toyota training course t874 engine control systems II ch05

• 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 b

Input Sensors

Section 5

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

Input Sensors

Slide 30

T852f007

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 0 volts The cruise control switch is a typical example of a ground side switch

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 switchPosition 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)

Position and Mode

The ECM adjusts a variety of systems based on temperatures It is critical 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

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 5 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

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 resistanceNote 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

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

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 (non-contact) type For reliability, many late-model sensors create multiple outputs, allowing the ECM to double-check their signals

Slide 37

T852f048/230LX12Position Sensors

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)

Operation — Single Output

Contact Type TPS

Slide 38

T852f049/T852f050/T852f054/T852f055

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 do not provide redundancy

Slide 39

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 do not provide redundancy This electronic sensor is more durable than contact type sensors because

it does not depend on physical contact between components

Operation — Dual Output

Non-Contact Type TPS

Slide 40

230LX12/238EG79

The contact type APPS is mounted on either the throttle body or the accelerator pedal bracket The APPS converts the accelerator pedal movement and position into two electrical signals (APPS produces dual output).

Electrically, the APPS is very similar to the dual output contact type TPS The major difference is that the APPS has two separate voltage supply circuits (VCPA and VCP2) compared to one (VC) on the TPS

Operation — Dual Output

Contact Type APPS

Slide 41

A53752/A54290

The non-contact type APPS is mounted on the accelerator pedal arm Like the non-contact type TPS, it uses Hall ICs and a magnetic yoke to determine the position of the accelerator pedal And, as with the contact type APPS, the only difference between the TPS and APPS is the APPS has two separate voltage supply circuits (VCPA and VCP2) compared to one (VC) on the TPS.

Operation — Dual Output

Non-Contact Type APPS

Slide 42

228TU24/0140EG126C

The first step in position sensor diagnosis should always be to connect the Techstream and observe the Data List while operating the sensor Refer to the Repair Manual for specific sensor operating parameters and specifications.

Check the appropriate Repair Manual for position sensor circuit tests using a DVOM Some ECM connectors are sealed and must not be backprobed Always refer to the specific vehicle Repair Manual for detailed diagnostic instructions, which may include:

• Checking voltage between terminals VC and ground (usually E2) of the ECM connector: This reading confirms that the ECM

is providing the correct voltage You would do this test if you did not measure 5 volts at the VC terminal at the TPS connector If you observe 5 volts at the ECM connector, the problem is in the harness

If you did not observe 5 volts, the ECM may be at fault

Diagnosis with Techstream

Diagnosis with DVOM Checks

Slide 43

T852f057

Many late-model Repair Manuals provide resistance specifications between like terminals of the TPS connector and ECM connector

Disconnect the TPS and ECM connectors and use a DVOM to measure the resistance of the wires between specified terminals These readings will confirm either the integrity of the circuit or an open condition

The resistance of contact type sensors can be checked with a DVOM This method cannot be used on non-contact type sensors.

• Disconnect the sensor connector and move the throttle blade

• Using a DVOM, measure the resistance between each terminal with the sensor at different positions

• Refer to the Repair Manual for specifications

Slide 44

BO1942

Testing (Contact Type Only)

The Mass Air Flow (MAF) sensor converts the volume of air drawn into the engine into a voltage signal This signal significantly impacts the ECM’s calculation of engine load Engine load determines how much fuel to inject, when to ignite the air/fuel mixture, and when to shift the transmission

The MAF sensor is located directly in the intake air stream, between the air cleaner and throttle body

MAF sensors use the “hot wire” principle which depends in part on a temperature sensor, also known as a thermistor, separate from the intake air temperature sensor The MAF sensor contains:

• A thermistor, which changes its resistance in relationship to temperature

• A platinum hot wire

• An electronic control unit

• Intake air temperature (IAT) sensorThe thermistor measures the temperature of incoming air The hot wire is

Mass Air Flow (MAF)

Although the MAF sensor output falls between 0V and 5V, it requires full battery voltage to satisfy the platinum hot wire’s high current draw Battery voltage is supplied to the MAF sensor by the EFI MAIN Relay The MAF sensor has these terminals:

• +B is battery voltage for the MAF sensor

• VG is the MAF sensor signal circuit

• E2G is the MAF sensor ground

The IAT sensor has these terminals:

• THA supplies 5 volts from the ECM through a fixed value resistor

to the IAT sensor

• E2 is the IAT sensor ground

Circuit

Slide 47

A117876E03/A136106E03

MAF sensor diagnosis includes:

• Visual inspection

• Circuit checks

• Component testing

• Operational checkThe MAF sensor must be clean and free of debris to operate properly If the sensor is plugged, the engine will usually start but run poorly or stall This condition may not set a DTC Refer to the Repair Manual for MAF sensor range specifications

As with any sensor, the first step in diagnosis is to check the Data List on the Techstream The MAF sensor reading on the Data List should change when the throttle valve is operated while the engine is running

Check the appropriate Repair Manual for MAF sensor circuit tests using

a DVOM Some ECM connectors are sealed and must not be backprobed Always refer to the specific vehicle Repair Manual for detailed diagnostic instructions, which may include:

Diagnosis with Techstream

Diagnosis with DVOM Checks

Slide 48

T852f068

Position and/or speed sensors provide information to the ECM about the:

• Position of a component

• Rotational speed of a component

• Change in rotational speed of a componentTypical position and speed sensors are:

• Camshaft position sensor/VVT sensor (usually located at the end of the camshaft or on the VVT controller)

• Crankshaft position sensorThese sensors generally use one of two designs:

• Pickup coil (variable reluctance)

• Magnetic resistance element (MRE)

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 do 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)

Operation — Pickup Coil

Type

Slide 51

T852f098/T852f099

Operation — MRE Type

Slide 52

T852f109_v2

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

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

MRE vs

Pickup Coil

Slide 53

232CH41