Part 2
Design (Continued)
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.
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 0-5 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. For further information, see Misfire diagnostics 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 6° 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 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.
The following applies to model year 2002 onwards:
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 sensor
The function of the camshaft position (CMP) sensor is to detect the camshaft flanks. The signal from the sensor is used by the engine control module (ECM) to determine the radial position of the camshaft.
Each camshaft has four flanks per camshaft revolution. A pulse wheel on the camshaft consisting of four teeth (the teeth are positioned by each flank) is used by the camshaft position sensor (CMP) to detect the flanks.
The flanks are not symmetric on the camshaft. This allows the control module to determine which flank has been detected and therefore which operating cycle the camshaft is in.
When the operating cycle of the camshaft is established, the control module is able to determine which cylinder should be ignited. In the event of misfire or engine knock, the control module is also able to determine which cylinder is misfiring or knocking. Also see Knock sensor (KS) and Engine speed (RPM) sensor.
Data about the position of the camshaft is used during camshaft control (CVVT). See Function, B5254T2 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 0-1 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 by the controllable camshaft (CVVT).
The engine control module (ECM) can diagnose the camshaft position (CMP) sensor.
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. On turbocharged engines the boost pressure will also be lowered, reducing the engine load.
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).
Electronic throttle unit
The electronic throttle unit, using the control signal from the engine control module (ECM), regulates the amount of air for engine combustion. This is done using an electronic shutter.
The electronic throttle unit consists of a round throttle disc on a shaft. This is turned using a DC motor (damper motor), gear wheel and two springs, an opening spring and a return spring. The damper motor is controlled by the engine control module (ECM) and is supplied with power by an integrated power stage in the control module. At one of the limit positions the throttle disc is closed so that no air can pass the throttle unit. At the other limit position the throttle disc is parallel to the air flow so that the air is able to freely pass through the throttle unit. The throttle disc shaft is mechanically connected to two built-in potentiometers (position sensors) which are supplied with power by the control module. The signals from the potentiometers provide the control module with data about the position of the throttle disc. The electronic throttle unit has a connector with six gold plated pins.
Note! A damaged terminal pin surface can interfere with the function
1. Current channels, potentiometers
2. Contact strips, potentiometers
3. Spring
4. Spring
5. Throttle disc
6. Damper motor
7. Gear wheel
8. Gear sector
9. Connector.
The electronic throttle unit is located on the engine intake manifold.
In the event of a fault, the throttle unit must be replaced as a single unit.
The engine control module (ECM) can diagnose the electronic throttle unit.
Throttle position (TP) sensor
See Electronic throttle unit.
Accelerator pedal (AP) position sensor
The function of the accelerator pedal (AP) position sensor is to provide the engine control module (ECM) with information about the position of the accelerator pedal. This data is used by the control module to deploy the shutter in the throttle unit to the correct angle.
The sensor consists of a plastic housing with two potentiometers, an Analog/Digital converter and circuits. The potentiometers are connected to a shaft which is affected by the position of the accelerator pedal (AP). The resistance in the potentiometers changes with the position of the accelerator pedal (AP).
The accelerator pedal (AP) position sensor transmits an analogue and a digital signal (pulse width modulated (PWM) signal) to the control module. These signals indicate the position of the accelerator pedal (AP). The digital signal is generated by the sensors Analog/Digital converter.
The analog and digital signals are used at the same time by the control module to regulate the throttle shutter angle.
The sensor is supplied with 12 V by the system relay via a fuse and is grounded to the body.
The digital signal is also used in conjunction with the analog signal for accelerator pedal position sensor diagnostics. The accelerator pedal (AP) position sensor signals can be read off using VIDA. A diagnostic trouble code (DTC) is stored if the engine control module (ECM) detects a difference between the analog and digital signals. The engine control module (ECM) then uses a minimal value to ensure the function (limp home).
The accelerator pedal (AP) position sensor is located on the accelerator pedal bracket.
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 following applies from model year 2005-
The signal of the engine coolant level sensor can be read using VIDA.
The engine control module (ECM) cannot diagnose the engine coolant level sensor.