Evaporative emission (EVAP) system control
EVAP stands for Evaporative Control System. Vapor which evaporates from the fuel in the fuel tank is routed to and stored in the EVAP canister from where it is introduced, at a convenient time, into the combustion process by way of the canister purge (CP) valve using the negative pressure in the intake manifold.
The system consists of
Scheme 113
Fuel tank (1)
To avoid the fuel tank deforming due to negative pressure it has a reinforcement plate screwed to its underside.
Roll-over valve (2)
The roll-over valve is a safety valve which closes if the car tilts sideways by more than 45°, preventing fuel leaking in the event of an accident.
EVAP canister (3)
Fuel vapor from the fuel tank passes a bed of activated charcoal in the EVAP canister. The activated charcoal binds the fuel and pure air flows out into the atmosphere through the vent at the top of the EVAP canister. 80-140 g fuel can be absorbed by the EVAP canister, depending on the volume of charcoal.
Canister purge (CP) valve (4)
The canister purge (CP) valve is located between the EVAP canister and engine intake manifold and fresh air intake. The valve is used to control the flow of fuel vapor from the EVAP canister to the engine. It is connected to a 12 V supply from the main relay and to the engine control module (ECM). The engine control module (ECM) opens the valve by grounding the cable.
Check valves (5)
There are check valves in the hoses between the canister purge (CP) valve and intake manifold and fresh air intake respectively. The check valve in the intake manifold hose prevents air flowing from the engine to the EVAP canister when the turbocharger is operating.
The check valve in the cable to the fresh air intake closes if there is a negative pressure in the intake manifold preventing air flowing from the fresh air intake to the intake manifold.
EVAP canister shut-off valve (6)
Certain markets require the engine control module (ECM) to detect leakages in the tank system, in these markets a leakage diagnostic has been introduced.
In order to check the fuel tank system, cars in these markets have an EVAP canister shut-off valve. This is mounted in front of the left A-pillar, inside the front fender and is connected to the EVAP canister vent. The valve is connected to a 12 V supply from the main relay and can be grounded by the engine control module (ECM). The engine control module (ECM) can close the valve by grounding the cable. The EVAP canister shut-off valve is normally open, it is only closed when the engine control module (ECM) is checking the system.
Control
Normally the canister purge (CP) valve is closed and only opens when the engine control module (ECM) is emptying the canister. When the EVAP canister is emptied the valve is first pulsed, this pulsing increases to bring the mixture from the canister up to a value which varies according to engine load and speed. Because of the pressure in the inlet manifold, fresh air is sucked into the engine through the EVAP canister opening or through the EVAP canister shut-off valve. As the air passes through the EVAP canister, fuel stored in the activated charcoal is drawn into the engine and burned.
When the turbocharger is operating there is a negative pressure in the fresh air intake, this can be used to empty the EVAP canister even when there is an overpressure in the intake manifold.
Scheme 114
The fuel tank holds 73 liters. The filler pipe is routed outside the passenger and cargo compartments, and has a check valve to prevent spillage when refuelling.
The fuel filter is located beside the right hand rear axle mounting bracket, beside the roll-over valve. There is a fuel pressure regulator downstream of the filter. This pressure regulator is mounted behind the engine on the right-hand side above the steering gear. It maintains a pressure of 300 kPa above the pressure in the intake manifold by sending excess fuel back to the fuel tank. Only one fuel line runs from this pressure regulator and pulsation damper to the non-return fuel rail.
A reference air hose runs from the pressure regulator to the intake manifold. There is also a hose to the fresh air intake which sucks moisture out of the pressure regulator.
A vent valve upstream of the filter and a suction connection on the fuel rail are provided to prevent spillage, when replacing the filter for example.
The fuel filter and pump have quick-release connections. Disconnect by pulling the outer connector sleeve to disengage a snap ring on the inside of the connector.
The fuel pump and level sensor are separate units. The level sensor is tubular and its resistance increases by 5 ohms per liter.
Fuel distribution all-wheel drive (AWD)
The fuel tank holds 70 liters. The filler pipe is routed outside the passenger and cargo compartments, and has a check valve to prevent spillage when refuelling.
The fuel tank is saddle shaped with two pontoons connected in the upper part of the fuel tank. There is separate expansion tank above the fuel tank.
The fuel pump (FP) is located at the front of the right pontoon. At the front of the left pontoon is an ejector which pumps fuel to the right pontoon, this ejector unit is driven by the return fuel.
Level indication is provided by two lever sensors connected in series and located on the pump and the ejector unit. Their output signal is the mean of the fuel levels in the two fuel tank pontoons.
The fuel filter is mounted above the rear axle on the right-hand side with the roll-over valve. There is a fuel pressure regulator downstream of the filter.
This pressure regulator is mounted behind the engine on the right-hand side above the steering gear. It maintains a pressure of 300 kPa above the pressure in the intake manifold by sending excess fuel back to the ejector unit in the fuel tank. Only one fuel line runs from this pressure regulator and pulsation damper to the non-return fuel rail.
A reference air hose runs from the pressure regulator to the intake manifold. There is also a hose to the fresh air intake which sucks moisture out of the pressure regulator.
A vent valve upstream of the filter and a suction connection on the fuel rail are provided to prevent spillage, when replacing the filter for example.
The fuel filter, pump and ejector unit are connected with quick-release connectors. To disconnect these press the lower flange into the connector while pulling the hose.
Boost pressure control (BPC) valve
The boost pressure may become excessive if turbine speed is too high. This is prevented by the boost pressure control (BPC) valve (5), which bypasses a proportion of the exhaust gases flowing to the turbine.
Turbocharger (TC) control valve
The boost pressure control (BPC) valve is controlled by boost pressure via the turbocharger (TC) control valve (6). An output on the engine control module (ECM) (7) transmits a pulsed signal to the turbocharger (TC) control valve. By altering the signal duty cycle (the pulsing signal) the pressure to the boost pressure control (BPC) valve can be controlled. When the engine control module (ECM) determines that a higher boost pressure is permissible, the duty cycle of the signal to the turbocharger (TC) control valve is increased and a proportion of the pressure acting on the boost pressure control (BPC) valve pressure servo is allowed through to the turbocharger (TC) inlet. Control pressure is reduced, the boost pressure control (BPC) valve opens later and turbocharger (TC) pressure can increase.
Controlling turbocharger (TC) boost pressure
The turbocharger (TC) control valve duty cycle (pulsed signal) is controlled by a desired value computed by the engine control module (ECM).
To calculate the desired value for the turbocharger (TC) the engine control module (ECM) uses signals from the following sensors
- throttle position (TP) sensor (8)
- mass air flow (MAF) sensor (9)
- engine speed (RPM) sensor (10)
- atmospheric pressure (11).
There is no boost pressure sensor in this turbocharger (TC) system. The engine control module (ECM) uses the mass air flow (MAF) sensor signal (air flow through the air cleaner (ACL)) to calculate boost pressure.
Boost pressure reduction
When the car is driven in 1st or reverse gears the wheels will spin easily if normal turbocharger (TC) control is in operation. To avoid this, boost pressure reduction is engaged at engine speeds under 3,000 rpm and speeds below 10 km/h in first or reverse gears. This applies only to cars with automatic transmission.
The transmission control module (TCM) transmits a signal to the engine control module (ECM) when boost pressure reduction is required. The engine control module (ECM) reduces boost pressure if necessary.
Boost pressure reduction occurs in Winter mode and when the stop (brake) light switch is closed.
Boost pressure can also be reduced to protect the engine from damage. If the knock sensors (KS) detect that the engine is knocking above a given threshold value, and ignition has been retarded and the air/fuel mixture has been enriched, the engine control module (ECM) will reduce the boost pressure until knock ceases.
A reduction in boost pressure also takes place if there is a risk of the engine overheating. If the engine coolant temperature (ECT) sensor indicates that the temperature has exceeded 118°C, the engine control module (ECM) will reduce the boost pressure to reduce heat generation.
Boost pressure increase
At high altitudes the car will not respond well. To compensate for this the duty cycle to the turbocharger (TC) control valve is increased when the car is at high altitudes. The engine control module (ECM) derives height above sea level using the atmospheric pressure sensor.
Boost pressure monitoring
The engine control module (ECM) monitors boost pressure continuously using information supplied by the mass air flow (MAF) sensor describing the intake air mass. If boost pressure exceeds the permissible level, the engine control module (ECM) will close the turbocharger (TC) control valve so that boost pressure is limited to its initial value. If the pressure continues to rise despite this adjustment, the engine control module (ECM) will interrupt the fuel supply by keeping the injectors closed. When pressure has dropped to a permitted level fuel injection is enabled again.
If the computations indicate that the boost pressure is too low, pressure will be limited to its initial value as the fault may be due to a blocked air intake for example.
If a fault occurs in a component that affects the calculation of boost pressure the engine control module (ECM) will only permit initial boost pressure.
Scheme 115
The Assisted air control valve has the task of supplying the air surrounded injectors with air. This results in better volumetric efficiency, more effective combustion and therefore cleaner exhaust emissions. The valve is also used for idle air trim but is also slightly open at higher engine speeds and is then held in standby mode.
Assisted air control valve
The valve is mounted directly on the inlet hose upstream of the throttle (electronic throttle module) and is connected to a hose which via a distributor pipe supplies the air surrounded injectors with air.
The valve has its own driver stage and solenoid and is supplied with 12V. The valve is continuously controlled by the engine control module (ECM) with a variable duty cycle which opens or closes a shutter in the valve.
The valve operates most during a cold start and when idling to minimize Carbon monoxide (CO) and hydrocarbon (HC) emissions while retaining performance and driveability. This depends partially on the fact that the fuel mixed with the air has a smaller droplet size and does not fasten to the intake manifold walls when these are cold and damp. The fuel consumption and warming up period for both the engine and the catalytic converter are also minimized at cold start.
The total calculated amount of air to be introduced into the combustion chamber is divided between the throttle (electronic throttle module) and the Assisted air control valve The input signals to the engine control module (ECM) which affect the control of the Assisted air control valve. throttle position, engine speed (RPM)/position sensor, engine coolant temperature (ECT) sensor, ambient air pressure and ambient air temperature.
Air surrounded injectors
The injectors are installed in the air distribution pipe which is turn mounted inside the intake manifold. The lower section of the injectors have two openings in the sides where air can pass in. When the injector needle begins to lift the openings are exposed and air streams into the center of the injector where the fuel and air are finely dispersed and mixed.
When the needle lifts further the injector nozzle opens and the premixed fuel/air mixture flows into the combustion chamber.
Scheme 116
CAN communication
ECM (Engine Control Module) sends out and receives the following signals via the network
Can and Driver information Module (CDM)
Is the "main computer" in the network and sends on required information to other modules.
It also controls diagnostic communication by connecting the data link connector (DLC) to the network for programming/downloading and reading off diagnostic trouble codes (DTCs) and parameters.
Transmission Control Module (TCM)
The following signals are sent out on the network from the engine control module (ECM) and taken up by the TCM
- Engine load
- Throttle opening
- Acknowledgment of torque limiting
The following signals are sent out on the network from the Transmission Control Module (TCM) and taken up by the ECM
- Torque limiting request stage I and II
- Request to operate the malfunction indicator lamp (MIL)
- Constant idle speed compensation (P/N position) signal
Electronic Throttle Module (ETM)
The following signals are sent out on the network from the electronic throttle module and taken up by the engine control module (ECM)
- Provides information about current throttle position
- Request via engine control module (ECM) to the CAN and Driver module to light the electronic throttle system lamp
- faults discovered in the electronic throttle module are stored as diagnostic trouble codes (DTCs) in the Engine Control Module (ECM)
Anti-lock Braking System (ABS)
The following signals are sent out on the network from the ABS and taken up by the ECM
- Vehicle speed signal, (goes via the CAN and diver module first)
The ABS module continuously sends out the largest differences between the wheel sensor signals on the network, approximately 50 times per second. Using these values the engine control module (ECM) can determine if any misfiring is due to the nature of the road or if there are genuine interruptions in the engine control module. Because of this the accelerometer is not required.
Data Link Connector (DLC)
The request (initiation) when reprogramming and downloading new software takes place via the data link connector (DLC) (pin 7,C-line) to the Can and Driver information Module which closes two internal relays and thereby opens communication with the network.
Serial communication
ECM (Engine Control Module) communicates serially with the following
Immobilizer
The request and exchange of information between the engine control module (ECM) and the Immobilizer.
All serial communication between the data link connector (DLC) and the engine control module (ECM) passes through the Immobilizer control module.
Data Link Connector (DLC)
The serial communication via the data link connector (DLC) (pin 7, C-line) is used for reading off Volvo on-board diagnostic (OBD) system and by the authorities and certain other workshops in the USA/CDN for reading off OBD II codes using the Generic Scan Tool.
Scheme 117
Diagnostics and fault tracing are carried out as before using VIDA.
However from the 1999 model year onwards the Volvo Scan Tool (ST) (which could only communicate serially via the data link connector (DLC)) has been replaced by a new communication unit called the VCT 2000 (Volvo Communication Tool 2000) which can communicate with the modules via the network.
Car communication
The following can be read off during car communication.
Read diagnostic trouble codes (DTCs)
DENSO engine management system contains approximately 120 diagnostic trouble codes (DTC). Each diagnostic trouble code (DTC) can give information on whether the fault depends on an open-circuit, short-circuit to supply voltage or short-circuit to ground. This gives a combined total of 324 different diagnostic trouble codes (DTCs).
Activation
The following output signals/components can be activated
- Injectors (sequentially)
- Power stages/ignition coils (sequentially)
- Assisted air control valve
- air conditioning (A/C) relay (compressor clutch)
- Output signal engine coolant temperature sensor
- Indicator lamp CRUISE
- Heating rear heated oxygen sensor (HO2S)
- Engine cooling fan (FC) (High or low speed)
- Electronic Throttle System warning lamp
- EVAP canister shut-off valve
- Canister purge (CP) valve
- Fuel pump (FP) relay
- Malfunction Indicator Lamp (MIL)
- Econometer signal to the engine control module (ECM)
- Engine speed (RPM) to Can and Driver information Module
Reading off plotter
Here curves and values in a number of parameters van be read off. As before a maximum of 3 can be read at the same time.
Activating diagnostic functions
This is a new function for activating the different test phases in the following on-board diagnostic (OBD) systems
- Return Fuel Lacking System (RFLS)
- Long-term fuel trim (short-term fuel trim) for front heated oxygen sensor (HO2S), idling and part load
Accelerator Pedal Module (APM)
The accelerator pedal module has, for safety reasons, 2 output signals which provide information about requested throttle opening simultaneously
- One analog "Master signal" which is sent to the engine control module (ECM) which in turn requests throttle opening.
- One digital back up signal (Pulse width modulated) which is sent via the engine control module (ECM) to the electronic throttle module and is used when a fault occurs in the analog signal.
The accelerator pedal (AP) position sensor contains 2 potentiometers whose resistance varies with the accelerator pedal (AP) position.
Both are supplied with 5 V using a common cable but are grounded separately.
One signal is analog and goes straight to the engine control module (ECM). The output signal varies between 0.5 V - 4.8 V depending on the accelerator pedal (AP) position.
The other signal (Pulse width modulated) goes first to an analog digital converter where it is digitized and is sent via the engine control module (ECM) to the electronic throttle module.
On cars with automatic transmission the sensor contains a mechanical kick down marker which gives the driver kick down feeling when the pedal is depressed 80% of full depression.
The signal is sent on to the transmission control module (TCM) which then permits the kick down function. There is no longer a separate kick down switch in the sensor, as was the case in earlier versions.
There are several signals which pass through the engine control module (ECM) to continue directly to the electronic throttle module. These are the following signals
- Brake Light Switch is used as a safety switch by the electronic throttle module when a signal is faulty or outside permitted range. If the cruise control is active when the brake light switch is activated, the electronic throttle module will only accept the pulse width modulated signal to control the throttle and disconnect the cruise control.
- Pulse width modulated signal (= duty cycle) is one of the two signals sent from the Accelerator pedal module to the electronic throttle module to control the throttle. The signal is digital and is a back up the ordinary analog signal sent from the Accelerator position module to the engine control module (ECM).
Electronic Throttle Module (ETM)
The electronic throttle module contains a microprocessor has the task of controlling the throttle in response to requests from the engine control module (ECM) but also to diagnose and supervise its own function and if necessary requests the Electronic throttle system warning lamp to be lit, via engine control module (ECM) to the Can driver information module.
The electronic throttle module controls and constantly compares the analog accelerator pedal module signal, sent from the engine control module (ECM) onto the network, with the digital Pulse width modulated signal to determine if the signal from the engine control module (ECM) is within limits.
The engine control module (ECM) can request that the Electronic throttle system warning lamp is lit but the request is transmitted directly to the Can driver module.
The electronic throttle module contains a continuous torque motor which is ungeared and operates directly onto the throttle spindle.
The torque motor is supplied with 12 V and is controlled by the electronic throttle module using signals from the accelerator pedal (AP) position sensor, accelerator pedal module (APM), over requested throttle opening and from both potentiometers about current throttle position.
Both potentiometers are supplied with 5 V and are installed in each end of the throttle spindle.
For safety reasons it has been decided to use 2 potentiometers which each send the same throttle position signal to the electronic throttle module (ETM). With the throttle closed the signal is 0.5 V and at wide open throttle (WOT) approximately 4.5 V.
If one of the potentiometer signals is missing the electronic throttle module can still determine throttle position using the second signal and the car can still drive normally.
The throttle body (TB) mating surfaces are spherical and provides better resolution per degree of opening. This gives more accurate flow control from idling position up to approximately 20% open throttle. The effect is a smoother start at throttle opening/acceleration.
All signal exchange between the engine control module (ECM) and the electronic throttle module is via the network.
Cruise Control
Provides information about the selected speed to the engine control module (ECM) which calculates and requests the throttle angle of the electronic throttle module.
Clutch pedal sensor and brake pedal sensor send signals about clutch or brake pedal depression to disconnect the cruise control and control the throttle.
The brake light switch is an extra safety switch for the brake pedal sensor and travels via the engine control module (ECM) directly to the electronic throttle module.
Electronic throttle system warning lamp
Electronic throttle system has its own warning lamp which lights if there are faults in the components or in the system. Either the engine control module (ECM) or the electronic throttle module can request that the warning lamp is lit.
Fuel trim
Control of the fuel/air mixture occurs using known principles. However the signal from the front probe is of a more linear character. This means that the engine control module (ECM) notices small changes throughout the voltage range and can control the fuel/air mixture much faster and more precisely than before.
Both heated oxygen sensors (HO2S) contain as before a PTC resistor which is supplied with voltage from the engine control module (ECM) in order to reach operating temperature quickly.
If the Engine Control Module (ECM) determines that the ambient air is very cold and damp it may delay starting to heat up the heated oxygen sensors (HO2S) a few seconds. This is to prevent the heated oxygen sensor (HO2S) warm ceramic being touched by cold drops of water and then cracking.
The oxygen sensitive ceramic which measures oxygen levels in the exhaust gases consists of Zirconium dioxide.
Front heated oxygen sensor (HO2S)
Supplied directly after start with 5 V for approximately 30 seconds. After this the engine control module (ECM) lowers voltage to approximately 1V and depending on the oxygen level in the exhaust gases the engine control module (ECM) retains a voltage which is constantly in the region around 0.5V when Lambda = 1.
The output signal characteristic is between 0 - 1V.
Short-term fuel trim control area is very narrow and lies 0.990 and 1.010.
Signal characteristics
- low voltage = rich mixture
- high voltage = lean mixture
| CAUTION | Because the output voltage from the front heated oxygen sensor (HO2S) to the engine control module (ECM) at Lambda = 1 is constantly around 0.5 V it can easily seem as if the fuel trim does not function and that fault-tracing is required. This is correct signal which has a narrow range so that the engine control module (ECM) can control the fuel/air mixture faster and more precisely using the linear output signal from the heated oxygen sensor (HO2S). |
Rear heated oxygen sensor (HO2S)
The heated oxygen sensor (HO2S) operates with the same signal characteristics as previously, but has gained more importance for controlling the fuel/air mixture. The rear heated oxygen sensor (HO2S) has been moved forward nearer to the front heated oxygen sensor (HO2S), just in front of the metal monolith in the catalytic converter.
When the front section of the catalytic converter is first affected by a fault in the fuel/air mixture the rear heated oxygen sensor (HO2S) can sense it sooner and send a signal to the engine control module (ECM) to light the malfunction indicator lamp (MIL) faster. This location also means that the rear heated oxygen sensor (HO2S) warming up time is shorter.
Camshaft Position (CMP) Sensor
The camshaft position (CMP) sensor is a new version and operates using a different signal characteristic to previously.
- The sensor consists of an MRE (Magnetic Resistance Element). It is a permanent magnet with 2 special resistors which are connected in series with each other, where one end is voltage supplied and the other goes to ground. The output signal is an analog sine curve which passes through an analog/digital converter in the camshaft position (CMP) sensor before being sent on to the engine control module (ECM).
- When a tooth on the pulse wheel nears the sensor the magnetic field is bent and affects the resistor located nearest to the ground, resistance affects the voltage and the output signal to the Engine Control Module (ECM) is low. When the same tooth continues past the sensor the magnetic field follows and so affects the other resistor which is located nearest to the voltage supply, this resistor affects the voltage so that the output signal to the Engine Control Module (ECM) is high. The magnetic field swings backwards and forwards between the teeth on the pulse wheel and the engine control module (ECM) senses the signals between the teeth, partly before and partly after the sensor.
- The pulse wheel has 5 teeth where each gap is a different length and corresponds to a particular cylinder. The engine control module (ECM) calculates the time interval from one tooth to the next and can decide exactly which cylinder must be supplied with fuel and spark respectively.
Scheme 118
The system has large similarities with the earlier version in the Motronic 4.4 and is market dependent. Some of the components have a new shape but function according to known principles.
New for DENSO compared to M 4.4
The leak diagnostic occurs only in part load instead of at idling speed.
The fuel tank system now functions with greater negative pressure.
Increased steps and functions in the leak diagnostic.
Temperature gauge
The engine control module (ECM) calculates engine temperature based on signals from the engine coolant temperature (ECT) sensor (4). This information is used for engine management. The information is transmitted to the temperature gauge in the combined instrument panel.
Malfunction indicator lamp (MIL)
The malfunction indicator lamp (MIL) is controlled by the engine control module (ECM). The automatic transmission control module (TCM) can also request that the malfunction indicator lamp (MIL) lights.
The malfunction indicator lamp (MIL) lights when the ignition is switched on but the engine is not running. This indicates that the lamp itself is working.
The malfunction indicator lamp (MIL) lights when the engine control module (ECM) has detected an emission-related fault. The malfunction indicator lamp (MIL) goes out is the engine control module (ECM) senses that the fault has disappeared.
Other output signals
The engine control module (ECM) also transmits signals to the following components
- confirmation of torque limiting by ignition retardation, to the automatic transmission control module (TCM) (4/28)
- engine speed and load signals to the automatic transmission control module (TCM) (4/28)
- throttle angle signal to the automatic transmission control module (TCM) (4/28)
- engine speed (RPM) signal to the combined instrument panel tachometer (5/1)
- engine coolant temperature (ECT) signal to the combined instrument panel (5/1).
- injected fuel quantity to the combined instrument trip computer (5/4)
The malfunction indicator lamp (MIL) lights in the event of misfiring
The malfunction indicator lamp (MIL) lights in the event of misfiring. If there is risk of damage to the three way catalytic converter due to misfiring, the malfunction indicator lamp (MIL) will flash and then switch to a constant light.
The engine control module (ECM) registers and stores the rpm and load parameters within which the misfire occurred. For the diagnostic trouble code (DTC) to be stored, the misfire must occur a further two times within the same rpm and load parameters. The malfunction indicator lamp (MIL) is lit if the diagnostic trouble code (DTC) for misfire is stored in the previous operating cycle and a new diagnostic trouble code (DTC) for misfire is stored in the next operating cycle.
If the misfire stops, the requirements for the rpm and load parameters must be met without misfiring before the engine control module (ECM) will begin counting down to extinguish the warning lamp and erase stored diagnostic trouble codes (DTCs).
Malfunction indicator lamp (MIL) activation
Emissions related diagnostic trouble codes (DTC) are stored even when it is lit. A counter counts down to determine when the malfunction indicator lamp (MIL) should be lit. The conditions for lighting the malfunction indicator lamp (MIL) vary depending on the diagnostic trouble code (DTC) that is stored.
Faults that have been diagnosed in the automatic transmission may affect emissions and the automatic transmission may request the activation of the malfunction indicator lamp (MIL).
ECM (Engine Control Module) sends out and receives the following signals via the network
Can and Driver information Module (CDM)
Is the "main computer" in the network and sends on required information to other modules. It also controls diagnostic communication by connecting the data link connector (DLC) to the network for programming/downloading and reading off diagnostic trouble codes (DTCs) and parameters.
Transmission Control Module (TCM)
The following signals are sent out on the network from the engine control module (ECM) and taken up by the TCM
- Engine load
- Throttle opening
- Acknowledgment of torque limiting
The following signals are sent out on the network from the Transmission Control Module (TCM) and taken up by the ECM
- Torque limiting request stage I and II
- Request to operate the malfunction indicator lamp (MIL)
- Constant idle speed compensation (P/N position) signal
Electronic Throttle Module (ETM)
The following signals are sent out on the network from the electronic throttle module and taken up by the engine control module (ECM)
- Provides information about current throttle position
- Request via engine control module (ECM) to the CAN and Driver module to light the electronic throttle system lamp
- Faults discovered in the electronic throttle module are stored as diagnostic trouble codes (DTCs) in the Engine Control Module (ECM)
Anti-lock Braking System (ABS)
The following signals are sent out on the network from the ABS and taken up by the ECM
- Vehicle speed signal, (goes via the CAN and diver module first)
Data Link Connector (DLC)
When reprogramming and downloading new software and fault-tracing with Volvo on-board diagnostic (OBD) system the initiation request is transferred from VIDA via data link connector (DLC) pin 7 also called C-link Communication link) to the Can and Driver information Module and closing two internal relays and opening communication with the network.
ECM (Engine Control Module) communicates serially with the following
Immobilizer
The request and exchange of information between the engine control module (ECM) and the Immobilizer.
Data Link Connector (DLC)
The serial communication via the data link connector (DLC) (pin 7, C-line) is only used by the authorities and certain other workshops in the USA/CDN for reading off OBD II codes using the Generic Scan Tool.
Scheme 119
General
The engine control module (ECM) continuously controls the Continuous Variable Valve Timing valve which in turn controls the CVVT unit with engine oil pressure.
The Continuous Variable Valve Timing unit is mounted on the exhaust camshaft and is installed on all B52X4T engines. The control has 15 camshaft degrees (30 crankshaft degrees) between its outer positions.
The variable camshaft is hydraulically controlled by the engine oil. The camshaft rotation takes place by the engine oil, using the Continuous Variable Valve Timing valve, transferring to either the Continuous Variable Valve Timing unit front (A) or rear (B) chambers. The chambers are divided by a piston which is fixed in the camshaft. When oil presses on the piston it results in a rotating motion in the piston because it installed in the Continuous Variable Valve Timing unit cover with splines. The pulse wheel for the timing belt is located on the Continuous Variable Valve Timing unit outer cover.
The control is very fast and exact, it only takes approximately 500 ms to transfer between the outer positions.
The Continuous Variable Valve Timing valve has very fine channels, for exact control and is therefore very sensitive to impurities.
The variable camshaft main task is to minimize exhaust emissions, mainly at cold start, but also gives an improved idling quality.
Before the engine starts an internal check occurs as follows
- When the when the ignition is switched on an electrical check is carried out on the signal cable, the power supply cable and the solenoid. The check is carried out for a short-circuit to supply voltage/ground and open-circuit.
- The camshaft checks if it is in the correct position compared to the flywheel, when the camshaft is in its 0-position (mechanical resting position). This can be done by comparing the signals from the camshaft position (CMP) sensor and the engine speed (RPM)/position sensor. If the deviations are too large between these the Continuous Variable Valve Timing valve does not activate and the diagnostic trouble code (DTC) is stored.
- In case of larger controlled deviations at the variable camshaft the time taken to regulate to the control value is measured. This time is used partially to determine how long it takes to alter the camshaft angle and partially to switch off the variable camshaft if the time exceeds a certain maximum time. The camshaft uses the engine oil and oil pressure to turn. The rotation time depends on engine speed (RPM), oil pressure, viscosity etc. which in turn depends on oil temperature and quality etc.
- To check that the camshaft position (CMP) sensor is correct it is compared to the signal from the engine speed (RPM)/position sensor when the engine turns. When the engine has started the check is interrupted. If the check gives faulty values a diagnostic trouble code (DTC) is stored and Continuous Variable Valve Timing control ceases.
Scheme 120
The Continuous Variable Valve Timing valve has three connecting channels and a return channel.
Counted from the front of the valve these are
- Return terminal
- Continuous Variable Valve Timing unit rear chamber terminal
- Engine lubricating system pressure terminal
- Continuous Variable Valve Timing unit front chamber terminal
Inside the Continuous Variable Valve Timing valve there is a piston housing with a spring tensioned piston. The piston housing has three machined grooves with holes drilled into the piston housing center. The piston housing grooves are connected to the Continuous Variable Valve Timing valve three rear connections.
The Continuous Variable Valve Timing valve piston has a channel connecting the pistons front and rear grooves in the center. The piston housing rear groove is connected to the valve return terminal. The front piston groove is wide enough that it can connect one of the piston housing outer groove with the center or stop in a center position where none of the outer grooves are connected.
Scheme 121
In the unemployed position the Continuous Variable Valve Timing valve is in the rear most position (A) because of the valve spring. In this position the piston connects the piston housing center and rear grooves with each other. At the same time the piston has exposed the front piston housing groove so that it is connected to the valve return terminal. Then the oil pressure is guided from the Continuous Variable Valve Timing valve center terminal to the valves rear terminal. From there the pressure is led through the camshaft bearing into the camshaft rear oilway, via the camshaft center channel to the Continuous Variable Valve Timing unit hub. The hub is connected to the Continuous Variable Valve Timing unit front chamber. The pressure in the Continuous Variable Valve Timing unit hub thereby presses onto the Continuous Variable Valve Timing unit piston and presses it backwards.
The piston is rotationally borne, via angle cut splines between the unit hub and cover. The camshaft toothed pulley wheel is installed on the cover and the camshaft is located in the hub. When the piston presses backwards the splines in the unit cover and hub rotate in relation to each other. The arrangement gives a gear ratio giving the piston the possibility of affecting the camshaft a lot with a small movement.
The oil at the rear of the piston is pressed out through the outer hub channels into the camshaft and out through the camshaft upper front oilway The oil is led further through the camshaft bearing, via the front Continuous Variable Valve Timing valve piston housing machining and back to the valve return terminal.
When the Continuous Variable Valve Timing valve receives the signal to move to the other outer position (B) the pressure is led from the piston housing center terminal to the front terminal. The return oil is then sent through the rear piston housing machining to the center of the piston, via the piston rear machining and the piston center channel to the Continuous Variable Valve Timing valve return terminal.
When the desired setting in the chamber is achieved the Continuous Variable Valve Timing valve moves to a central position where none of the terminals are connected with each other. When another camshaft setting in the required the Continuous Variable Valve Timing valve makes a short move in the necessary direction. In this way the Continuous Variable Valve Timing unit can continuously adjust the camshaft.
Scheme 122
Diagnostics and fault tracing are carried out as before using VIDA.
However from the 1999 model year onwards the Volvo Scan Tool (ST) (which could only communicate serially via the data link connector (DLC)) has been replaced by a new communication unit called the VCT 2000 (Volvo Communication Tool 2000) which can communicate with the modules via the network.
The following can be read off during car communication.
Read diagnostic trouble codes (DTCs)
ME 7.0 engine management system contains approximately 135 diagnostic trouble codes (DTC). Each diagnostic trouble code (DTC) can give information on whether the fault depends on an open-circuit, short-circuit to supply voltage or short-circuit to ground. This gives a combined total of 405 different diagnostic trouble codes (DTCs).
Activation
The following output signals/components can be activated
- Injectors (sequentially)
- Power stages/ignition coils (sequentially)
- air conditioning (A/C) relay (compressor clutch)
- Output signal engine coolant temperature sensor
- Indicator lamp CRUISE
- Econometer signal to the Can and Driver information Module
- Engine cooling fan (FC) (High or low speed)
- Electronic Throttle System warning lamp
- EVAP canister shut-off valve
- Turbocharger (TC) control valve
- Canister purge (CP) valve
- Fuel pump (FP) relay
- Malfunction Indicator Lamp (MIL)
- Heating front heated oxygen sensor (HO2S)
- Heating rear heated oxygen sensor (HO2S)
- Continuous Variable Valve Timing (CVVT) camshaft control valve
- Interlock function (starter motor relay), USA/CDN only
Reading off plotter
Here curves and values for approximately 90 parameters can be read off. As before a maximum of 3 can be read at the same time.
Activating diagnostic functions
This is a new function for activating the different test phases in the following on-board diagnostic (OBD) systems
- Return Fuel Lacking System (RFLS)
Control of the fuel/air mixture occurs using known principles. However the signal from the front probe is now of a linear character. This means that the engine control module (ECM) notices small changes throughout the voltage range and can control the fuel/air mixture much faster and more precisely than before.
Both heated oxygen sensors (HO2S) contain as before a PTC resistor which is supplied with voltage from the engine control module (ECM) in order to reach operating temperature quickly.
If the engine control module (ECM) determines that the ambient air is very cold and damp it may delay starting to heat up the heated oxygen sensors (HO2S) a few minutes. This is to prevent the heated oxygen sensor (HO2S) warm ceramic being touched by cold drops of water and then cracking.
The oxygen sensitive ceramic which measures oxygen levels in the exhaust gases consists of Zirconium dioxide.
The output signal characteristic is between 0 - 4.7 V.
The short-term fuel trim control lies between 0.75 and 1.25.
Signal characteristics
- low voltage = rich mixture
- high voltage = lean mixture
The rear heated oxygen sensor (HO2S) operates with the same signal characteristics as previously, but has gained more importance for controlling the fuel/air mixture. The rear heated oxygen sensor (HO2S) has been moved forward nearer to the front heated oxygen sensor (HO2S), just in front of the metal monolith in the catalytic converter.
The camshaft position (CMP) sensor is a new version and operates using a different signal characteristic to previously.
- The sensor consists of an MRE (Magnetic Resistance Element). It is a permanent magnet with 2 special resistors which are connected in series with each other, where one end is voltage supplied and the other goes to ground. The output signal is an analog sine curve which passes through an analog/digital converter in the camshaft position (CMP) sensor before being sent on to the engine control module (ECM).
- When a tooth on the pulse wheel nears the sensor the magnetic field is bent and affects the resistor located nearest to the ground, resistance affects the voltage and the output signal to the Engine Control Module (ECM) is low. When the same tooth continues past the sensor the magnetic field follows and so affects the other resistor which is located nearest to the voltage supply, this resistor affects the voltage so that the output signal to the Engine Control Module (ECM) is high. The magnetic field swings backwards and forwards between the teeth on the pulse wheel and the engine control module (ECM) senses the signals between the teeth, partly before and partly after the sensor.
- The pulse wheel has 4 teeth. The engine control module (ECM) calculates the time interval from one tooth to the next and can decide exactly which cylinder must be supplied with fuel and spark respectively.
Scheme 123
Return Fuel Lacking System
The system has large similarities with the earlier version in the Motronic 4.4 and is market dependent. Some of the components have a new shape but function according to known principles.
When the engine control module (ECM) determines that a higher boost pressure is permissible, the turbocharger (TC) control valve opens further and a proportion of the pressure acting on the boost pressure control (BPC) valve pressure servo is allowed through to the turbocharger (TC) inlet. In this way the control pressure is reduced, the boost pressure control (BPC) valve opens later and turbocharger (TC) pressure can increase.
The engine control module (ECM) affects the turbocharger (TC) control valve by grounding one of the terminals with a fixed frequency where the signals duty cycle determines how much the valve should open and therefore how much the boost pressure can increase.
The charge pressure is reduced when driving in first gear and reverse with engine speed (RPM) below 3000 rpm to reduce the risk of wheel spin. If the engine has an automatic transmission the automatic transmission receives information from the TCM about when reduced charge pressure is required, for example when shifting.
If the car has a manual transmission the Engine Control Module (ECM) determines which gear is selected based on the transmission and final drive gear ratios, engine speed (RPM) and vehicle speed.
On cars with automatic transmission there is also boost pressure reduction in the winter mode.
Boost pressure can also be reduced to protect the engine from damage. If the knock sensors (KS) detect that the engine is knocking above a given threshold value, and ignition has been retarded and the air/fuel mixture has been enriched, the Engine Control Module (ECM) will reduce the boost pressure until knock ceases.
A reduction in boost pressure also takes place If There Is a risk of the engine overheating. If the Engine Coolant Temperature (ECT) sensor indicates that the temperature has exceeded 118°C (244°F), the Engine Control Module (ECM) lowers the boost pressure to reduce heat generation.
Automatic high altitude compensation
Because the Engine Control Module (ECM) determines boost pressure using the signal from the intake air pressure sensor, there is automatic boost pressure control compensation when driving at altitude and in different temperatures. The engine power is not therefore noticeably affected by air density or temperature.
When altitude exceed 2000 meter above sea level the engine control module (ECM) cannot compensate boost pressure any further because the air is too thin.
The Engine Control Module (ECM) constantly monitors boost pressure using the mass air flow (MAF) sensor and the intake air pressure sensor. If boost pressure exceeds permitted levels the Engine Control Module (ECM) shuts the turbocharger (TC) control valve so that the engine torque can only be controlled through limiting the throttle opening. A diagnostic trouble code (DTC) is stored at the same time.
If the calculations display too low boost pressure a diagnostic trouble code is stored.
If a fault occurs in a component that affects boost pressure calculation , the Engine Control Module (ECM) will always limit throttle opening.
If there is a fault in any of the sensors the boost pressure control goes over in an open loop. This means that it is controlled by fixed duty cycle which is a direct function of accelerator pedal (AP) position and engine speed (RPM).
Communication via network
Communication via network
Continuous Variable Valve Timing (CVVT)
Continuous Variable Valve Timing (CVVT)
Continuous Variable Valve Timing (CVVT) valve
Continuous Variable Valve Timing (CVVT) valve
Continuous Variable Valve Timing (CVVT), function
Continuous Variable Valve Timing (CVVT), function
Functions/components controlled
Functions/components controlled
Input signals
Input signals
Return Fuel Lacking System (RFLS)
Return Fuel Lacking System (RFLS)
Turbocharger (TC) control system B52X4T
Turbocharger (TC) control system B52X4T
Communication via network
Continuous Variable Valve Timing (CVVT)
Continuous Variable Valve Timing (CVVT) valve
Continuous Variable Valve Timing (CVVT), function
Functions/components controlled
Input signals
Return Fuel Lacking System (RFLS)
Turbocharger (TC) control system B52X4T