System Components - Part 1
DESIGN
Ignition switch
The Engine Control Module (ECM) uses the signal from the ignition switch to detect when the ignition key has been turned to position II or III. When the key is in the ignition position (position II) or starting position (position III) a high signal (Ubat) is transmitted from the ignition switch to the engine control module (ECM). The engine management system prepares for start-up (for example, temporarily activates the fuel pump (FP) relay). When the flywheel in the engine rotates, the engine speed (RPM) sensor signal is used to keep the fuel pump (FP) relay activated. The fuse in the fusebox in the passenger compartment supplies current to the ignition switch. The central electronic module (CEM) can diagnose the ignition switch.
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.
The information is used to switch off the cruise control. In the event of a fault with the electronically controlled throttle system the engine speed (RPM) can not be affected by the accelerator pedal (AP) when the brake pedal is depressed.
The stop lamp switch signal is also used to diagnose the brake pedal position sensor. From model year 2002 the brake pedal position sensor is directly connected to the brake control module (BCM). The brake pedal position sensor was previously directly connected to the engine control module (ECM). The stop lamp switch is supplied with power from the ignition switch (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 of the switch can be read using VIDA.
The stop lamp switch is on the pedal box by the brake pedal.
Clutch pedal sensor (manual transmissions only)
The clutch pedal sensor provides the Engine Control Module (ECM) with information about the position of the clutch pedal.
This data is used by the control module to disengage the cruise control and regulate the throttle depending on the position of the clutch pedal. The sensor signal is also used by the control module to prevent engine start if the clutch pedal is not pressed (certain markets).
The sensor consists of a sliding potentiometer which is supplied with power by the control module (signal) and which is grounded in the control module.
The resistance in the sensor drops when the clutch pedal is pressed.
The Engine Control Module (ECM) can diagnose the clutch pedal sensor. The status of the switch can be read using VIDA.
The sensor is on the pedal box by the clutch pedal.
Air conditioning (A/C) compressor
The air conditioning (A/C) pressure sensor detects the pressure in the high-pressure side of the air conditioning (A/C) system. This is so the engine control module (ECM) can control:
start-up of the engine cooling fan (FC) step 2
start-up of the engine cooling fan (FC) step 3
stopping the compressor if the pressure in the air conditioning (A/C) is too high
constant idle speed compensation for the air conditioning (A/C) compressor load.
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 engine control module (ECM) can diagnose the air conditioning (A/C) pressure sensor. The sensor value can be read off using VIDA.
The air conditioning (A/C) pressure sensor is positioned on the high pressure delivery line for the air conditioning (A/C) system.
Heated oxygen sensors (HO2S)
Front heated oxygen sensor (HO2S)
The front heated oxygen sensor (HO2S) is used to provide the engine control module (ECM) with information about the remaining oxygen content of the exhaust gases in front of the three-way catalytic converter (TWC). This information is used by the engine control module (ECM) so that it can continually check the combustion so that lambda=1. lambda=1 is the ideal fuel-air ratio, with 14.7 kg air/1 kg fuel. The heated oxygen sensor (HO2S) uses current control and its signal characteristic is linear. With a linear signal characteristic, the amplitude of the signal curve is low when changing the oxygen content in the exhaust gases. The probe consists of a preheating element (see "Pre-heating heated oxygen sensors (HO2S)") and the actual lambda sensor. The lambda sensor is an oxygen sensitive ceramic body consisting of zirconium oxide. The control module supplies power to the ceramic body, which reacts to the oxygen content of the exhaust gases. This in turn affects the signal to the Engine Control Module (ECM). In order to determine the oxygen content in the exhaust pipe, the heated oxygen sensor (HO2S) needs reference air from the surrounding air. This reference air reaches the heated oxygen sensor (HO2S) via the cable harness.
Caution! The cable harness 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 engine control module (ECM) can diagnose the heated oxygen sensor (HO2S). For further information, see Heated oxygen sensor (HO2S) diagnostic. VIDA can be used to read off the calculated lambda value from the heated oxygen sensor (HO2S).
Rear heated oxygen sensor (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 catalytic converter diagnostics have been met. The rear heated oxygen sensor (HO2S) has no direct effect on regulation of the fuel/air mixture. However the Engine Control Module (ECM) uses the signal to optimize the signal from the front heated oxygen sensor (HO2S). For further information, see Catalytic converter diagnostic.
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).
Caution! The cable harness 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 engine control module (ECM) can diagnose the rear heated oxygen sensor (HO2S). The signal can be read using VIDA.
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. This also ensures 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 the front heated oxygen sensor (HO2S) is short, approximately 20 seconds. The rear short-term fuel trim takes longer to warm up. This is to prevent damage to the probe. The pre-heating time for the front heated oxygen sensor (HO2S) is short, approximately 20 seconds.
Probe preheating begins as soon as the engine is started. 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.
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 according to the temperature of the engine coolant. This provides the control module with a signal of between 0.1-4.9 V. 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 control module (ECM) can diagnose the engine coolant temperature (ECT) sensor. The sensor value can be read off using VIDA.
Engine cooling fan (FC)/engine cooling fan (FC) control module
The engine cooling fan (FC) has two functions. One is to cool the engine compartment, the other is to cool the condenser when the air conditioning (A/C) compressor is working.
The engine control module (ECM) transmits a pulse width modulated (PWM) signal to the engine cooling fan (FC) control module. The control module then activates the fan at one of three different speeds. The speed of the engine cooling fan (FC) is determined by the engine control module (ECM), depending on the coolant temperature (based on the signal from the engine coolant temperature (ECT) sensor) and the vehicle speed.
When the vehicle is stationary, the engine cooling fan (FC) is activated as follows:
the first stage is activated at approximately 105°C and shut of at approximately 100°C
the second stage is activated at approximately 110°C and shut of at approximately 105°C
the third stage is activated at approximately 115°C and shut of at approximately 110°C.
Warning! The engine cooling fan (FC) may start itself for some time after the engine has been switched off. This is normal.
The engine cooling fan (FC) and its control module are behind the radiator.
The engine control module (ECM) can diagnose the engine cooling fan (FC). The fan can be activated using VIDA.
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 ignition timing
the engine load.
The transmission control module (TCM) also uses this data for its gear shift calculations. This data is transmitted to the transmission 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 0.5-4.5 V depending on the air mass. Low air flow (low mass) results in low voltage, high air flow (high mass) gives high voltage.
The mass air flow (MAF) sensor is positioned between the air cleaner (ACL) housing and the intake manifold.
The mass air flow (MAF) sensor also contains an intake air temperature (IAT) sensor.
The engine control module (ECM) can diagnose the mass air flow (MAF) sensor. The signal can be read using VIDA.
Outside temperature sensor
The outside temperature sensor detects the temperature in the surrounding air. The signal is used by the engine control module (ECM) as a substitute value in the event of a fault in certain components or functions and to control certain 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, which provides a signal between 0.14.7 V, changes depending on the outside temperature. Low temperatures produce high voltage (high resistance), high temperatures produce low voltage (low resistance).
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 VIDA.
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 (TDC). However it is unable to use the signal from the engine speed (RPM) sensor to determine whether the piston is in the combustion stroke or whether the exhaust valve is open (exhaust stroke). The signal from the camshaft position (CMP) sensor is also required to determine the operating cycle of the engine. The signal from the engine speed (RPM) sensor is also used to check the engine for misfires (misfire diagnostics).
Cars with manual transmissions have a series of holes drilled in the periphery of the flywheel. Cars with automatic transmissions have a steel ring with punched holes. This steel ring is welded to the edge of the carrier plate. In both cases, there is ~ between each hole. This arrangement creates a hole for each tooth. There are 360° in one revolution. 6° between each hole means that there are 60 holes. However one hole is not drilled/punched, to create a reference position (tooth) for the crankshaft. This reference position is 72° before the top dead center (TDC) of cylinder 1 on a 5 cylinder engine.
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 (AC) 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 tooth 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 the signals from the camshaft position (CMP) sensor, on the condition that the position of the camshaft has been adapted and the car can be driven if there is no signal.
The engine control module (ECM) can diagnose the engine speed (RPM) sensor. The sensor value (engine speed (rpm)) can be read off using VIDA.
Camshaft position (CMP) sensor
The Engine Control Module (ECM) uses the signals from the camshaft position (CMP) sensor and the engine speed (RPM) sensor to establish the operating cycle of the engine. This enables the engine control module (ECM) to:
start the engine more quickly
control the correct ignition coil and injector function as a substitute for the engine speed (RPM) sensor
check the camshaft continuous variable valve timing (CVVT).
The pulse wheel on the camshaft has five teeth with different gaps which correspond to a specific cylinder. For further information, also see Knock sensor (KS), Engine speed (RPM) sensor and Function The sensor, which is a magnetic resistor with a permanent magnet, is grounded in the control module and supplied with current 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 0-1 V and is low when a flank passes the camshaft position (CMP) sensor.
The camshaft position (CMP) sensor is positioned at the rear of the engine on the camshaft with continuous variable valve timing (CVVT). The engine control module (ECM) can diagnose the camshaft position (CMP) sensor.
Knock sensor (KS)
Cars of model year 1999-2000 have a knock sensor. Cars from model year 2001 are equipped with two knock sensors (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 (KS) are positioned on the cylinder block below the intake manifold. The engine control module (ECM) can diagnose the knock sensors (KS).
Engine coolant level sensor
The function of the engine coolant level sensor is to alert the driver if the engine coolant level in the expansion tank is too low.
The sensor is a magnetic reed switch, which is enclosed in a pipe on the bottom of the expansion tank. Around the pipe, on the inside of the expansion tank is a float. This float contains a magnet. When the engine coolant level is above minimum, the float is too high in the tank to affect the switch. However if the engine coolant level falls below the minimum level, the magnetic field acts on the switch. The sensor is supplied with voltage (signal) from the Engine Control Module (ECM) and grounded in chassis. When the engine coolant level in the expansion tank is over a certain level the circuit closes, which produces a low signal. When the engine coolant level is below a certain level the circuit is opened by the engine coolant level sensor, which produces a high signal. When the engine control module (ECM) detects a high signal the information about low engine coolant level is transmitted via the Controller area network (CAN) to the driver information module (DIM), which warns the driver.
Note! There are no functions controlled by the engine which are directly connected to the low coolant level warning lamp. The Engine Control Module (ECM) only transfers the signal which is used by the Driver Information Module (DIM).
The engine control module (ECM) cannot diagnose the engine coolant level sensor.