1. Instructor Name: (Your Name)
CHAPTER 13
Body Control Modules
Instructor Name: (Your Name)

2. Learning Objectives Explain the concept of virtual fusing
List the type of inputs and outputs used by a typical body control module
Discuss the reasons that most electronic control modules used in modern trucks make use of a reference ground
Discuss the difference between a conventional switch and diagnosable switch
Describe how a body control module can act as a turn signal flasher

3. Learning Objectives (continued)
Retrieve DTC’s stored in memory related to the body controller
List the main components of the International Diamond Logic® and Freightliner® Smart Plex™ multiplexed electrical systems
Describe how a Freightliner Smart Switch operates
Explain the concept of ghost voltage and describe how it can lead to confusion when diagnosing an electrical problem

4. International Multiplexed Electrical System
Referred to as the Diamond Logic electrical system
Between body control modules were referred to as electrical system controller (ESC)
In 2007 the name was changed to the body controller

5. International ESC
Figure 13-1 International electrical system controller (ESC).

6. International Body Controller
Figure 13-2 International body controller.

7. Overview of Body Controller
Figure 13-3 Overview of body controller.

8. Tech Tip
Think of the J1939 data link as both being an input and an output device for most electronic devices. The messages received by a module are inputs; the messages sent by a module are the outputs.

9. Typical Body Control Module Horn Circuit
Figure 13-5 Typical body control module horn circuit.

10. Body Controller Outputs
The body controller has three main types of outputs:
High side drivers
Low side drivers
Messages transmitted on the J1939 data link

11. High Side Driver Capable of sourcing high levels of current
The high side drivers used in body controllers are power MOSFETs (FETs)
Some FETs are capable of sourcing 20A continuously
Smart FETs can monitor the amount of current that the FET is conduction

12. Current Feedback For Virtual Fusing
Figure 13-6 The high side driver measures the current being conducted and feeds back this information to the microprocessor as a proportional voltage.

13. Low Side Drivers Current ratings of 1A or less
Commonly used in body controllers
Low side drivers sink a path to ground
Typically used to energize relay coils or small solenoids

14. Body Controller Inputs
There are three main types of inputs to the body controller:
Hardwired inputs from switches and sensors
Messages received from a proprietary switch data link
Messages received from the J1939 data link

15. Hardwired Inputs Conventional switch to control electrical devices
Reference ground is a single ground that all sensors and switches share
Reference ground is connected to chassis ground but in one location usually inside the electronic module

16. Common Reference Ground Located in Body Controller
Figure 13-7 The common reference ground point inside of body controller is connected to chassis ground at only one location.

17. CAUTION
It is vital that any electronic system that uses a reference ground only be grounded in accordance with OEM recommendations. Even though reference ground may appear to be the same as chassis ground, connecting the reference ground to chassis ground outside the electronic module may result in the truck having intermittent EMI induced problems that are nearly impossible to duplicate or troubleshoot.

18. Open and Closed Switches with Digital Input
Figure 13-8 Open switch (upper) and closed switch (lower) with digital input.

19. Open Circuit Prevents Digital Input From Detecting Switch is Closed
Figure 13-9 Open circuit prevents digital input from detecting that switch is closed; input voltage should be 0V with switch closed, but is actually +12V.

20. Diagnosable Switch With Contacts Open and Closed
Figure Diagnosable switch with contacts open and closed.

21. Diagnosable Switch Open; 8V at the Input Terminal
Figure Diagnosable switch open; 8V at input terminal.

22. Diagnosable Switch Closed; 6V at the Input Terminal
Figure Diagnosable switch closed; 6V at input terminal.

23. Diagnosable Switch Open Circuit; 12V at the Input Terminal
Figure Diagnosable switch open circuit; 12V at input terminal.

24. Switch Packs
International trucks with body controllers use switch packs using J1708/J1578 specification data link
This proprietary link is not the same as the J1708/J1587 data link connected to the power train or ECM modules
Switch packs are rockers that require switch actuators installed in them

25. Switch Pack with Switch Actuators Removed
Figure Switch pack with the switch actuators removed.

26. Tech Tip
Think of high side drivers as being like conventional relays. A small signal provided by the microprocessor is used to control a large amount of current.

27. Body Controller Headlight Circuit
Figure Body controller headlamp circuit. EGC contains headlamp switch.

28. Turn-Signal System, International Truck With Body Controller
Figure Turn-signal system on International trucks with body controller. Two switches are inputs; four high side drivers are outputs.

29. Tech Tip
The body controller only powers the applicable trailer light relay control circuit. The body controller does not directly supply the current to the trailer lighting. A conventional CPD such as a fuse or a circuit breaker in the PDC is used to protect the trailer wiring, not virtual fusing.

30. A/C System Inputs; Outputs Is A/C Clutch High Side Driver
Figure Air conditioning system inputs; output is A/C clutch high side driver.

31. Cruise Control Related Inputs Output is J1939 Message to Engine ECM
Figure Cruise control related inputs; output is J1939 message to engine ECM.

32. Primary and Secondary Air Pressure Measurement System
Figure Primary and secondary air pressure measurement system.

33. Windshield Wiper System Outputs
Figure Windshield wiper system outputs; one high side driver and two low side drivers.

34. Wiper Switch Inputs and Truth Table
Figure Wiper switch inputs and truth table.

35. Tech Tip
An open windshield wiper switch connection on an International truck with a body controller causes the wiper to operate at high speeds at any time the key switch is in the ignition position. Additionally, a short to ground of the windshield washer pump control circuit will cause the windshield wipers to operate at low speed any time the key switch is in the ignition position because the controller is falsely detecting that the washer switch is depressed.

36. Freightliner Multiplexed Electrical System
Freightliner refers to their multiplexed electrical system as SmartPlex™
The bulkhead module (BHM) acts as the primary command module for body and chassis electrical systems.
The chassis module (CHM) is the other standard electronic module
The CHM is a slave or dependent that receives commands from the BHM

37. Freightliner SmartPlexTM Electronic Module Locations
Figure Freightliner SmartPlexTM electronic module locations.

38. Bulkhead Module (BHM)
Main electronic controller for Freightliner SmartPlexTM electrical system
The BHM is connected to the J1939 data link and transmits and receives information from other electronic modules
The BHM is hardwired to several inputs in the cab
Direct hardwired high side outputs include horn, dome light, left side low-beam and high beam headlights

39. Freightliner Smart Switch Schematic
Figure Freightliner smart switch schematic.

40. Chassis Module (CHM)
Contains several high side driver FETs that source current to several chassis electrical features
The CHM is dependent on commands from the BHM via the J1939 data link
High side driver outputs include park and marker lights, back-up lamps, turn signal lamps, right side high and low beam headlights and fog lamps

41. Freightliner Multifunction Switch
Figure Freightliner multifunction switch.

42. Freightliner Multiplexed Headlamp Control
Figure Freightliner multiplexed headlamp control.

43. Troubleshooting The Multiplexed Truck
Best if performed with OEM diagnostic software and a PC, referred to as a electronic service tool (EST)
Software for Freightliner trucks is ServiceLink®
Software for International trucks is diamond Logic®
This software permits viewing diagnostic trouble codes by the body controller and EGC, along with fault descriptions

44. International Diagnostic Code Retrieval
Place the ignition switch in the ignition or accessory position
Set the park brake
Depress the cruise control ON and RESUME switches at the same time
The EGC will indicate the number of DTCs that exist

45. Diagnostic Trouble Codes Display
Figure Diagnostic trouble codes as displayed in instrument panel cluster odometer display.

46. SAE J1939 Suspect Parameter Number
Figure SAE J1939 suspect parameter number (SPN).

47. SAE J1939 Failure Mode Indicator
Figure SAE J1939 failure mode indicator.

48. ORH Condition at a Pulled-Up Input With Open Circuit
Figure ORH condition at a pulled-up input with an open circuit.

49. ORL Condition at a Pulled-Up Input with Grounded Circuit
Figure ORL condition at a pulled-up input with a ground circuit.

50. ORL Condition at a Pulled-Down Input With Open Circuit
Figure ORL condition at a pulled-down input with an open circuit.

51. Summary
The body control module on International High Performance Vehicles is called the electrical system controller (ESC) on model year trucks and the body controller on 2007 and later year trucks. The body controller or ESC contains a microprocessor. The body controller or ESC uses information obtained from input sources to control the outputs.

52. Summary(continued)
Outputs of the body controller include high side drivers, low side drivers, and messages on the J1939 data link.
Input sources for the body controller include messages from the J1939 data link, messages from the switch link, and hardwired inputs such as switches and sensors.
A reference ground scheme is commonly used in automotive electronics to minimize the effects of electromagnetic interference and to improve measurement accuracy for sensor circuits.

53. Summary(continued)
A diagnosable switch is a special switch that provides specific values of resistance, unlike a conventional switch, which is either an open circuit or a near 0Ω. A diagnosable switch is connected to an analog input. This permits circuit failures such as an open circuit or a shorted-to-ground circuit to be diagnosed.

54. Summary(continued)
The body controller controls several electrical system features, including headlamps, turn signals, stop lamps, and windshield wipers. The various switches act as inputs to the body controller through either hardwiring or multiplexing. The body controller microprocessor makes decisions based on its programming and provides an output in the form of energizing a high side driver, energizing low side driver, or transmitting a data link message.

55. Summary(continued)
Self-diagnostics assists in troubleshooting the body controller. Diagnostic trouble codes may be logged to indicate a circuit that is out of range high or out of range low.
The Freightliner SmartPlexTM system uses two or more separate modules to control body electrical features. The bulkhead module (BHM) controls the chassis module (CHM) via the J1939 data link.

56. Summary(continued)
The Freightliner SmartPlexTM uses optional smart switches to control electrical system features. Each smart switch contains two identification resistors that uniquely define the switch function.
The instrument cluster in the Freightliner SmartPlexTM system is called the ICU. The ICU acts as the input device for the stalk mounted multifunction switch. The ICU transmits the status of the multifunction switch inputs on the J1939 data link.

57. Summary(continued)
Diagnostic trouble codes (DTCs) are used to indicate that an electrical module has detected and abnormal condition. DTCs may indicate a sensor in-range operating condition, such as engine coolant temperature is too high. DTCs may also indicate sensor out of range conditions, such as open circuits or shorts to grounds. A J1939 DTC consists of an SPN and FMI.

58. Summary(continued)
Ghost voltage describes an open circuit measurement of a voltage by a DMM in a circuit with high resistance. Ghost voltage can result in misdiagnosis.