Section Input Sensors Slide 30 T852f007 Input Sensors There are three types of input sensors: • ON/OFF switches (ECM can determine which one of two operating conditions) — for example, the stop lamp switch allows the ECM to determine if the brake pedal is depressed or not • Variable sensors (ECM can determine a range of operating conditions) — for example, the engine coolant temperature sensor allows the ECM to determine temperature in a wide range, from below freezing to above boiling • Frequency sensors — for example, the knock sensor detects frequencies that allow the ECM to make adjustments and prevent engine knock Toyota Engine Control Systems I Course 852 27 Power Side vs Ground Side Input Sensors Slide 31 T852f019/T852f024 Power Side vs Ground Side Input sensor switches are located in one of two places: • Power side — between the power source and the ECM In the example shown, when the switch is open, there is no voltage at the ECM The stop lamp switch is a typical example of a power side switch • Ground side — between the ECM and ground In the example shown, when the switch is open, the ECM reads supply voltage When the switch is closed, the ECM will read near volts The cruise control switch is a typical example of a ground side switch 28 TOYOTA Technical Training Position and Mode Switches Input Sensors Slide 32 PPN Switch Position and Mode Switches Simple multi-position switches allow the ECM to determine the position or mode of various vehicle systems or components Examples include: • Stop lamp switch • Ignition switch • Park/Neutral switch • Transfer Low position detection switch • Transfer Neutral position detection switch • Transfer 4WD detection switch Operation Diagnosis Position and mode switches can be placed on the power or ground side of the ECM They may respond directly to driver input (such as stop lamp switch) or to changes in vehicle operating condition (such as power steering pressure switch) Be sure the fault is in the switch itself (not a short or open in the circuit wiring or an ECM fault) Most switches can be tested with a DVOM If the switch fault has set a DTC, follow the complete DTC troubleshooting procedure outlined in the Repair Manual Toyota Engine Control Systems I Course 852 29 Temperature Sensors Input Sensors Slide 33 T852f034/T852f037/T852f065/T852f035/T852f038 Temperature The ECM adjusts a variety of systems based on temperatures It is critical Sensors for proper operation of these systems that the engine reach operating temperature and the temperature is accurately signaled to the ECM For example, for the proper amount of fuel to be injected, the ECM must know the correct engine temperature The two main temperature sensors used for engine control are ECT and IAT • The Engine Coolant Temperature (ECT) sensor responds to changes in engine coolant temperature and is usually located in a coolant passage just before the thermostat The ECT sensor signal is critical to many ECM functions including fuel injection, ignition timing, variable valve timing, and transmission shifting • The Intake Air Temperature (IAT) sensor detects the temperature of the air stream entering the engine It is usually built into the Mass Air Flow (MAF) sensor located in the air intake tube The IAT sensor signal is used by the ECM to modify fuel injection and engine diagnostic routines 30 TOYOTA Technical Training Temperature Sensor Operation Input Sensors Slide 34 Operation Though the ECT and IAT sensors measure different temperatures, they operate the same way The voltage signal from the sensor tells the ECM what the temperature is at the sensor As the sensor heats up, the voltage signal decreases This decrease in voltage signal is caused by a decrease in sensor resistance The temperature sensor is connected in series to a fixed value resistor inside the ECM The ECM supplies volts to the circuit and measures the change in voltage between the fixed value resistor and the temperature sensor: • When the sensor is cold, its resistance is high, and the voltage signal is high • As the sensor warms up, its resistance drops, and the voltage signal decreases Toyota Engine Control Systems I Course 852 31 Temperature Sensor Diagnosis and Testing Input Sensors Slide 35 T852f041/T852f047 Diagnosis The purpose of a temperature sensor diagnostic procedure is to isolate and identify sensor faults as opposed to circuit and ECM faults Temperature sensor circuits are tested for: • Open circuit: An open circuit (high resistance) will read the coldest temperature possible (-40ºF) • Short circuit: A shorted circuit (low resistance) will read the highest temperature possible (284ºF) • Available voltage • Sensor resistance Note that at the upper end of the temperature/resistance scale, sensor resistance changes very little Extra resistance in the circuit at higher temperatures can cause the ECM to think the reading is approximately 20ºF–30ºF colder than actual temperature The Techstream Data List can help reveal such inaccurate readings Testing 32 To test a temperature sensor for accuracy, compare the resistance of the sensor to the actual temperature For the ECT, this process usually involves monitoring the resistance of the sensor in water as the temperature is gradually raised The Repair Manual contains the modelspecific procedure and specifications To ensure accuracy, you must have an accurate thermometer and good electrical connections to the DVOM TOYOTA Technical Training Position Sensors Input Sensors Slide 37 T852f048/230LX12 Position Sensors The two most common position sensors are: • Throttle Position Sensor (TPS): indicates the position of the throttle valve • Accelerator Pedal Position Sensor (APPS): indicates the position of the accelerator pedal Position sensors may be a mechanical (contact) type or electronic (noncontact) type For reliability, many late-model sensors create multiple outputs, allowing the ECM to double-check their signals Toyota Engine Control Systems I Course 852 33 Operation — Single Output Contact Type TPS Input Sensors Slide 38 T852f049/T852f050/T852f054/T852f055 Operation — Single Output Contact Type TPS The TPS is mounted on the throttle body and contains a resistor and a wiper arm There are three sensor terminals: • Five volts are supplied to the TPS from the VC terminal of the ECM • The TPS voltage signal is supplied to the VTA terminal • A ground wire from the TPS to the E2 terminal of the ECM completes the circuit The wiper arm is always in contact with the resistor and moves with the throttle blade The available voltage at the point of contact between the arm and resistor is sent through the VTA wire to the ECM and interpreted as throttle position • At idle, the wiper arm is far from the VC terminal and resistance is high Therefore, the available voltage at the VTA terminal is low (approximately 0.6 to 0.9 volts) • At wide open throttle, the wiper arm is close to the VC terminal and resistance is low Therefore, the available voltage at the VTA terminal is high (approximately 3.5 to 4.7 volts) 34 TOYOTA Technical Training Input Sensors Operation — Dual Output Contact Type TPS Slide 39 Operation — Dual Output Contact Type TPS Vehicles equipped with Electronic Throttle Control System-intelligent (ETCS-i) have a dual output TPS Dual output contact type TPS works the same as a single output contact type, but it has two contact arms and two resistors in one housing • One signal to the ECM is usually called VTA • The second signal to the ECM is usually called VTA2 VTA and VTA2 both increase in voltage output as the throttle valve is opened, but VTA2 starts at a higher voltage output and the voltage change rate is different from VTA Note in the graph that VTA2 reaches its upper limit earlier than VTA The ECM uses both signals to detect the change in throttle valve position By having two signals in one sensor, the ECM can compare the voltages and detect sensor problems The two signals not provide redundancy Toyota Engine Control Systems I Course 852 35 Operation — Dual Output Non-Contact Type TPS Input Sensors Slide 40 230LX12/238EG79 Operation — Dual Output Non-Contact Type TPS The output signals from a non-contact TPS are similar to those from a contact type TPS However, as its name implies, the non-contact type TPS does not use a wiper arm and resistor to determine the position of the throttle valve The non-contact TPS is a Hall effect sensor Two Hall ICs are mounted on the throttle body and surrounded by a magnetic yoke As the throttle valve moves, the yoke moves around the Hall ICs, causing changes in the magnetic field surrounding the Hall ICs The Hall ICs convert these changes into electrical signals and output them to the ECM (usually as VTA1 and VTA2) Like the dual output contact type TPS, the two unique signals allow the ECM to compare output and detect faults, and not provide redundancy This electronic sensor is more durable than contact type sensors because it does not depend on physical contact between components 36 TOYOTA Technical Training Pickup Coil Sensor Operation Input Sensors Slide 51 T852f098/T852f099 Operation — Pickup Coil Type Pickup coil type sensors consist of a permanent magnet, yoke, and coil The sensor is mounted close to a toothed gear called a rotor • As each tooth moves by the sensor, an AC voltage pulse is induced in the coil Each tooth produces a pulse (Not all rotors use teeth Sometimes the rotor is notched, which produces the same effect.) • As the gear rotates faster, more pulses are produced The ECM determines the speed of component rotation based on the number of pulses in one second (signal frequency) The distance between the rotor and pickup coil is critical The farther apart they are, the weaker the signal These sensors generate AC voltage and not need an external power supply Another common characteristic of pickup coil type sensors is the two wires carrying AC voltage The wires are twisted and sometimes shielded, to prevent electrical interference from disrupting the signal (the EWD will indicate if the wires are shielded) 46 TOYOTA Technical Training Input Sensors MRE Sensor Operation Slide 52 T852f109_v2 Operation — MRE Type Engine control magnetic resistance element (MRE) type sensors require an external power supply to operate The sensors include: • A magnetic resistance element that changes electrical resistance in response to changing magnetic field strength • Circuitry that converts an analog AC wave to a digital signal As the timing rotor turns, each lobe causes a change in the magnetic field, which affects the resistance of the MRE Constant voltage applied to the MRE is varied by the changing resistance, generating a waveform Circuitry inside the sensor converts the analog wave to a digital voltage signal that the ECM reads as component speed and/or position Toyota Engine Control Systems I Course 852 47 MRE vs Pickup Coil Input Sensors Slide 53 232CH41 MRE vs Pickup Coil Because engine control MRE sensors use an external power source, they can produce reliable signals at very low rotational speeds Internal circuitry converts the analog waveform to a consistent digital signal Pickup coil type sensors rely on the rotational speed of the component to generate signal strength, so their signal can be weak or nonexistent at low speeds The ECM must include circuitry to interpret the pickup coil’s analog waveform output 48 TOYOTA Technical Training Input Sensors Pickup Coil Position Sensors Slide 54 T852f100/T852f101/T852f102 Pickup Coil Camshaft Position Sensor (G Sensor) A toothed rotor on the camshaft allows the ECM to determine when cylinder No is on the compression stroke This information is used to control fuel injection timing, ignition timing, and variable valve timing In this pickup coil style sensor, the AC signal is directly proportional to camshaft speed That is, as the camshaft revolves faster, the signal frequency increases Pickup Coil Crankshaft Position Sensor (NE Sensor) Pickup Coil NE and G Signals A toothed rotor on the crankshaft allows the ECM to determine crankshaft position This “NE signal” helps the ECM determine engine speed, crankshaft position, and engine misfire The NE signal combined with the G signal indicates the cylinder that is on its compression stroke The ECM compares the NE and G signals to determine which cylinder is on its compression stroke • The periodic gap in the NE signal is caused by the irregular tooth pattern of the timing rotor • The ECM uses these gaps as reference to crankshaft position • When combined with the G signal, the ECM can determine piston position and stroke Toyota Engine Control Systems I Course 852 49 MRE Position Sensors Input Sensors Slide 55 285EG82/285EG83/285EG84/036EG111TE MRE VVT Position Sensors On engines with variable valve timing, camshaft position sensors are often called VVT sensors MRE sensor technology may be used to generate accurate, reliable camshaft position signals at all engine speeds MRE VVT Sensor Waveforms The VVT sensor’s irregular rotor design produces pulses (3 high and low) for every two crankshaft revolutions The ECM compares this signal to crankshaft position sensor output to accurately determine camshaft position MRE Crankshaft Position Sensors MRE Crankshaft Position Sensor Waveforms 50 Some late model vehicles use an MRE type crankshaft position sensor to determine crankshaft position and engine speed This type of sensor generates an extremely accurate signal at all engine speeds The timing rotor for the crankshaft position sensor has 34 teeth with teeth missing Based on these teeth, the crankshaft position sensor transmits pulses that allow the ECM to determine engine speed and top-dead-center TOYOTA Technical Training Knock Sensors Input Sensors Slide 57 214CE04/214CE01/214CE02 Knock Sensors Knock sensors react to the vibrations caused by engine preignition or detonation, and create a voltage signal for the ECM The ECM considers knock sensor signals when controlling ignition timing Most late model vehicles have at least two knock sensors to allow the ECM to better isolate where detonation is occurring Operation Construction The knock sensor contains a piezoelectric element that produces voltage when vibration (pressure) is applied When detonation occurs, the resulting vibrations generate a voltage in the piezoelectric element The more severe the knock, the higher the sensor’s voltage signal There are two types of knock sensors: • Resonance type knock sensors contain a vibration plate that is tuned to respond to a narrow band of vibration frequency This sensor can only detect vibration in this frequency band Resonance type sensors are threaded into engine components such as the block, head, or intake manifold • Flat type knock sensors contain a steel weight capable of responding to a wide range of vibration frequencies Flat type knock sensors are installed over a stud bolt on the cylinder block Toyota Engine Control Systems I Course 852 51 Knock Sensors Input Sensors Slide 58 214CE04/214CE01/214CE02 Diagnosis Below is a summary of typical knock sensor diagnosis Refer to the Repair Manual for specific sensor diagnostic procedures and DVOM test specifications Knock sensor diagnosis usually requires disconnecting the main knock sensor connector and using jumper wires to “swap” the knock sensor location electrically For example, jumper wires are connected so that the ECM sees the Bank sensor as Bank and the Bank sensor as Bank Next, clear the DTCs and operate the engine Check DTC and freeze frame data again If the DTC follows the knock sensor (i.e DTC was for Bank sensor, now DTC is for Bank sensor), then the actual sensor is likely at fault If the DTC does not change, the concern is likely in the wiring or ECM Knock sensors have a specific resistance value that can be checked with a DVOM Refer to the appropriate Repair Manual for knock sensor specifications Fail-safe Position and Torque Pre-ignition 52 A knock sensor problem typically causes the ECM to enter a fail-safe mode in which ignition timing is fully retarded Non-resonant flat type knock sensors are very sensitive to position and torque Always be sure to refer to the Repair Manual for correct sensor orientation and torque specifications Pre-ignition occurs when the air/fuel mixture is ignited before the spark plug event Detonation occurs when a second flame front is ignited due to excessive heat and pressure after the spark plug event TOYOTA Technical Training O2 and A/F Sensors Input Sensors Slide T874f509, T874f310,Slide T874f508 59 Stoichiometry The purpose of oxygen sensors is to help the ECM maintain stoichiometry Stoichiometry is the ratio at which all of the oxygen and all of the fuel in the combustion chamber will balance each other and complete combustion is achieved The ECM makes adjustments to maintain a ratio of 14.7 parts air to part fuel as measured by weight for optimum catalyst performance O2 and A/F Sensors Oxygen sensors help ensure that the air/fuel ratio is correct for optimum catalytic converter efficiency These sensors allow the ECM to adjust the amount of fuel injected and to monitor catalytic converter performance There are many different types of sensors The two most common are the: • Narrow range oxygen sensors, typically called O2 sensors • Wide range oxygen sensors, typically called A/F sensors The type of sensor used before the catalytic converter varies depending on model and model year Refer to the Repair Manual or the underhood emission decal to determine what type of oxygen sensors are used OBD II vehicles require two oxygen sensors: • The sensor before the catalytic converter is sensor (S1) • The sensor after the catalytic converter is sensor (S2) This sensor allows the ECM to determine catalytic converter efficiency On V-type engines, the pre-catalyst sensors are referred to as bank sensor (B1 S1) and bank sensor (B2 S1) The post-catalyst sensors are referred to as bank sensor (B1 S2) and bank sensor (B2 S2) In-line engines can use one or two bank O2 sensors Toyota Engine Control Systems I Course 852 53 O2 Sensor Construction Input Sensors Slide Slide60 T852f081/0140EG56Z/246EG14 T874f509, T874f310, T874f508 O2 Sensor Construction O2 sensors are constructed of zirconia (zirconium dioxide), platinum electrodes, and a heater • The O2 sensor generates a voltage signal based on the amount of oxygen in the exhaust compared to the atmospheric oxygen • The zirconia element has one side exposed to the exhaust stream while the other side is open to the atmosphere • Each side has a platinum electrode attached to the zirconium dioxide element • The platinum electrodes conduct the voltage generated Contamination or corrosion of the platinum electrodes or zirconia elements will reduce the voltage signal output Super Stability O2 Sensor 54 Super Stability O2 sensors are similar to other O2 sensors, with a catalyst layer applied on top of the element coating This catalyst converts the small amount of hydrogen present in the exhaust gas, allowing the sensor to more accurately detect the amount of oxygen For greater accuracy, Super Stability O2 sensor output is measured by impedance The circuit for detecting impedance is inside the ECM Impedance is the effective resistance in an alternating current circuit The impedance of this circuit cannot be accurately measured with an ohmmeter TOYOTA Technical Training O2 Sensor Operation Input Sensors Diagnosis Slide 61 O2 Sensor Operation The O2 sensor generates a voltage signal based on the amount of oxygen in the exhaust compared to atmospheric oxygen: • When exhaust oxygen content is high, O2 sensor voltage output is low • When exhaust oxygen content is low, O2 sensor voltage output is high • During normal operation, the voltage signal cycles from 100 mV to 900 mV The greater the difference in oxygen content between the exhaust stream and atmosphere, the higher the voltage signal From the oxygen content, the ECM can determine if the air/fuel ratio is rich or lean and adjusts the fuel mixture accordingly: • A rich mixture consumes nearly all the oxygen, so the voltage signal is high, in the range of 0.6–1.0 volts • A lean mixture has more available oxygen after combustion than a rich mixture, so the voltage signal is low, 0.4–0.1 volts • At the stoichiometric air/fuel ratio (14.7:1), O2 sensor voltage output is approximately 0.45 volts Toyota Engine Control Systems I Course 852 55 O2 Sensor Limitations Input Sensors Slide Slide62 T874f509, T874f310, T852f083 T874f508 O2 Sensor Limitations Small changes in the air/fuel ratio radically change the O2 sensor’s voltage signal The detection range for this “narrow range” O2 sensor is very small The ECM cannot accurately tell how rich or lean the air/fuel mixture is, so it continuously adds and subtracts fuel, producing a rich/ lean cycle NOTE: Think of the O2 sensor as a switch When the air/fuel ratio passes stoichiometry (14.7:1), the O2 sensor switches either high or low The ECM uses this switching to adjust injection duration The O2 sensor cannot produce an accurate voltage signal until it reaches a minimum operating temperature of 750°F (400°C) It must reach that temperature quickly and stay at that temperature for effective operation 56 TOYOTA Technical Training A/F Sensor Input Sensors Slide Slide63 T852f085/T852f086/0410EG56Z T874f509, T874f310, T874f508 A/F Sensor The A/F sensor looks like an O2 sensor and serves the same purpose, but it is constructed differently and operates differently: • Instead of varying voltage output, the A/F sensor changes the circuit current in relation to the amount of oxygen in the exhaust stream A detection circuit in the ECM uses this to create a voltage signal that varies with the oxygen content of exhaust gases • A/F sensors detect air/fuel ratios over a wider range than O2 sensors, allowing the ECM to more accurately control fuel injection and reduce emissions • A/F sensors operate at temperatures even hotter than O2 sensors, approximately 1200º F (650º C) A/F Sensor Construction A/F sensors may be either conventional (like O2 sensors) or planar type The difference is heater element placement: • Conventional A/F sensors have a central heater element surrounded by the sensor element • Planar type A/F sensors integrate the sensor and heater elements The integrated heater is more efficient, bringing the sensor element to operating temperature more quickly for better sensor performance during engine warm-up Toyota Engine Control Systems I Course 852 57 A/F Sensor Operation Input Sensors Slide 64 A/F Sensor Operation The A/F sensor operates so that there is no current at stoichiometry and the voltage output by the detection circuit is 3.3 volts A rich mixture, which leaves very little oxygen in the exhaust stream, produces a negative current The detection circuit produces a voltage below 3.3 volts A lean mixture, which has more oxygen in the exhaust stream, produces a positive current The detection circuit produces a voltage above 3.3 volts 58 TOYOTA Technical Training Sensor Heaters Input Sensors Slide Slide65 T874f509, T874f310, T852f088/T852f091 T874f508 O2 Sensor Heater To help the O2 sensor reach its operating temperature quickly, the ECM turns on current through a heating element inside the sensor This element heats up as current passes through it The ECM controls the circuit based on engine coolant temperature and engine load (determined from the MAF sensor signal) The O2 sensor heater circuit uses approximately amperes and is generally turned OFF once the engine reaches normal operating temperature A/F Sensor Heater This heater serves the same purpose as the O2 sensor heater, but there are some very important differences A/F sensors require a much higher operating temperature than O2 sensors, so: • Engines using two A/F sensors use an A/F relay (turned ON at the same time as the EFI relay) A relay is required because the A/F sensor heater circuit carries up to 9.9 amperes (versus amperes for O2 sensor heater) to produce the additional heat needed by the A/F sensor • This heater circuit is controlled through pulsewidth modulation (PWM) When cold, the duty ratio is high • The heater may be ON under normal driving conditions to maintain proper A/F sensor operating temperature Toyota Engine Control Systems I Course 852 59 O2 and A/F Sensor Diagnosis Input Sensors Slide Slide66 T874f509, T874f310, T852f350 T874f508 O2 and A/F Sensor Diagnosis A contaminated O2 sensor will not produce the proper signals and will not switch properly Sensors can be contaminated by engine coolant, excessive oil consumption, additives used in sealants, and the wrong additives in gasoline A slightly contaminated sensor may act “lazy,” taking longer to switch from rich to lean This will increase emissions and might affect driveability Many other engine operating conditions can affect the operation of the O2 sensor, such as a vacuum leak, excessive fuel pressure, etc It is also very important that the sensor itself and its heater electrical circuit be in excellent condition Excessive resistance, opens, and shorts to ground will produce false voltage signals Component Test Heater Circuit Test Check the appropriate Repair Manual for detailed procedures for using Techstream to perform basic system tests and DTC-based troubleshooting when O2 or A/F sensor problems are suspected The heater element resistance can be checked with a DVOM The higher the temperature of the heater, the greater the resistance Because the A/F sensor heater circuit carries more current, it is critical that all connections fit properly and have negligible resistance The O2 sensor heater circuit is monitored by the ECM for proper operation If a malfunction is detected, the circuit is turned off This may result in related O2 or A/F sensor DTCs (if the sensor is not warm enough to operate properly) 60 TOYOTA Technical Training ... In-line engines can use one or two bank O2 sensors Toyota Engine Control Systems I Course 852 53 O2 Sensor Construction Input Sensors Slide Slide60 T852f081/0140EG56Z/246EG14 T874f509, T874f310, T874f508... output is approximately 0.45 volts Toyota Engine Control Systems I Course 852 55 O2 Sensor Limitations Input Sensors Slide Slide62 T874f509, T874f310, T852f083 T874f508 O2 Sensor Limitations Small... component speed and/or position Toyota Engine Control Systems I Course 852 47 MRE vs Pickup Coil Input Sensors Slide 53 232CH41 MRE vs Pickup Coil Because engine control MRE sensors use an external