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Technician Handbook 673 Electronic & Computer Controlled Systems Section Topics Electronic Control Units Technical Training • Electronic Control Units • Logic Function • Simple ECU Inputs • Simple ECU Outputs • Self-Diagnosis • Memory • Customization • Initialization Technician Handbook 673 Electronic & Computer Controlled Systems Electronic Control Units Electronic Control Units (ECUs) are small computers programmed to perform specific automotive functions What are some typical automotive ECUs? ECUs use electronic components in integrated circuits to perform their functions Electronic Control Units In the 1970’s, the decreasing cost and increasing power of computerized microprocessors launched the personal computer industry Because of their speed and flexibility in carrying out complex functions, microprocessors were adapted for hundreds of uses beyond personal computers The first microprocessors began appearing in automotive engine control systems in the early 1980s In automotive applications, they became known as electronic control units (ECUs) Today, some vehicles may have dozens of ECUs controlling a wide variety of vehicle systems, including: • engine controls • transmission • braking • steering • air conditioning • door locks • suspension • cruise control • tire pressure monitoring • and many other systems Technical Training Technician Handbook 673 Electronic & Computer Controlled Systems ECU Logic Function ECUs have electronic logic circuits that “make decisions” by evaluating conditions according to predetermined rules Light Control SW Headlights Light Control Sensor Body ECU How ECUs Work Conditions IF Light control switch is in the AUTO position and Light control sensor detects LOW ambient light and Ignition switch is ON Decision Taillights THEN Turn headlights ON Turn taillights ON An ECU is a small computer programmed to perform a specialized function in the vehicle As with any computer, it operates on the principle of input, processing, and output Input – Information about conditions is supplied to the ECU as input signals Input can be provided by: • sensors • switches • other ECUs Processing – The ECU analyzes the input signals Based on its programming, it determines what output signals to send, if any Output – Vehicle systems are controlled by the ECU output signals These signals may cause a motor to operate, a light to come on, or some other operation of a vehicle component Logic Function For an example of the ECU’s logic function, consider the lighting control system which is within the Body ECU A simple lighting control system uses three inputs – the light control switch, the light control sensor, and the ignition switch When the condition of these three inputs matches the conditions preprogrammed in the ECU, the ECU turns on the headlights and taillights Technical Training Technician Handbook 673 Electronic & Computer Controlled Systems Simple ECU Inputs Voltage ON/OFF Voltage Pulse Pattern Combination Switch Active Speed Sensor MRE A MRE B Sensor IC Variable Voltage Variable Resistance What are some other types or examples of ECU inputs? Oxygen Sensor Temp Sensor Exhaust Gas Simple ECU Inputs Signals from switches and sensors can supply information to the ECU in several ways Voltage ON/OFF – A simple switch opens or closes a circuit It is the presence or absence of voltage in the circuit that signals the ECU Variable Voltage – Some sensors produce a voltage that changes depending on the conditions the sensor is measuring The amount of voltage produced at any given moment provides information about the condition at that time Variable Resistance – In other types of sensors, electrical resistance increases or decreases as external conditions change Sensing the changing voltage as a result of changing resistance in the circuit signals the ECU what the conditions are Variable Pulse Pattern – Another method for signaling the ECU about changing conditions is to turn a circuit on and off rapidly at a particular frequency This works especially well for signaling rotational speed It is the frequency of the ON/OFF pulses that supplies information to the ECU Technical Training Technician Handbook 673 Electronic & Computer Controlled Systems Voltage ON/OFF (Switch) Input The ECU detects the state of a ground-side switch by reading the circuit voltage When switch ON is detected, the ECU performs a function, such as turning on a lamp B+ B+ OFF: V = 12.6V (open circuit voltage) 0V ECU 12.6V Ground-side switched 12.6v ON: V = 0.1V (available voltage) * 5V ECU 12.6V 0.1v * Voltage can also be measured at the ECU terminal * Conceptual illustration only Voltage ON/OFF (Switch) Input The diagrams above illustrate a ground-side switch connected to an ECU The ECU supplies battery voltage to the switch circuit and provides the circuit’s load (a resistor) The ECU’s electronic circuits detect when the voltage after the load is high (near battery voltage) or low (near ground voltage) While the switch is open, no current is flowing and the available voltage after the load is near battery voltage When the switch is closed, current flows and most of the battery voltage is dropped across the load The available voltage after the load is now near ground voltage In this example, the switch controls a lamp, but is not actually part of the lamp circuit When the ECU senses a voltage drop in the switch circuit, it supplies five volts to the transistor This in turn closes the lamp circuit, lighting the lamp SERVICE TIP NOTE Technical Training You can detect the same high or low voltage the ECU is detecting by measuring voltage at the appropriate ECU terminal If the switch is closed and the voltage remains high, you’ll know there is an open in the circuit between the ECU and the switch The actual wiring inside the ECU is extremely complex The ECU circuit details shown in the diagrams above and the diagrams on the following pages are to illustrate concepts, not actual internal connections Technician Handbook 673 Electronic & Computer Controlled Systems Variable Voltage Input The oxygen sensor is a voltage generator The engine control module interprets the voltage to make corrections to the air-fuel ratio Voltage V Atmosphere ECM V > 0.45v : air-fuel ratio too rich V = 0.45v : air-fuel ratio correct V < 0.45v : air-fuel ratio too lean Exhaust Gas Variable Voltage Input An oxygen sensor is a voltage generator, producing between 0.1v and 0.9v depending on the oxygen content of the exhaust gas compared to the atmosphere The engine control module’s electronic circuits measure the amount of voltage generated by the oxygen sensor, and use that information to control the air-fuel ratio 10 Technical Training Technician Handbook 673 Electronic & Computer Controlled Systems Variable Resistance Input A temperature sensor is a type of variable resistor Its resistance changes with temperature 12.6V or 5V V An ECU can detect the change in the sensor’s resistance by measuring voltage ECU Variable Resistance Input A temperature sensor is a type of variable resistor whose resistance changes with temperature This type of sensor is often called a thermistor Two types of thermistor are: Positive temperature coefficient (PTC) thermistor – resistance increases as temperature increases Negative temperature coefficient (NTC) thermistor – resistance decreases as temperature increases Thermistors are commonly used for engine coolant temperature sensors and ambient temperature sensors Modern Toyota vehicles use NTC thermistors exclusively Technical Training 11 Technician Handbook 673 Electronic & Computer Controlled Systems Pulse Pattern Input An active wheel speed sensor generates a series of voltage pulses as the wheel rotates MRE A MRE B Sensor IC As rotation speed increases, pulses are generated at a higher frequency The ECU measures the pulse frequency to calculate vehicle speed Voltage Voltage Lower Rotation Speed Time Pulse Pattern Input Higher Rotation Speed Time Another type of ECU input is a pulse pattern When voltage rises momentarily, then falls, the transient voltage reading is called a pulse When a component creates multiple pulses, the result is a pulse pattern (or pulse train) An active wheel speed sensor is a component that generates a pulse pattern A magnetic ring mounted on the wheel hub has alternating north-south fields that are detected by the sensor pickup As the wheel rotates, the alternating magnetic fields are converted into a series of voltage pulses The frequency of the pulses increases with the wheel rotation speed When the pulse pattern is provided as ECU input, the ECU’s circuits are able to measure the pulse frequency and calculate wheel RPM and vehicle speed 12 Technical Training Technician Handbook 673 Electronic & Computer Controlled Systems Simple ECU Outputs When the operating conditions are met, the ECU makes a connection to power or ground to energize a circuit ECU NPN B+ How a Transistor Works (NPN) Transistor 5V Ground-side controlled circuit ECU B+ Collector When voltage is applied to the base… current can flow from the collector to the emitter Base PNP Emitter Power-side controlled circuit A See Appendix for More Info Simple ECU Outputs The simplest way for an ECU to control a vehicle function is to turn a circuit on or off A circuit can be ground-side switched or power-side switched Transistors as Switches Electronic circuits use transistors for switching circuits on and off A transistor is a solid-state electronic component having a base, collector and emitter In the more commonly used NPN transistor, when sufficient voltage is applied to the base, current flows from the collector to the emitter One of the advantages of the transistor is that a low voltage at the base is able to control a large current flowing through the collector and emitter In that respect, a transistor is similar to a relay Some transistors also regulate current flow based on the amount of voltage applied to the base Within the transistor’s limits, a higher base voltage results in a greater flow of current through the collector/emitter This feature is used in amplifier circuits where the low voltage signal from a microphone regulates current flow in higher power speaker circuits Technical Training 13 Technician Handbook 673 Electronic & Computer Controlled Systems Pulse Width Modulation The ECU can open and close a circuit rapidly to control component operation The process of varying the amount of time a circuit is ON is called pulse width modulation Example Voltage Pulses The ECM regulates the injector ON time by regulating the width of the voltage pulse to the injectors Pulse Width Notice the pulse width increases at higher load as the ECM increases the injector ON time Pulse Width Modulation An ECU’s electronic circuits have the ability to open and close a circuit very rapidly The ECU can switch a circuit on for a fraction of a second at very precise intervals When a circuit is switched ON and then OFF, the momentary change in voltage creates a voltage pulse (The pulse can be either a momentary increase or decrease in voltage depending on whether the circuit is ground-side switched or power-side switched and where the voltage is measured.) When the voltage is viewed on an oscilloscope, the voltage pulse’s width represents the amount of time the circuit is switched ON and can be as brief as millisecond or less In some circuits, the ECU uses the amount of ON time to regulate component operation When the ECU varies the width of the voltage pulse (the ON time) to control a component, the process is called pulse-width modulation NOTE 14 In the above example, the frequency of the pulses changes as well as the pulse width In some circuits, the frequency of the pulses is constant Technical Training Technician Handbook 673 Electronic & Computer Controlled Systems Measuring Duty Cycle When the ECU modulates a circuit at a constant frequency, you can measure the circuit’s duty cycle Duty cycle is the percentage of ON time compared to total cycle time Varying the duty cycle can vary the brightness of a lamp or the speed of a motor ECU B+ If the percentage of ON time decreases, the lamp becomes dimmer 5V 12 V 12 V 0V 0V cycle (100%) 75% ON (grounded) cycle (100%) 25% ON (grounded) In a ground-side controlled circuit, measure after the load Duty Cycle The terms pulse-width modulation and duty cycle are often confused or used incorrectly Pulse-width modulation is a function an ECU can perform to turn a circuit on and off rapidly to regulate the amount of ON time As the pulse width changes, the frequency of the pulses might or might not change depending on the circuit design and intended operation When a circuit is switched on and off rapidly at a constant frequency, duty cycle measures the percentage of ON time compared to total cycle time If the circuit is ON 75% of the time, it is operating at a 75% duty cycle When a circuit is duty-cycle controlled, the pulse frequency does not change – only the percentage of ON time An ECU varies the duty cycle to control the speed of a motor or the brightness of a lamp by switching the circuit ON and OFF hundreds of times per second Human senses can’t perceive a lamp or motor being cycled on and off that quickly Nonetheless, the amount of power to the component increases or decreases depending on how much of the time the circuit is ON versus OFF As OFF time increases, the net power supplied to a component decreases resulting in the lamp becoming dimmer or the motor running slower As ON time increases, power increases and the lamp becomes brighter or the motor runs faster NOTE Technical Training When the circuit is ground-side controlled, voltage before the load is always battery voltage, and voltage after the switch is zero, or near zero To observe voltage modulation, place the positive probe between the load and the switch (which may be an ECU) 15 Technician Handbook 673 Electronic & Computer Controlled Systems Measuring Duty Cycle Signals in a power-side controlled circuit are the opposite of signals in a ground-side controlled circuit ECU B+ If the percentage of ON time decreases, the lamp becomes dimmer cycle (100%) cycle (100%) 75% ON (powered) 25% ON (powered) In a power-side controlled circuit, measure before the load Power-Side Control Most circuits in Toyota vehicles are ground-side controlled When a pulsewidth modulated circuit is power-side controlled, the voltage modulation is observable after the ECU and before the load In this arrangement, the circuit is ON when the voltage rises Note that if voltage is measured after the load, a very minute change in voltage occurs as the circuit is modulated At this point in the circuit, voltage is zero when the circuit is open When the circuit is closed, ground voltage is present The difference is usually less than 0.1V and may not be observable depending on your scope settings 16 Technical Training Technician Handbook 673 Electronic & Computer Controlled Systems Self-Diagnosis The ECU’s internal wiring can be arranged so it can detect when an input circuit is open or shorted to ground ECM Throttle Position Sensor Under normal conditions, the ECM senses more than 0V and less than 5V at VTA and VTA2 VTA VC 5V VTA2 E2 DTC P0120 With either a short or an open in the input circuit, voltage at VTA and VTA2 becomes 0V and the ECU sets a DTC Throttle/Pedal Position Sensor/Switch “A” Circuit Malfunction 2002 Tundra V8 Self-Diagnosis A significant reason ECUs have become so common in automobile systems is their ability to perform self-diagnosis ECUs can identify faults in circuits, components, and even within the ECU itself When a fault is detected, the ECU can: • Illuminate a warning light • Set a diagnostic trouble code • Begin operating in a fail-safe mode by: ◦ Disabling a system that is working incorrectly ◦ Using sensor data from alternate sources ◦ Applying alternate rules for operating the vehicle or subsystem to maintain maximum safety Differences in SelfDiagnosis An ECU’s self-diagnosis capabilities can range from very simple to highly sophisticated Each ECU has its own features and limitations, and very few work in exactly the same way The example above is a throttle position sensor circuit The electronics inside the engine control module (ECM) are designed so that an open or a short to ground on VTA or VTA2 can be detected and a DTC set The circuit arrangement inside the ECM is not able to distinguish a short from an open, however In either case, the voltage the ECM is monitoring goes to 0V Technical Training 17 Technician Handbook 673 Electronic & Computer Controlled Systems Self-Diagnosis ECUs can be wired so they can detect the difference between an open or short, and set a different DTC for each ECM Throttle Position Sensor In this arrangement, what is the normal voltage at VTA1? What is the voltage with a short in the circuit? VTA1 VC 5V VTA2 E2 DTC P0122 Throttle/Pedal Position Sensor/Switch “A” Circuit Low Input DTC P0123 Throttle/Pedal Position Sensor/Switch “B” Circuit High Input Differences in SelfDiagnosis (Cont’d) What is the normal voltage at VTA2? What is the voltage with an open in the circuit? 2003 Tundra V8 In this throttle position sensor circuit, the electronics inside the ECM are arranged slightly differently In this arrangement, a short to ground on a VTA line causes the monitored voltage to go to 0V An open in a VTA line, however, causes the monitored voltage to go to 5V Thus, this ECM can distinguish between an open or short on an input circuit and can set a DTC for one or the other The additional data supplied by the ECM makes it easier and faster to diagnose and correct the problem 18 Technical Training Technician Handbook 673 Electronic & Computer Controlled Systems ECU Memory ECUs have different types of memory • DTCs • Driver preferences • Vehicle operating characteristics ECU program logic ECU program logic, data (reflash) B+ ECU Memory RAM (volatile) ROM (permanent) EEPROM (reprogrammable) ECU Memory Like other computers, ECUs have internal memory Besides storing DTCs, they can also store switch settings and component positions Over time, ECUs can acquire and store information about the vehicle’s operating characteristics and driver/occupant preferences The data stored in memory can have a direct affect on how well the vehicle operates and the driver’s perceptions of comfort and convenience Types of ECU Memory Volatile memory chips are the type that require constant power to maintain what is stored in them When the power is removed, their memory contents are erased These types of memory chips are used for ordinary microprocessor memory (RAM for example.) Non-volatile memory chips retain their contents even when the power is removed These types of memory chips permanently store the microprocessor’s operating instructions, or logic (ROM for example.) Programmable Read Only Memory (PROM) – A memory chip that can be programmed once, but cannot be reprogrammed Erasable Programmable Read Only Memory (EPROM) – A programmable chip that can be removed from its circuit and reprogrammed Electrically Erasable Programmable Read Only Memory (EEPROM) – A programmable chip that can be electrically erased and reprogrammed without removing it from the circuit Technical Training 19 Technician Handbook 673 Electronic & Computer Controlled Systems ECU Customization Because ECUs have memory, they can be programmed with owner/driver preferences A Would you like the interior light turned ON when the doors are unlocked? B C Would you like the interior light turned ON when the ignition is turned OFF? Main Body ECU ECU Memory A Yes Customization B Yes C 30 seconds How long would you like the interior lights to be left ON? No matter how carefully automobile manufacturers analyze the features that new car buyers want, there will always be those who want a feature to work differently ECUs have made it much easier for owners to customize many of the vehicle’s convenience features to suit their own preferences The settings for customizable features are stored in ECU memory Needless to say, if the memory is lost then any preferences the owner has chosen are also lost Memory can be lost when the ECU loses its connection to the battery, and also when the ECU is replaced SERVICE TIP NOTE 20 Before disconnecting the battery, make note of the owner’s customized settings and restore those settings when service is complete When one driver changes a customized setting without informing other drivers, another driver may view the change in operation as a malfunction Be sure to consider the potential role of customized settings on a customer’s concern before beginning a problem diagnosis Technical Training Technician Handbook 673 Electronic & Computer Controlled Systems ECU Initialization Initialization procedures can be very different depending on the ECU Examples Headlamp Leveling ECU Initialization Driver’s Door Power Window Initialization (Body ECU) • Unload the vehicle • Turn ignition ON • Jumper terminals and of DLC3 • Hold the switch to open the window • Flash the headlights times • Hold the switch to close the window • Keep holding the switch until the switch stops blinking Completely Closed Initialization ECUs may need to be initialized when: • A new ECU is installed • Key components related to the ECU’s operation have been replaced • Loss of power erases critical memory settings Initializing an ECU simply means preparing it for operation If an ECU is not initialized when required: • The system may be inoperable or operate incorrectly • Some system features may be disabled Why Initialize? When an ECU is installed, it becomes part of a system of interconnected components Many ECUs are designed to work in systems with optional components in sometimes varying configurations Before the ECU can begin operation, it must learn the configuration of the system it’s connected to, and sometimes obtain data from other components This takes place during initialization When initialization is completed, the ECU has acquired the information it needs to begin performing its function In quite a few vehicle systems, ECUs control motors, such as power window motors and power back door motors These systems require initialization in particular so the ECU can synchronize itself with the motor to control the opening and closing function properly In systems with jam protection, this feature may be inoperable until the ECU has been initialized NOTE Technical Training Before determining an ECU is faulty, first verify that it doesn't just need to be initialized 21 673 Electronic & Computer Controlled Systems Technician Handbook This Page Intentionally Left Blank 22 Technical Training ... circuit and can set a DTC for one or the other The additional data supplied by the ECM makes it easier and faster to diagnose and correct the problem 18 Technical Training Technician Handbook... the ECU’s circuits are able to measure the pulse frequency and calculate wheel RPM and vehicle speed 12 Technical Training Technician Handbook 673 Electronic & Computer Controlled Systems Simple... ECM senses more than 0V and less than 5V at VTA and VTA2 VTA VC 5V VTA2 E2 DTC P0120 With either a short or an open in the input circuit, voltage at VTA and VTA2 becomes 0V and the ECU sets a DTC