery current received from the Integrated Power Module (IPM). The module is grounded at all times through the seat wire harness. Inputs to the module include a resistor multiplexed heated seat switch request circuit for the heated seat switch and the heated seat sensor inputs from the seat cushions of each front seat. In response to those inputs the heated seat module controls battery current feeds to the heated seat elements.

When a heated seat switch request signal is received by the heated seat module and the enable input is high, the heated seat module energizes the selected heated seat sensor circuit and the sensor provides the module with an input indicating the surface temperature of the selected seat cushion.

The Low heat set point is approximately 36° C (95° F), and the High heat set point is approximately 40° C (104° F). If the seat cushion surface temperature input is below the temperature set point for the selected temperature setting, the heated seat module energizes an N-channel Field Effect Transistor (N-FET) within the module which energizes the heated seat elements in the selected seat cushion and back. When the sensor input to the module indicates the correct temperature set point has been achieved, the module de-energizes the N-FET which de-energizes the heated seat elements. The heated seat module will continue to cycle the N-FET as needed to maintain the selected temperature set point.

Vehicles equipped with the memory seat/mirror option, utilize a memory module located under the drivers front seat. This module is basically wired in-line between the power seat switch and the power seat track/adjuster motors, or in-line between the power mirror switch and the power side view mirror(s) motor(s). The Memory Seat/Mirror Module (MSMM) contains a central processing unit that communicates with other modules on the Programmable Communications Interface (PCI) data bus network.

The MSMM receives hard wired inputs from the driver power seat switch and the potentiometers on each of the driver side power seat track motors, or from the power mirror switch and the potentiometers on the side view mirror. The MSMM receives messages over the PCI data bus from the Body Control Module (BCM) (memory switch status), the Powertrain Control Module (PCM) (vehicle speed status). The MSMM will prevent the seat memory recall function from being initiated if the driver side seat belt is buckled, if the transmission gear selector lever is not in the Park or Neutral positions, or if the vehicle is moving.

For diagnosis of the MSMM or the PCI data bus, a DRB III(R) scan tool and BODY DIAGNOSTIC PROCEDURES are recommended. The MSMM cannot be repaired and, if faulty or damaged, it must be replaced.

When memory system operation is requested (depressing of the memory switch), a resistor multi-plexed signal is sent from the memory switch to the Body Control Module (BCM). The BCM will then send the appropriate signals out to the Memory Seat/Mirror Module (MSMM), the MSMM then applies the voltage supply to the power seat track or side-view mirror if the proper requirements are met. The vehicle speed must equal zero and the transmission must be in park or neutral in order for the memory system to function.

The power liftgate control module contains the electronic circuitry and software used to control the sequence of events for the power liftgate system. This module communicates on the Programmable Communications Interface (PCI) bus circuit with the vehicles Body Control Module (BCM) to monitor many different inputs and outputs such as door lock status, transmission gear selector position and vehicle speed. (Refer to ELECTRICAL/POWER DOORS - OPERATION) or (Refer to ELECTRICAL/POWER DOORS - OPERATION) for more information.

The Powertrain Control Module (PCM) is a digital computer containing a microprocessor. (Scheme 4) The PCM receives input signals from various switches and sensors referred to as Powertrain Control Module Inputs. Based on these inputs, the PCM adjusts various engine and vehicle operations through devices referred to as Powertrain Control Module Outputs.

Scheme 4

Note. PCM Inputs

1. Air Conditioning Pressure Transducer
2. Ambient temperature Sensor
3. ASD Relay
4. Battery Temperature Sensor (NGC)
5. Battery Voltage
6. Brake Switch
7. Camshaft Position Sensor
8. Crankshaft Position Sensor
9. Distance Sensor (from transmission control module)
10. EGR Position Feedback
11. Engine Coolant Temperature Sensor
12. Heated Oxygen Sensors
13. Ignition sense
14. Intake Air Temperature Sensor
15. Knock Sensor
16. Leak Detection Pump Feedback
17. Manifold Absolute Pressure (MAP) Sensor
18. Park/Neutral
19. PCI Bus
20. Power Steering Pressure Switch
21. Proportional Purge Sense
22. SCI Receive
23. Speed Control
24. Throttle Position Sensor
25. Transmission Control Relay (Switched B+)
26. Transmission Pressure Switches
27. Transmission Temperature Sensor
28. Transmission Input Shaft Speed Sensor
29. Transmission Output Shaft Speed Sensor
30. Transaxle Gear Engagement
31. Vehicle Speed

Note. PCM Outputs

1. Air Conditioning Clutch Relay
2. Automatic Shut Down (ASD) and Fuel Pump Relays
3. Data Link Connector (PCI and SCI Transmit)
4. Double Start Override
5. EGR Solenoid
6. Fuel Injectors
7. Generator Field
8. High Speed Fan Relay
9. Idle Air Control Motor
10. Ignition Coils
11. Leak Detection Pump
12. Low Speed Fan Relay
13. MTV Actuator
14. Proportional Purge Solenoid
15. SRV Valve
16. Speed Control Relay
17. Speed Control Vent Relay
18. Speed Control Vacuum Relay
19. 8 Volt Output
20. 5 Volt Output
21. Torque Reduction Request
22. Transmission Control Relay
23. Transmission Solenoids
24. Vehicle Speed

Based on inputs it receives, the powertrain control module (PCM) adjusts fuel injector pulse width, idle speed, ignition timing, and canister purge operation. The PCM regulates the cooling fans, air conditioning and speed control systems. The PCM changes generator charge rate by adjusting the generator field.

The PCM adjusts injector pulse width (air-fuel ratio) based on the following inputs.

1. Battery Voltage
2. Intake Air Temperature Sensor
3. Engine Coolant Temperature
4. Engine Speed (crankshaft position sensor)
5. Exhaust Gas Oxygen Content (heated oxygen sensors)
6. Manifold Absolute Pressure
7. Throttle Position

The PCM adjusts engine idle speed through the idle air control motor based on the following inputs.

1. Brake Switch
2. Engine Coolant Temperature
3. Engine Speed (crankshaft position sensor)
4. Park/Neutral
5. Transaxle Gear Engagement
6. Throttle Position
7. Vehicle Speed

The PCM adjusts ignition timing based on the following inputs.

1. Intake Air Temperature
2. Engine Coolant Temperature
3. Engine Speed (crankshaft position sensor)
4. Knock Sensor
5. Manifold Absolute Pressure
6. Park/Neutral
7. Transaxle Gear Engagement
8. Throttle Position

The automatic shut down (ASD) and fuel pump relays are mounted externally, but turned on and off by the powertrain control module through the same circuit.

The camshaft and crankshaft signals are sent to the powertrain control module. If the PCM does not receive both signals within approximately one second of engine cranking, it deactivates the ASD and fuel pump relays. When these relays are deactivated, power is shut off to the fuel injectors, ignition coils, fuel pump and the heating element in each oxygen sensor.

The PCM contains a voltage converter that changes battery voltage to a regulated 8.0 volts. The 8.0 volts power the camshaft position sensor, crankshaft position sensor and vehicle speed sensor. The PCM also provides a 5.0 volts supply for the engine coolant temperature sensor, intake air temperature sensor, manifold absolute pressure sensor and throttle position sensor.

The PCM engine control strategy prevents reduced idle speeds until after the engine operates for 320 km (200 miles). If the PCM is replaced after 320 km (200 miles) of usage, update the mileage in new PCM. Use the DRBIII(R) scan tool to change the mileage in the PCM. Refer to POWERTRAIN DIAGNOSTIC PROCEDURES and the DRBIII(R) scan tool.

OPERATION - SENSOR RETURN - PCM INPUT

The sensor return circuit provides a low electrical noise ground reference for all of the systems sensors. The sensor return circuit connects to internal ground circuits within the Powertrain Control Module (PCM).

OPERATION - IGNITION SENSE - PCM INPUT

The ignition sense input informs the Powertrain Control Module (PCM) that the ignition switch is in the crank or run position.

The power sliding door control module serves as the main computer for the power sliding door system. All power door functions are processed through the power sliding door control module and/or the vehicles Body Control Module (BCM). At the start of a power open command, a signal is sent to the BCM and then to the power sliding door control module via the Programmable Communication Interface (PCI) data bus circuit. This signal, generated by any of the power door command switches, tells the power sliding door control module to activate a power latch release, engage the clutch assembly and drive the door into the full open position. If an obstacle is felt during this power open cycle, the module will reverse direction and close the door. This process is also enabled during a power close cycle. This process will repeat three times, and if a fourth obstacle is detected, the door will go into full manual mode. Once the full open position is obtained, a hold open latch assembly mounted full open switch tells the power sliding door control module that the door has reached the full open position. If the power sliding door system develops any problems the power sliding door control module will store and recall Diagnostic Trouble Codes (DTC). The use of a diagnostic scan tool, such as the DRB III(R) is required to read and troubleshoot these trouble codes.

See also:
• BODY DIAGNOSTIC PROCEDURES
• POWERTRAIN DIAGNOSTIC PROCEDURES