Design [2 of 4]
Rear heated oxygen sensor (HO2S)
Caution! The air lines for the heated oxygen sensors must not be trapped or damaged in any way. The connectors for the heated oxygen sensors 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.
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 more 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).
Caution! The air lines for the heated oxygen sensors must not be trapped or damaged in any way. The connectors for the heated oxygen sensors 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.
The engine control module (ECM) can diagnose the rear heated oxygen sensor. 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. 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 the 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.
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, a 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 control module (ECM) can diagnose the engine coolant temperature sensor. The sensor value can be read off using VIDA.
Engine cooling fan (FC) / engine cooling fan (FC) control module
Note! The engine cooling fan may have a post-run of up to approx. 6 minutes after the engine has been turned off. The time for the fan's post-run depends on engine temperature, temperature in the engine compartment and pressure level in the AC-system.
Warning! Be careful since the engine cooling fan may have a post-run after the engine has been turned off.
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 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.
The temperature conditions for engagement of the different engine cooling fan (FC) stages may vary slightly, depending on the engine variant and the equipment level. The temperature conditions apply when:
- the A/C is off
- no faults are detected by the Engine Control Module (ECM).
Warning! Be careful since the engine cooling fan may have a post-run after the engine has been turned off.
The engine cooling fan (FC) and its control module are behind the radiator.
The engine control module (ECM) can diagnose the engine cooling fan. The fan can be activated using VIDA.
Mass air flow sensor
Overview
The mass air flow (MAF) sensor on naturally aspirated engines is a combined sensor and contains two sensors in the same component:
- mass air flow (MAF) sensor
- temperature sensor.
The mass air flow (MAF) sensor is positioned between the air cleaner (ACL) housing and the intake manifold.
Mass air flow 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 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 analogue and varies between approximately 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.
On turbocharged engines the mass air flow (MAF) sensor has a slightly different design. It is not a combined sensor and only contains sensors for the mass air flow.
The engine control module (ECM) can diagnose the mass air flow (MAF) sensor. The signal can be read using VIDA.
Temperature 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 temperature of the intake air. 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 engine control module (ECM) can diagnose the temperature sensor. The sensor signal can be read using VIDA.