Part 1

Design

Start control module (SCU)

The start control module (SCU), with its starter button, is the unit that the driver uses to start the vehicle. Also see Design and Function, Immobilizer/start inhibition.
The start control module (SCU) activates the power supply to certain functions in the engine control module (ECM) via fuses in the front integrated relay/fusebox and central electronic module (CEM). The start control module (SCU) also supplies the engine control module (ECM) with start signals.
The start control module (SCU) transmits a high signal (Ubat) to the engine control module (ECM) when the start control module (SCU) is in position III.
The engine control module (ECM) will activate the starter motor relay. In turn the relay activates the starter motor. See also: Function, B8444S Function
The start control module (SCU) is supplied with power from the fuse in the front integrated relay/fusebox.
The central electronic module (CEM) can diagnose the start control module (SCU).

Transmission control module (TCM)
The engine control module (ECM) uses a directly connected signal from the transmission control module (TCM) in the start function (activating the starter motor).

Immobilizer
See Design and Function, Immobilizer/start inhibition.

Alternator control module (ACM)
See Design and Function, Alternator.

Engine speed (rpm) sensor

The engine speed (rpm) sensor provides the engine control module (ECM) with information about the speed and position of the crankshaft. The engine control module (ECM) is able to use the signal from the engine speed (rpm) sensor to determine when a piston is approaching top dead center.
The signal from the engine speed (rpm) sensor is also used to check the engine for misfires. For further information, see: Misfire diagnostic Misfire Diagnostic
The engine speed (RPM) sensor is at the rear of the engine above the flywheel.
The sensor is inductive with a permanent magnet. An alternating current is induced in the sensor when the flywheel/carrier plate passes the engine speed (RPM) sensor. The generated voltage and frequency increases with the engine speed (rpm).
The signal varies between 0.1-100 V depending on the engine speed (rpm).
The Engine Control Module (ECM) is able to determine the engine speed (rpm) by counting the number of holes per time unit. When the reference position passes the engine speed (rpm) sensor, the voltage and frequency drop momentarily to zero, even though the engine is still running. This allows the engine control module (ECM) to determine the position of the crankshaft.
If the signal from the engine speed (rpm) sensor is incorrect or missing, the control module will use signals from the camshaft position (CMP) sensor.
The engine speed sensor can be diagnosed by the engine control module (ECM) and the sensor signal (engine speed) can be read out.

Camshaft position (CMP) sensor

The function of the camshaft position (CMP) sensor is to detect the flanks of the camshaft rotor. The signal from the sensor is used by the engine control module (ECM) to determine the angle of the camshaft.
Each camshaft is divided into a number of flanks (segments) per camshaft revolution. A pulse wheel on the camshaft consisting of teeth (the teeth are positioned by each flank) is used by the camshaft position sensor (CMP) to detect the flanks and the position of the camshaft.
In the event of misfire or engine knock, the control module is able to determine which cylinder is misfiring or knocking using the camshaft position (CMP) sensor's signal. Also see "Design, Knock sensor and Design, Engine speed sensor".
Data about the camshaft position is used during camshaft control (CVVT). See: Function, B8444S Function
The sensor, which is a magnetic resistor with a permanent magnet, is grounded in the control module and supplied with 5 V from the control module. When one of the teeth on the camshaft pulse wheel passes the camshaft position (CMP) sensor, a signal is transmitted to the control module from the camshaft position (CMP) sensor. The signal varies between 0 and 5 V and is high when a tooth is in contact with the camshaft position (CMP) sensor and low when the tooth leaves the camshaft position (CMP) sensor.
There is camshaft position (CMP) sensor for each camshaft.
The camshaft position (CMP) sensors are located by the camshafts on the rear edge of the engine (left-hand side of the vehicle, closest to the flywheel).
The engine control module (ECM) can diagnose the camshaft position (CMP) sensors.

Knock sensor (KS)

The function of the knock sensor (KS) is to monitor combustion knocking from the engine. Knocking may damage the engine and reduces the efficiency of engine combustion.
If the engine control module (ECM) registers knocking from any of the cylinders, the ignition will be retarded for that cylinder at the next combustion stage. If repeated ignition retardation does not prevent knocking, the injection period will be increased. This has a cooling effect.
The sensor is made up of a piezo electrical crystal. If there is engine knock, vibrations (sound waves) spread through the cylinder block to the knock sensor (KS). The resultant mechanical stress in the piezo electrical material in the knock sensors generates a voltage. This signal is transmitted to the Engine Control Module (ECM). The signal corresponds to the frequency and amplitude of the sound waves. This allows the Engine Control Module (ECM) to determine if the engine is knocking. The camshaft position (CMP) sensor and engine speed (rpm) sensor are used to determine the operating cycle of the engine (which cylinder is igniting) and thereby which cylinder is knocking.
The knock sensors are located on the engine block between the cylinder rows.
Knock sensor 1 detects knock on cylinders 5, 6, 7 and 8. Knock sensor 2 detects knock on cylinders 1, 2, 3 and 4.
The engine control module (ECM) can diagnose the knock sensors (KS).

Engine coolant temperature (ECT) sensor

The engine coolant temperature (ECT) sensor checks the temperature of the engine coolant. The temperature of the engine coolant is required so that the engine control module (ECM) can regulate:
- the injection period
- the idle speed
- the engine cooling fan (FC)
- the ignition advance
- engagement and disengagement of the A/C compressor
- diagnostic functions.
The sensor is a negative temperature coefficient (NTC) type which is supplied with power from the control module (signal) and is grounded in the control module.
The resistance in the sensor changes depending on the temperature of the coolant. Depending on the resistance in the sensor, voltage (signal) is transmitted to the engine control module (ECM). The lower the temperature the higher the voltage (high resistance). A high temperature results in low voltage (low resistance).
The engine coolant temperature (ECT) sensor is located beside the thermostat.
The engine temperature sensor can be diagnosed by the engine control module (ECM) and the sensor value can be read out.

Mass air flow (MAF) sensor/Intake air temperature (IAT) sensor

Overview
The mass air flow (MAF) sensor is a combined sensor and contains two sensors in the same component:
- Mass air flow (MAF) sensor
- intake air temperature (IAT) sensor.
The mass air flow (MAF) sensor is positioned between the air cleaner (ACL) housing and the intake manifold.
mass air flow (MAF) sensor
The mass air flow (MAF) sensor gauges the air mass sucked into the engine. It continuously transmits signals to the engine control module (ECM) about the mass of the intake air. This data is used by the engine control module (ECM) to calculate:
- the injection period
- the fuel pressure
- the ignition timing
- the engine load.
The gearbox control module (TCM) also uses this data for its gear shift calculations. This data is transmitted to the gearbox control module (TCM) from the engine control module (ECM) via the high speed side of the Controller area network (CAN).
The mass air flow (MAF) sensor is a hot wire type. Unlike other hot wire types, the mass air flow sensor in the Denso system uses a hot wire which has a ceramic casing. This eliminates the need for a clean burn function.
The mass air flow (MAF) sensor is supplied with battery voltage by the system relay and is grounded in the engine control module (ECM). The signal from the sensor is analog and varies between approximately between 0.5 - 4.5 V. Low air flow (low mass) results in low voltage, high air flow (high mass) gives high voltage.
The mass air flow (MAF) sensor can be diagnosed by the engine control module (ECM) and the sensor signal can be read off.
Intake air temperature (IAT) sensor
The temperature sensor checks the temperature of the intake air in the intake manifold. This data is used by the engine control module (ECM) to calculate injection period. The control module also controls certain diagnostic functions using the signal from the temperature sensor.
The sensor, which is an NTC resistor, is grounded in the control module and supplied with power (signal) from the control module.
The resistance in the sensor changes according to the intake air temperature. This provides the control module with a signal of between 0.5 - 5 V. The lower the temperature the higher the voltage (high resistance). A high temperature results in low voltage (low resistance).
The temperature sensor can be diagnosed by the engine control module (ECM) and the sensor signal can be read off.

Heated oxygen sensors (HO2S)

Front heated oxygen sensor (HO2S)

Caution! The air lines for the heated oxygen sensors (HO2S) must not be trapped or damaged in any way. The connectors for the heated oxygen sensors (HO2S) must not be greased under any circumstances. The oil in the grease would disrupt the reference air and the function of the heated oxygen sensors (HO2S).

The rear heated oxygen sensor (HO2S) is used to provide the Engine Control Module (ECM) with information about the remaining oxygen content of the exhaust gases behind the three-way catalytic converter (TWC). This information is used by the Engine Control Module (ECM) to check the function of the three-way catalytic converter (TWC). This check is carried out when the conditions for the Rear heated oxygen sensors (HO2S) are used to provide the Engine Control Module (ECM) with information about the remaining oxygen content of the exhaust gases behind the three-way catalytic converter (TWC). This information is used by the Engine Control Module (ECM) to check the function of the three-way catalytic converter (TWC). This check is carried out when the conditions for the catalytic converter diagnostics have been met. Rear heated oxygen sensors (HO2S) have no direct effect on regulation of the fuel/air mixture. However the Engine Control Module (ECM) uses the signal to optimize the signal from front heated oxygen sensors (HO2S). For further information, see: Three-way catalytic converter (TWC) diagnostics Three-Way Catalytic Converter (TWC) Diagnostics
The heated oxygen sensor (HO2S) uses voltage control. The signal characteristic is binary. With a binary signal characteristic, the amplitude of the signal curve changes considerably when changing the oxygen content in the exhaust gases. Otherwise its components and function are the same as the front heated oxygen sensor (HO2S).
There are two rear heated oxygen sensors; one for bank 1 and one for bank 2.
Bank 1 (front cylinder row); cylinders 1, 3, 5 and 7.
Bank 2 (rear cylinder row, closest to the passenger compartment); cylinders 2, 4, 6 and 8.
The heated oxygen sensors (HO2S) can be diagnosed by the engine control module (ECM), and signals from them can be read off

Preheating of the heated oxygen sensors (HO2S)
The heated oxygen sensor (HO2S) only functions above a certain temperature, approximately 300 °C. The normal operating temperature is between 300-900 °C. The heated oxygen sensors (HO2S) are electrically pre-heated so that operating temperature is rapidly reached. They are also pre-heated to ensure that the heated oxygen sensors (HO2S) maintain a normal operating temperature and to prevent condensation which could damage the heated oxygen sensor (HO2S).
The heater element in the probe consists of a positive temperature coefficient (PTC) resistor. The system relay supplies the heater element with voltage. The element is grounded in the engine control module (ECM). When the control module grounds the connection a current flows through the PTC resistor. When the heated oxygen sensor (HO2S) is cold, the resistance in the PTC resistor is low and a large current will flow through the circuit. The current from the engine control module (ECM) is pulsed at first to prevent condensation damage to the heated oxygen sensor (HO2S). Depending on the temperature, allowances are made for factors such as the dew point. As the temperature in the PTC resistor rises, the resistance rises, the current falls and switches in stages to a constant current. The pre-heating time for front heated oxygen sensor (HO2S) is short, approximately 20 seconds.
The heater element heats the heated oxygen sensors (HO2S) to approximately 350 °C. The probes maintain this as a minimum temperature. The engine control module (ECM) can diagnose the heater element.

Stop lamp switch

The task of the stop lamp switch is to provide the engine control module (ECM) with information about the position of the brake pedal.
A signal is transmitted to the engine control module (ECM) when the brake pedal is pressed. The engine control module (ECM) disengages the cruise control (if activated). The position of the brake pedal switch (connected to the brake control module (BCM)) also manages the function for switching off cruise control. For further information, see Design and Function, brake control module (BCM).
The stop lamp switch is supplied with power from the start control module (SCU) (terminal 30). When the brake pedal is depressed the switch closes and a high signal (12 V) is transmitted to the engine control module (ECM).
The engine control module (ECM) can diagnose the stop lamp switch. The status (position) of the switch can be read using the diagnostic tool.
The brake light switch is on the pedal box by the brake pedal.

A/C pressure sensor

The air conditioning (A/C) pressure sensor detects the pressure in the high-pressure side of the air conditioning (A/C) system. See also: Function, B8444S Function
The sensor is linear. It is grounded in the control module and supplied with a 5 Volt current from the control module. A linear signal (between 0-5 V depending on the pressure in the air conditioning (A/C)) is transmitted to the control module. Low pressure produces low voltage, high pressure produces high voltage. The air conditioning (A/C) pressure sensor is affected by the pressure in the high-pressure pipe of the air conditioning (A/C) system (narrow pipe).
The engine control module (ECM) can diagnose the air conditioning (A/C) pressure sensor. The sensor value can be read off using the diagnostic tool.

Accelerator pedal (AP) position sensor

The function of the accelerator pedal (AP) position sensor is to provide the engine control module (ECM) and central electronic module (CEM) with information about the position of the accelerator pedal. This data is used by the engine control module (ECM) to deploy the shutter in the throttle unit to the correct angle.
The accelerator pedal (AP) position sensor consists of a plastic housing with two potentiometers, and an Analog/Digital converter. The potentiometers are connected to a common shaft which is affected by the position of the accelerator pedal (AP). The output signals are a pulse width modulated (PWM) signal and an analog signal related to the accelerator pedal (AP) position.
These signals indicate the position of the accelerator pedal (AP). The pulse width modulation (PWM) signal is transmitted to the engine control module (ECM). The analog signal is transmitted to the central electronic module (CEM) and on to the engine control module (ECM) via the controller area network (CAN).
Normally the pulse width modulation (PWM) signal is used to regulate the throttle angle. In the event of a fault in the pulse width modulation (PWM) signal the analog signal is used as a replacement, unless this is also diagnosed as faulty.
The sensor is supplied with 12 V by the system relay via a fuse and is grounded to the body.
The pulse width modulation (PWM) signal is also used in conjunction with the analog signal for accelerator pedal (AP) position sensor diagnostics. The accelerator pedal (AP) position sensor signals can be read using the diagnostic tool. A diagnostic trouble code (DTC) is stored if the engine control module (ECM) detects a difference between the analog and pulse width modulation (PWM) signals. The engine control module (ECM) then uses the signal with the lowest value for regulation.
The accelerator pedal (AP) position sensor is located on the accelerator pedal bracket.

Outside temperature sensor

The function of the outside temperature sensor is to detect the vehicle's ambient temperature. The ambient temperature is required so that the engine control module (ECM) can regulate, among other things:
- the engine cooling fan (FC)
- the air conditioning (A/C) compressor's displacement.
The ambient temperature is also used as a substitute value in the event of a fault in certain components or functions and to control certain diagnostic functions.
The engine control module (ECM) supplies other control modules with the current outside temperature by transmitting information on the controller area network (CAN).
The temperature sensor is a resistor with a negative temperature coefficient, so called NTC type. It is supplied with power from the control module.
The resistance in the sensor changes according to the ambient temperature of the vehicle. This provides the engine control module (ECM) with a signal of between 0-5 V. Low temperature results in high resistance (high voltage). High temperature results in low resistance (low voltage).
The outside temperature sensor is positioned in the left door mirror.
The engine control module (ECM) can diagnose the outside temperature sensor. The sensor value can be read off using the diagnostic tool.