Notes

Automotive Control Modules
An automotive control module controls one or more electrical subsystems in a vehicle. They are solid state controllers that combine integrated circuits and other devices into a single assembly. Control modules are located throughout a vehicle. Select each button to learn more. When finished, select Next to continue.

Body Control Module The Body Control Module (BCM) controls many functions throughout the vehicle, such as interior and exterior lighting.

Brake System Control Module The brake system control module controls antilock brakes and the brake assist system.

Inflatable Restraint Sensing and Diagnostic Module
The inflatable restraint sensing and diagnostic module controls the supplemental inflatable restraint systems.

Engine Control Module The Engine Control Module (ECM) controls functions within the engine and transmission.

Control Module Circuitry
Automotive control modules perform a variety of tasks. These tasks include receiving input signals, performing calculations, sending output signals based on the calculations and input signals, and storing information.

Automotive Control Module Characteristics
While it is true that there are many different types of control modules, there are some characteristics that are common in all control modules. Those common characteristics are listed here. Select each button to learn more. When finished, select Next to continue.

Input Interface
The input interface receives signals from input sensors and converts them into digital signals that the central processing unit can understand.

Central Processing Unit The central processing unit is the most important element of a control module. The central processing unit receives input data, processes the data, and creates an output based on internal programming.

Output Interface
The output interface takes data from the central processing unit and converts it into a format that can be used by other computers or actuators.

Central Processing Unit
The central processing unit, also known as the microprocessor, receives data from sensors, performs calculations, and responds according to programming. The central processing unit also sends out electrical signals to actuators and controllers based on results of the calculations and programming.

Integrated Circuit An integrated circuit, contained within the central processing unit, is a complete electronic circuit that can integrate many transistors, diodes, and resistors on a small chip of silicon. Because of their low cost, small size, and reliability, integrated circuits are widely used in

Types of Integrated Circuits
Integrated circuits may be classified as two types: analog or digital. A digital circuit is also known as a switching circuit, and an analog circuit is also known as a linear circuit. Both digital and analog circuits serve to process the data received and send an output. Digital and analog circuits combine with traditional components—such as transistors, resistors, and capacitors—to create control modules. Select each button to learn more. When finished, select Next to continue.

Digital
Digital circuits are used to process and store information. Digital circuits add numbers, convert numbers from decimal code to binary code, transmit data, and store data.

Analog
Analog circuits are used to amplify, or increase, the power, current, or voltage received as inputs.

Memory Types The control module stores data and programming in integrated circuit memory chips. There are three types of memory: Read Only Memory (ROM), Random Access Memory (RAM), and Programmable Read-Only Memory. Select each button to learn more. When finished, select Next to continue.

Read Only Memory
Read Only Memory (ROM) memory stores the most basic operating instructions of the computer. Without ROM, a computer will not start. ROM is permanent, or non-volatile. That is, the data on a ROM memory chip is not erased when power is removed or a module is unplugged.

Random Access Memory
Random Access Memory (RAM) allows the central processing unit to store temporary data and recall it when required. This data typically is used for diagnostic purposes and can be overwritten as needed

Programmable Read-Only Memory
Programmable read-only memory is a memory chip inside the computer that can be electronically erased and rewritten when software needs to be changed. This memory chip is sometimes referred to as the E-PROM

Programmable Read-Only Memory
Most control modules will require programming of the programmable read-only memory if the control module is replaced. A scan tool is used to program the programmable read-only memory.

Control Module Monitor
A control module monitors changes in voltage levels of the input. An input is a signal sent to the control module that is used for making calculations and may result in an output signal or command. For example, when one door is open the Body Control Module (BCM) receives an input indicating that a door is open. This input is processed by the central processing unit, and as a result the BCM sends a signal, or output, that illuminates the dome light.

Switched Input
A switched input is the simplest kind of signal the control module receives. The input from this sensor is a high or low signal, depending on whether the switch is open or closed.

Pull-Up Circuit
A pull-up circuit has a power source outside of the control module. When a switch is closed on this circuit, external source voltage generates a high reference signal to the control module. An open switch, on the other hand, generates a low frequency reference signal to the control module.

Pull-Down Circuit
A pull-down circuit has a power source internal to the control module. When the switch is closed, signal voltage is pulled down to an external ground. The control module registers a low voltage reference signal. When the switch is open, the control module registers a high frequency reference signal.

Control Module
The control module receives two types of inputs: analog and digital. Because a control module only understands digital (binary) input, all analog voltage signals must be converted to digital (binary) code. Select each button to learn more. When finished, select Next to continue.

Analog Inputs
Analog inputs are depicted as curved waves, as in this measurement of a throttle position sensor. The signal is continuous between the lowest reading of 0 volts and the highest value of 5 volts. At one-half throttle, voltage is 2.5 volts. This data is converted to a binary reading of 'acceptable' or 'not acceptable' for the control module.

Digital Inputs
Digital inputs are represented as square waves, where the low measurement is 0 and the high is a positive voltage. The control module would assign a 0 value to the lower measurement and define the high value as 1.

Control Module Outputs
A control module uses high side and low side drivers to send outputs using several methods. These methods include applying voltage, applying ground, or alternately applying voltage and ground. Select each button to learn more. When finished, select Next to continue.

High Side Driver
A high side driver applies voltage as an output of the control module. Applying voltage to the circuit allows the circuit to operate. Positive-Negative-Positive transistors are used for high side drivers within control modules.

Low Side Driver
A low side driver supplies ground as an output of the control module. Supplying ground to the circuit allows the circuit to operate. Negative-Positive-Negative transistors are used for low side drivers within control modules.

High Side Driver Example Consider this example of a high side driver. Under certain circumstances, such as when the control module receives an input indicating a wheel lockup, the Electronic Brake Control Module (EBCM) will close one of its internal switches. This applies battery voltage to an Antilock Braking System (ABS) solenoid and the solenoid is actuated, reducing wheel skid and allowing the driver to maintain control of the vehicle. In this example, the control module is applying voltage as an output signal because the voltage is either on or off.

Low Side Driver Example
Consider this example of a low side driver: Normally, the switch inside the EBCM is open, and the brake indicator circuit is not grounded. Under certain circumstances, if a fault in the ABS system is present, the EBCM closes the switch and applies ground to the circuit. The majority of control module systems use this method for grounding a device.

Digital Signal
A digital signal has only two possible values, which are usually called “on” and “off.” When the signal is off, the actuator doesn’t operate. When the signal is on, the actuator does operate. If the signal fluctuates quickly between on and off, the actuator runs at a speed between on and off. This is called Pulse Width Modulation (PWM). PWM is used in many applications, such as a fuel injector.

Pulse Width Modulation Digital Signal
All PWM signals are digital. Each digital signal is shown over time. Total time is divided into time periods of equal lengths. During each period, the signal is on for a certain percentage of the total time. The ratio of on time to total time is called the duty cycle. The higher the duty cycle percentage, the longer the component operates.