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.

Immobilizer
See Design and Function, Immobilizer.

Fuel pump control module (only vehicles with demand controlled fuel pumps)




The fuel pump control module powers the fuel pump and regulates the output of the pump. The fuel pressure changes with the output of the pump.
The fuel pump control module is supplied with battery voltage by the fuel pump (FP) relay and is grounded in the car body. The fuel pump (FP) relay is controlled by the central electronic module (CEM) when requested by the engine control module (ECM).
The engine cannot be started if the power supply to the fuel pump control module is faulty because the fuel pump will not then be powered.
The fuel pump control module is controlled by the engine control module (ECM) via serial communication. The fuel pump control module then controls the fuel pump by transmitting a PWM voltage on the ground lead for the fuel pump. This means that the voltage drop across the pump changes, and with it the output of the fuel pump. Also see Function, B5244T5, B5254T2 Function.
There are no diagnostics for the fuel pump control module. The engine control module (ECM) has diagnostics for fuel pressure regulation and the associated components. Also see Fuel pressure regulation, diagnostics Fuel Pressure Regulation, Diagnostics.
The pulse-width modulated (PWM) signal from the engine control module (ECM) to the fuel pump control module can be read using VIDA.
The fuel pump control module is on the outside on the right-hand side of the fuel tank.

Fuel pump (only vehicles with demand controlled fuel pumps)




The function of the fuel pump is to ensure that the pressure is correct at the delivery lines for the injectors when requested by the fuel pump control module.
The fuel pump consists of:
1. An electrical pump with an integrated safety valve
2. A pressure equalization valve. This valve equalizes rapid pressure peaks which occur, for example, when the injectors close during engine braking. It also contains a non-return valve which ensures that the pressure in the system does not drop when the engine is switched off
3. Fuel level sensor
4. Fuel filter, cannot be replaced separately
5. Relief valve, releases fuel into the pump housing
6. Ejector pump, continuously fills the pump housing with fuel. The fuel always flows from the fuel pump through the ejector and back to the pump housing.
The fuel pump is supplied with battery voltage by the fuel pump control module and is grounded in the car body.
The engine control module (ECM) has diagnostics for the fuel pump function to ensure that the pressure is correct. Also see Fuel pressure regulation, diagnostics Fuel Pressure Regulation, Diagnostics.
The fuel pump can be activated and its status read off using VIDA.
The pressure in the fuel rail can be measured by connecting a manometer to a nipple. This nipple is on the right-hand end of the fuel rail.

Brake light switch




The task of the brake light 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 brake pedal sensor also disengages cruise control. For further information, see Design and Function, Brake system, design.
The brake light 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 brake light switch. The status of the switch can be read using VIDA.
The brake light 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 information is used by the control module to switch off the cruise control.
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 (position) of the sensor can be read using VIDA.
The sensor is on the pedal box by the clutch pedal.

Air conditioning (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. This is so the engine control module (ECM) can control:
- engine cooling fan (FC) start
- 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. At 0.25 kPa or lower, the voltage is 0 V, at 3100 kPa the voltage is approximately 4.75 V. Low pressure results in low voltage, high pressure in 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)
- 5 cylinder engines have two heated oxygen sensors (HO2S), front and rear
- 6 cylinder engines have four heated oxygen sensors (HO2S), front and rear for bank 1 (cylinders 1-3) and front and rear for bank 2 (cylinders 4-6)
- XC90s with 6 cylinder engines utilize the Y-concept, where the engine has two heated oxygen sensors (HO2S) bank 1 (cyl. 1 -3), bank 2 (cyl. 4 -6) and a rear heated oxygen sensor (HO2S) (bank 1).

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 is so that the Engine Control Module (ECM) 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 uses current regulation 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 needs reference air from the surrounding air. This reference air reaches the heated oxygen sensor via the wiring.

Caution! The wiring 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. For further information, see Heated oxygen sensor (HO2S) diagnostic Heated Oxygen Sensor (HO2S) Diagnostic. VIDA can be used to read off the calculated lambda value from the heated oxygen sensor.

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 beyond 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:
For S60/ S80/ V70/ V70XC/ XC70: Three-way catalytic converter (TWC) diagnostics Three-Way Catalytic Converter (TWC) Diagnostics.
For XC90: Catalytic converter diagnostic 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 wiring 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. 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.
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 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). At 0 °C, the voltage is approximately 4.0 V. At 100 °C the voltage is approximately 0.5 V. Low temperature results in high voltage (high resistance), high temperature 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




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).

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) 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.

Cooling fan for control modules, turbocharger (TC) (certain markets only)




The function of the cooling fan is to cool the control modules in the control module box in the engine compartment. The control modules may be damaged if they overheat.
The engine control module (ECM) activates the fan depending on the signal from the engine coolant temperature (ECT) sensor and the temperature sensor in the control module.
The cooling fan is in the hose between the control module box and the firewall.
The engine control module (ECM) can diagnose the cooling fan. The fan can be activated using VIDA.
A diagnostic trouble code (DTC) is stored if the temperature in the engine control module (ECM) gets too high.

Mass air flow (MAF) sensor (2002-2004)




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
- turbocharger (TC) boost pressure (turbocharged engines only)
- 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 consists of a plastic housing with connectors, test electronics and an aluminum heat sink. The test electronics in the mass air flow (MAF) sensor consist of a hot film comprised of four resistors. The hot film is cooled by the air flow to the engine.
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 1-5 V depending on the air mass. Low air flow (low mass) results in low voltage, high air flow (high mass) gives high voltage. No air flow gives a reading of approximately 1 V.
The mass air flow (MAF) sensor is positioned between the air cleaner (ACL) housing and the intake manifold.
The shape of the mass air flow (MAF) sensor is slightly different on naturally aspirated engines and also contains an air temperature sensor.
The engine control module (ECM) can diagnose the mass air flow (MAF) sensor. The signal can be read using VIDA.

Mass air flow (MAF) sensor (2005-)




The mass air flow (MAF) sensor measures the air mass sucked into the engine. On naturally aspirated engines and 5 cylinder turbocharged engines (except B5254T2/-T4), it also measures the temperature of the intake air.

Air mass
The mass air flow (MAF) sensor 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
- turbocharger (TC) boost pressure (turbocharged engines only)
- 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 consists of a plastic housing with connectors, test electronics and an aluminum heat sink. The test electronics in the mass air flow (MAF) sensor consist of a hot film comprised of four resistors. The hot film is cooled by the air flow to the engine.
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 1-5 V depending on the air mass. Low air flow (low mass) results in low voltage, high air flow (high mass) gives high voltage. No air flow gives a reading of approximately 1 V.

Intake temperature
The temperature sensor detects the temperature of the intake air after the charge air cooler (CAC). This data is used by the engine control module (ECM) to calculate the boost pressure control (turbocharger (TC) and to calculate the 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 V. The lower the temperature the higher the voltage (high resistance). A high temperature results in low voltage (low resistance).
The mass air flow (MAF) sensor is positioned between the air cleaner (ACL) housing and the intake manifold.
The engine control module (ECM) can diagnose the air mass and intake temperature of the mass air flow sensor. The signals can be read using VIDA.

Manifold absolute pressure (MAP) sensor, intake (turbocharged engines only, 2002-2004)




The manifold absolute pressure (MAP) sensor detects the pressure in the intake manifold downstream of the charge air cooler (CAC). The signal from the sensor is primarily used by the engine control module (ECM) to check that the correct boost pressure is reached. The boost pressure is governed by the turbocharger (TC) control valve.
The sensor, which is a piezo resistor, is grounded in the control module and supplied with 5 V from the control module.
The resistance in the sensor changes depending on the pressure in the intake manifold, giving a signal of 0 -5 V. Low pressure results in low voltage, high pressure in high voltage.
The engine control module (ECM) can diagnose the manifold absolute pressure sensor. The sensor signal can be read using VIDA.
The manifold absolute pressure (MAP) sensor is in the intake hose for the throttle body (TB).

Manifold absolute pressure (MAP) sensor, intake (turbocharged engines only, 2005-)




The manifold absolute pressure (MAP) sensor detects the pressure in the intake manifold downstream of the charge air cooler (CAC). On 6 cylinder turbocharged engines and B5254T2/-T4, the temperature of the intake air is also detected.

Pressure sensor
The signal from the sensor is primarily used by the engine control module (ECM) to check that the correct boost pressure is reached. The boost pressure is governed by the turbocharger (TC) control valve.
The sensor, which is a piezo resistor, is grounded in the control module and supplied with 5 V from the control module.
The resistance in the sensor changes depending on the pressure in the intake manifold, giving a signal of 0 -5 V. Low pressure results in low voltage, high pressure in high voltage.

Intake temperature
The temperature sensor detects the temperature of the intake air after the charge air cooler (CAC). This data is used by the engine control module (ECM) to calculate the boost pressure control (turbocharger (TC) and to calculate the 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 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 manifold absolute pressure sensor. The sensor signal can be read using VIDA.
The manifold absolute pressure (MAP) sensor is in the intake hose for the throttle body (TB).

Leak diagnostic unit (certain markets only)




The function of the leak diagnostic unit is to pressurize the fuel tank system during leak diagnostics.
The leak diagnostic unit consists of a plastic housing with:
1. electrical air pump
2. a valve / solenoid which governs the air flow in the unit
3. a heater element (PTC resistor) which warms up the pump.
The electrical pump, valve and heater element in the unit are supplied with voltage by the system relay. The pump, valve and heater element are grounded (control) in the engine control module (ECM).

Note! On model years, 2002-2004 the heating element was controlled by the Central electronic module (CEM), but on request from the Engine control module (ECM).

During leak diagnostics the pump in the leak diagnostic unit starts. The valve in the unit is operated by the engine control module (ECM) by grounding the different circuits internally in the engine control module (ECM).
The Engine control module (ECM) checks the fuel tanks system for leaks by pressurizing the system and at the same time monitoring a number of relevant parameters. Also see: Leak diagnostics (certain markets only) Leak Diagnostics (Certain Markets Only)
The engine control module (ECM) can diagnose the leak diagnostic unit.
The valve in the leak diagnostic unit can be activated.
The leak diagnostic unit is at the upper front edge of the fuel tank.