2005 GENERAL INFORMATION Electronic Signals - Overview (2024)

Electronic Signals

Model: All

Production Date: All

Purpose of Signals

Electronic signals move information much like cars move passengers down the highway. It would be difficult to get to work without transportation, and there would be no transportation with out signals.

Signals allow devices (e.g. sensors or switches) to communicate with control modules (either complicated processors or simple relays) which in turn perform or request (through more signaling) other functions to be carried out.

Signals inform the Climate Control of the outside air temp or tell the brake lights the right time to illuminate.

The use of electronic signals goes far beyond the basic application of electron flow to control components, enabling complex information to be passed from one component to another.

The data (input or output) is conveyed through various forms of changing voltages, resistances, current or frequency modulation.

1. AC Voltage Signals:
   1. Inductive Signals.
   2. Phase Shifted Signals.

   Fig. 1: Identifying AC Voltage Signals
   Courtesy of BMW OF NORTH AMERICA, INC.

2. DC Voltage Signals:
   1. Analog Signals.
   2. Digital Signals:
      1. Switched (High/Low) Signals.
      2. Modulated Square Wave Signals:
         1. Frequency Controlled Signals.
         2. Pulse Width Controlled Signals.
         3. Duty Cycle Controlled Signals.
   3. Designated Value Signals.
   4. Coded Ground Signals.
   5. Transistor Signals:
      1. Modulated B+/B- Signals.
      2. Momentary B+/B- Signals.
      3. Constant B+/B- Signals.

         Fig. 2: Identifying DC Voltage Signals
         Courtesy of BMW OF NORTH AMERICA, INC.

AC Voltage Signals

Two types of AC Voltage signals are used:

• Inductive Signals (Induced Voltage).
• Phase Shifted Signals (Angle Pulse Generator).

Inductive Sensors

Inductive sensors produce an AC Sine Wave signal. The AC voltage is induced by the shifting of a magnetic field. The sensor consists of an impulse wheel (the moving part) and a coil wound magnetic core (the stationary part).

As each tooth of the impulse wheel approaches the sensor tip, the magnetic field of the sensor shifts toward the impulse wheel and induces a voltage pulse in the windings.

As the teeth move away from the sensor, the magnetic field shifts back inducing a voltage pulse in the opposite direction.

This shifting of the magnetic field produces an alternating current (positive to negative).

Control modules which receive this alternating current, count the impulses (shifts from positive to negative) and interpret the speed of rotation of the impulse wheel.

Fig. 3: Inductive Sensor Circuit Diagram
Courtesy of BMW OF NORTH AMERICA, INC.

Typical Application of Inductive Sensors:

• Crankshaft Speed Sensor.
• Camshaft Speed Sensor.
• Transmission Input/Output Speed Sensor.
• Wheel Speed Sensor.

Fig. 4: Identifying AC Sine Wave Signal
Courtesy of BMW OF NORTH AMERICA, INC.

Voltage levels are dependent on sensor design.

Not all inductive sensors produce 12 volts.

Angle Pulse Generator

An Angle Pulse Generator Sensor acts on an existing AC voltage signal rather than produce a new one.

The sensor consists of two windings (primary and secondary) that are connected together at one end and a magnetic iron core (stationary) along with a trigger wheel (movable).

Fig. 5: Checking Angle Pulse Generator
Courtesy of BMW OF NORTH AMERICA, INC.

The primary winding (coil) is supplied with a 120kHz AC signal by the control module. The magnetic coupling (core) causes a voltage at the same frequency to be induced in the secondary winding. The induced frequency has a slight phase shift due the induction time delay.

The trigger wheel influences the magnetic field of the sensor and causes the phase shift to increase as the disc of the wheel moves closer to the sensor.

This changing of the phase shift (time delay) from a smaller time period to a larger time period and back again provides the control module with trigger wheel position.

The angle pulse generator provides position information regardless of movement. Trigger wheel position is established with the application of an output frequency from the control module and the return of the phase shifted signal.

Typical Application of Angle Pulse Generator

• Camshaft Sensor MS41.1.
• Pedal Request Sensor EML.

(a bank of three)

Fig. 6: Angle Pulse Generator Wave Signal
Courtesy of BMW OF NORTH AMERICA, INC.

DC Voltage Signals

Five Types of DC Voltage Signals Are Used:

• Analog Signals.
• Digital Signals.
• Designated Value Signals.
• Coded Ground Signals.
• Transistor Signals.

DC voltage signals are based on either 5 volts or 12 volts.

Fig. 7: Identifying DC Voltage Signals
Courtesy of BMW OF NORTH AMERICA, INC.

Analog Signals

Analog signals transmit information through an electrical circuit by regulating or changing the current or voltage.

The voltage of the signal has no fixed value. The value may be anywhere in the operating range of the signal.

Three sources of analog signals are:

• NTC Sensors.
• PTC Sensors.
• Potentiometers.

Fig. 8: Identifying Analog Signals
Courtesy of BMW OF NORTH AMERICA, INC.

NTC Sensors

NTC (Negative Temperature Coefficient) sensors change resistance based on temperature. As the temperature goes up the resistance goes down. This decrease in resistance causes the voltage drop across the sensor to decrease and the input signal voltage at the control module decreases.

Fig. 9: NTC Sensor Circuit Diagram
Courtesy of BMW OF NORTH AMERICA, INC.

Examples Of NTC Sensors

Intake Air Temperature Sensor

The intake air temp sensor provides a 0--5 volt analog signal to the DME indicating temperature of the incoming air.

The intake air temp sensor is located either in the intake manifold or integrated in the mass air flow meter.

Fig. 10: Checking Intake Air Temperature Sensor
Courtesy of BMW OF NORTH AMERICA, INC.

Engine Coolant Temperature Sensor

A dual sensor is used for engine temp. Operation is the same as other NTC sensors, 0-5 volt operating range, except that two independent sensors are housed in one assembly.

One is for the engine temperature input to the DME.

The other sensor is used to input engine temp to the instrument cluster.

Fig. 11: Checking Engine Coolant Temperature Sensor
Courtesy of BMW OF NORTH AMERICA, INC.

Typical Application of NTC Type sensor:

• Engine Coolant Temp Sensor.
• Intake Air Temp Sensor.
• Transmission Temp Sensor.

PTC Sensor

PTC (Positive Temperature Coefficient) sensors also change resistance based on temperature. In a PTC sensor as the temperature goes up the resistance also goes up. The increase in resistance causes the voltage drop across the sensor to increase and the input voltage signal at the control module increases.

Fig. 12: PTC Sensor Circuit Diagram
Courtesy of BMW OF NORTH AMERICA, INC.

Typical Application of A PTC Type Sensor:

• Exhaust Temp Sensor.
• Transmission Temp Sensor.

Example of PTC Sensor

A M5 Catalytic Convertor uses a PTC type sensor to monitor exhaust temperature.

A 0-12v signal is supplied to the DME indicating catalyst temperature.

Workshop Hints NTC/PTC Sensors:

When troubleshooting a faulty input display, the input signal must be verified as "good" BEFORE the control module is replaced.

When checking a NTC Sensor look for these voltages and problems:

0 volts = no supply voltage or shorted to ground.

2v = sensor is indicating a warm condition for system being measured.

4v = sensor is indicating a cold condition for system being measured.

5v = sensor or wiring harness is open.

Remember a PTC type sensor will indicate opposite results on intermediate readings (i.e. 4 volts = warm).

Potentiometers

A Potentiometer produces a gradually changing voltage signal to a control module. The signal is infinitely variable within the operating range of the sensor.

This varying voltage reflects a mechanical movement or position of the potentiometer wiper arm and its related components.

Fig. 13: Identifying Potentiometer
Courtesy of BMW OF NORTH AMERICA, INC.

Typical Application of Potentiometers:

• Air Flow Meter.
• Pedal Position Sensors.
• Seat and Mirror Memory Position.
• Throttle Position Sensors (Also Feedback Potentiometers).

Digital Signals

Digital Signals transfer information through an electrical circuit by switching the current on or off. Unlike analog signals which vary voltage, a digital signal has only two possible states, control voltage or 0 voltage.

Two types of Digital Signals:

• Switched (High/Low) Signals.
• Modulated Square Wave signals.

Switched B+ Signal

This DC voltage signal produces a YES/NO type input to the control module. The voltage level will indicate a specific operating condition.

Fig. 14: Digital Signals Transfer Information Chart
Courtesy of BMW OF NORTH AMERICA, INC.

Fig. 15: Identifying Brake Light Switch
Courtesy of BMW OF NORTH AMERICA, INC.

Hall effect Brake Light Switch

Fig. 16: Identifying DC Voltage Signal
Courtesy of BMW OF NORTH AMERICA, INC.

Typical Application of Switched B+:

• Ignition Switch.
• Seat Belt Switch.
• Light Switch.
• Hall Effect Switch (e.g. Brake Light Switch).
• Reed Switch.

Switched B- Signal

Fig. 17: Identifying (High/Low) Signal
Courtesy of BMW OF NORTH AMERICA, INC.

This Ground Signal produces a YES/NO type input to the control module. The voltage level will indicate a specific operating condition.

Fig. 18: Identifying Ground Signal
Courtesy of BMW OF NORTH AMERICA, INC.

Typical Application of Switched B-

• Door Position Switch.
• Kickdown Position Switch.
• A/C Pressure Switch.

Modulated Square Wave

A Modulated Square Wave is a series of High/Low signals repeated rapidly.

Like the switched signals (B+, B-) the square wave has only two voltage levels.

A high level and a low level.

Fig. 19: Identifying Modulated Square Wave
Courtesy of BMW OF NORTH AMERICA, INC.

A modulated square wave has 3 characteristics that can be modified to vary the signal:

• Frequency.
• Pulse Width.
• Duty Cycle.

Frequency

The frequency of a modulated square wave signal is the number of complete cycles or pulses that occur in one second. This number of cycles or frequency is expressed in Hertz (Hz). 1Hz = 1 complete cycle per second.

An output function may use a fixed or varied frequency.

Fig. 20: Identifying Modulated Square Wave Signal
Courtesy of BMW OF NORTH AMERICA, INC.

Pulse Width

The Pulse Width of a square wave is the length of time one pulse is ON. Vehicle systems may use fixed or varied ON times or pulse width. Pulse width is expressed in milliseconds (ms).

Fig. 21: Identifying Pulse Width Display
Courtesy of BMW OF NORTH AMERICA, INC.

Duty Cycle

The Duty Cycle of a square wave is the ratio of ON time to OFF time for one cycle.

Duty cycle is expressed in %.

Vehicle systems use both fixed duty cycle signals and variable duty cycle signals.

Fig. 22: Identifying Duty Cycle (1 Of 2)
Courtesy of BMW OF NORTH AMERICA, INC.

Fig. 23: Identifying Duty Cycle (2 Of 2)
Courtesy of BMW OF NORTH AMERICA, INC.

Time

1 second = 1000 milliseconds (ms).

1/2 second = 500 milliseconds.

1/4 second = 250 milliseconds.

1/10 second = 100 milliseconds.

1/100 second = 10 milliseconds.

1/1000 second = 1 milliseconds.

Hall-Effect Sensors

Hall Effect Sensors produce a modulated square wave.

Hall Effect Sensors are electronic switches that react to magnetic fields to rapidly control the flow of current or voltage ON and OFF.

The Hall Sensor consists of an epoxy filled non-magnetic housing containing a hall element and a magnet, and a trigger wheel.

Fig. 24: View Of Hall Effect Sensors
Courtesy of BMW OF NORTH AMERICA, INC.

The Hall element is a thin non-magnetic plate which is electrically conductive. (Voltage will flow through the plate.) Electron flow is equal on both sides of the plate.

Since everything between the magnet and the hall element is non-magnetic the magnet (magnetic field) has no effect on the current flow.

As a metal disk or solid area of a toothed wheel, flywheel or other trigger device approaches the sensor, a magnetic field is created between the magnet and the disk.

Fig. 25: Identifying Magnetic Field
Courtesy of BMW OF NORTH AMERICA, INC.

The magnetic field cause the electron flow to stop on one side of the plate. Electrons continue to flow on the other side of the plate.

The Hall Sensor Signal is a measurement of the voltage drop between the two sides of the plate or element.

When the magnetic field increases (disc or solid toothed area in front of sensor) the voltage drop across the two sides of the element increases. High voltage on one side, little on the other. The signal output from the sensor is High.

As the disc moves away from the sensor the magnetic fields weakens and is lost. The loss of the magnetic field ( blank toothed or open area of the wheel in front of the sensor) produces very little voltage drop across the two sides of the element. The output signal is Low.

This rapid switching of the voltage ON/OFF produces a HIGH/LOW signal that the control module uses to recognize speed and position.

Examples of Hall Effect Sensors

Motor Position Hall Sensors

Hall sensors are used on many electric motors to monitor speed and position. (i.e. electric window motors and sunroof motors.)

The Hall Effect principal is the same except the magnet is placed on the shaft of the motor.

The magnet is aligned to rotate in a precise position in front of the element. The polarization of the magnetic ring causes a polarity switch in the Hall element to occur as it rotates The square wave produced provides speed and position information to the control module.

Fig. 26: Identifying Motor Position Hall Sensors
Courtesy of BMW OF NORTH AMERICA, INC.

Wheel Speed Hall Effect Sensors

Hall Effect sensors are used to indicate wheel speed.

Conventional Hall Effect Sensors use three wires, power supply (usually 5v or 12v) a ground wire and a signal wire back to the control module.

The Hall Effect sensors used as wheel speed sensors are unique in that they are two wire Hall Effect Sensors.

The two wire sensors eliminate the separate ground wire and the signal wire functions as the ground also.

Fig. 27: Identifying Wheel Speed Hall Effect Sensors
Courtesy of BMW OF NORTH AMERICA, INC.

The unique two wire arrangement provides the control module with a HIGH/LOW signal having a low voltage of .75 volts and a high voltage of 2.5 volts.

Typical Application of Hall Effect sensors

• Crankshaft Sensors.
• Motor Position and Speed Sensors (e.g. Window Motor, Sunroof Motor).
• Camshaft Sensors.
• Wheel Speed Sensors.

Magnetoresistive Sensors

The active sensing of the Magnetoresistive Sensor is particularly suitable for advanced stability control applications in which sensing at zero or near zero speed is required.

A permanent magnet in the sensor produces a magnetic field with the magnetic field stream at a right angle to the sensing element.

Fig. 28: Exploded View Of Magnetoresistive Sensors
Courtesy of BMW OF NORTH AMERICA, INC.

The sensor element is a ferromagnetic alloy that changes its resistance based on the influence of magnetic fields.

As the high portion of the pulse wheel approaches the sensing element a deflection of the magnetic field stream is created. This creates a resistance change in the thin film ferromagnetic layer of the sensor element.

Fig. 29: View Of Sensor Element
Courtesy of BMW OF NORTH AMERICA, INC.

The sensor element is affected by the direction of the magnetic field, not the field strength. The field strength is not important as long as it is above a certain level. This allows the sensor to tolerate variations in the field strength caused by age, temperature, or mechanical tolerances.

The resistance change in the sensor element affects the voltage that is supplied by the evaluation circuit. The small amount of voltage provided to the sensor element is monitored and the voltage changes (1 to 100mv) are converted into current pulses by the evaluation module.

Fig. 30: Identifying High And Low Current Pulses
Courtesy of BMW OF NORTH AMERICA, INC.

• Signal Low-7mA.
• Signal High-14mA.

The sensor is supplied 12V by the control unit. Output voltage from the sensor is approximately 10V. The control unit counts the high and low current pulses to determine the wheel speed.

Typical Application of Magnetoresistive Sensor:

• Found Currently on E46 with Teves DSCIII MK-60.

Designated Value Signals

Designated values are produced through fixed resistance positions of a multi-position switch. As the switch is operated the voltage drop across the resistor(s) of each switch position causes the voltage level of the input signal to change to a predetermined voltage value.

These predetermined (designated) voltages signal the control module to perform specific functions.

Fig. 31: Identifying Designated Value Signals
Courtesy of BMW OF NORTH AMERICA, INC.

Voltage Values seen as input by control module.

Fig. 32: Voltage Values Display
Courtesy of BMW OF NORTH AMERICA, INC.

Typical Application of Designated Values:

• Cruise Control Switch On E 32.
• Seat and Mirror Memory Position Buttons.

Coded Ground Signals

Coded ground signals produce a set of High/Low requests, the combination (pattern) of which is interpreted by the control module to perform a specific function. Coded ground signals are generated through a switch or series of switches signaling the control module requests for operation.

Fig. 33: Identifying E 36 Wiper Circuit
Courtesy of BMW OF NORTH AMERICA, INC.

Fig. 34: Identifying E 39 Wiper Circuit
Courtesy of BMW OF NORTH AMERICA, INC.

Transistor Function

The transistor takes on a number of applications that must be understood to effectively analyze a circuit.

The transistor in operation functions as two parts much like a relay. Both the relay and the transistor control high currents with a low current signal.

Fig. 35: Identifying Transistor Final Stage Function (1 Of 2)
Courtesy of BMW OF NORTH AMERICA, INC.

The base/emitter path functions as the control circuit activated by the control module to oversee or control the work.

The collector/emitter path functions as the work side of the circuit, supplying power or switching on the work.

In operation the transistor can be switched ON momentarily, or supply a constant power or ground.

The transistor can also be modulated or pulsed to supply a modulated square wave signal.

Fig. 36: Identifying Transistor Final Stage Function (2 Of 2)
Courtesy of BMW OF NORTH AMERICA, INC.

Modulated, Momentary, Constant B- as Input/Output

The input signal of control module 1 is an output signal of control module 2.

Control module 2 through activation of its internal transistor provides a ground input for control module 1.

Fig. 37: Identifying Modulated, Momentary, Constant B- As Input/Output Function
Courtesy of BMW OF NORTH AMERICA, INC.

The input signal at control module 1 is either a momentary/constant signal (i.e torque convertor signal from TCM to DME) or a modulated signal (i.e. vehicle speed signal ASC to DME).

Fig. 38: Identifying Wheel Speed Signal And Output Pulse
Courtesy of BMW OF NORTH AMERICA, INC.

Typical Application of Modulated, Momentary, Constant B- as Input/Output Signal:

• A/C KO Signal.
• Speed Signal From ABS/ASC.
• TI/TD Output Signal From DME.

Momentary/Constant B⁺ as an Input/Output Signal

Fig. 39: Identifying Momentary/Constant B As An Input/Output Signal Function
Courtesy of BMW OF NORTH AMERICA, INC.

Typical Application of Momentary/Constant B⁺ as an Input/Output Signal:

• OBC Code Signal to DME.
• A/C Signal to DME.

Constant B-/B+ To Energize a Component

Constant B-

Output function to energize a component.

Relay is energized by control module.

Internal activation of the transistor provides a ground for the relay coil.

Fig. 40: Identifying Output Function To Energize Component (Constant B-)
Courtesy of BMW OF NORTH AMERICA, INC.

Constant B+

Fig. 41: Identifying Output Function To Energize Component (Constant B+)
Courtesy of BMW OF NORTH AMERICA, INC.

Control module output function to energize a component.

Transistor controls output function of the control module.

Control module supplies power to the relay. The relay is activated by the control module through internal activation of the transistor which provides a ground for the relay coil.

Modulated B-/B+ To Operate A Component

Modulated B-

Output function to operate a component.

The idle valve motor is operated by the control module through internal activation of the transistor which provides a ground for the open winding of the valve.

The idle control valve is operated by regulation of the duty cycle at a specific frequency.

Fig. 42: Identifying Output Function To Operate Component (Modulated B-)
Courtesy of BMW OF NORTH AMERICA, INC.

Typical Application of modulated B-

• Idle Control Motor.
• Purge Valve.
• Injector.
• Ignition Coil.

Modulated B+

Fig. 43: Identifying Output Function To Operate Component (Modulated B+)
Courtesy of BMW OF NORTH AMERICA, INC.

Output function to operate a component.

The motor is controlled by a transistorized function of the control module, which provides a modulated voltage at a specific frequency to the motor. The throttle position is changed by altering the Duty Cycle of the pulses.