The Engine Control Module (ECM) monitors the conditions required for optimum combustion of fuel in the cylinder through sensors located at strategic points around the engine. From these sensor inputs, the engine control module can adjust the fuel quantity and timing of the fuel being delivered to the cylinders. The ECM also controls the valve period, by driving the variable valve control (VVC) mechanism, to produce the optimum engine torque characteristic.
The main features are as follows:
- A single ECM controls the fuel injection system and the ignition system. The ECM incorporates short circuit protection and can store intermittent faults on certain inputs. TestBook can interrogate the ECM for these stored faults.
- ; The ECM measures the cam period via the cam sensor, and controls the VVC mechanism via two solenoids: one which increases the cam period and one which reduces it.
- The ECM is electronically immobilised preventing the engine from being started unless it receives a coded signal from the anti-theft control unit.
- The ECM uses the speed/density method of air flow measurement to calculate fuel delivery. This method calculates the density of intake air by measuring its pressure and temperature. The density signal, along with engine speed, allows the ECM to make a calculation of the air volume being inducted, and hence determine how much fuel should be injected to give the correct air/ fuel ratio.
- A separate diagnostic connector allows engine tuning or fault diagnosis to be carried out using TestBook without disconnecting the ECM harness multiplug. The multiplug is located on the passenger compartment fusebox.
- The ECM harness multiplug incorporates specially plated pins to minimise oxidation and give improved reliability.
- The ECM controls the operation of the radiator, air conditioning and engine compartment fans based on signals received from engine coolant temperature and engine bay temperature sensors. If a high engine temperature is detected, the ECM will prevent the air conditioning system from operating.
- If certain system inputs fail, the ECM implements a back-up facility to enable the system to continue functioning, although at a reduced level of performance.
- The ECM used on the VVC engine implements tune select. This means that each ECM may contain one or more vehicle’s engine calibration. When first supplied, the ECM has no calibration selected and will not run the engine. When fitted to a vehicle, the ECM calibration for that vehicle must be selected using TestBook. This is to prevent ECM’s being fitted to vehicles with the wrong calibration selected. It is an additional action to programming the ECM security code.
The engine control module determines the optimum ignition timing based on the signals from the following sensors:
1. Crankshaft position sensor - Engine speed and crankshaft position
2. Camshaft position sensor - Camshaft position
3. Manifold absolute pressure sensor - Engine load
4. Engine coolant temperature sensor - Engine temperature
5. Throttle position sensor - Throttle pedal position
The VVC engine employs a direct ignition system which consists of two twin-ignition coils driven directly from the ECM. Each twin-ignition coil supplies two cylinders.

Crankshaft position sensor
The speed and position of the engine is detected by the crankshaft position sensor which is bolted to, and projects through, the engine adapter plate adjacent to the flywheel. The crankshaft position sensor is an inductive sensor consisting of a bracket mounted body containing a coil and a permanent magnet which provides a magnetic field. The sensor is situated such that an air gap exists between it and the flywheel. Air gap distance is critical for correct operation. The flywheel incorporates a reluctor ring which consists of 32 poles spaced at 10 intervals, with 4 missing poles at 30 ,60 , 210 and 250 . When the flywheel rotates, as a pole passes the CKP sensor, it disturbs the magnetic field, inducing a voltage pulse in the coil, which is transmitted to the ECM. By calculating the number of pulses that occur within a given time, the ECM can determine the engine speed. The output from this sensor when used in conjunction with that from the manifold absolute pressure sensor provides idle stabilisation and reference for both ignition and injection timing. Camshaft position sensor The camshaft position sensor has two functions. The first is to enable the ECM to run a sequential fuelling mode. The second is to measure the actual cam period, this measurement is achieved using teeth on the camshafts to indicate when the valve opens and closes. If the camshaft position sensor fails when the engine is running, the engine will continue to run normally in sequential fuelling mode. If the sensor fails before the engine is started, the engine will start but run in grouped fuelling mode. The engine running in grouped fuelling mode can be detected by a reduced rev limit: 5500/5800 rpm in comparison to the normal rev limit of 7000/7300 rpm. Camshaft position sensor failure can be identified using TestBook.

Manifold absolute pressure sensor
The manifold absolute pressure (MAP) sensor is fixed directly to the inlet manifold. The ECM provides a 5 volt supply and earth path to the sensor. The sensor then returns a voltage output which represents the pressure. Increases and decreases in the manifold pressure provide the ECM with an accurate representation of the load being placed on the engine. Allowing the ECM to calculate both the ignition timing and quantity of fuel to be injected to achieve optimum fuelling of the engine. The voltage supply for this sensor is provided directly from the ECM.
Engine coolant temperature sensor
The engine coolant temperature sensor is a ’thermistor’ (a temperature dependent resistor), i.e. the voltage output varies in proportion to temperature. The sensor is located in the front of the coolant outlet elbow. The ECM constantly monitors this signal and uses the information to provide optimum driveability and emissions by advancing or retarding the ignition timing.
Idle speed control
With the throttle pedal released and the engine at idle, the ECM uses the fast response of the engine ignition timing to maintain idle stabilisation. When loads are placed on or removed from the engine, the ECM senses the change in engine speed and in conjunction with adjusting the idle air control valve, advances or retards the ignition timing to maintain a specified idle speed. When load is removed from the engine, the idle air control valve returns to its original position and the ignition timing returns to the idle setting. NOTE: Due to the sensitivity of this system, the ignition timing will be constantly changing at idle speed.

Ignition coil
The coils for the programmed ignition system are mounted on the rear face of the engine block. Each coil has a low primary winding resistance (0.71 to 0.81 ohms at 20 C). This allows the full h.t. output to be reached faster and so makes the coil operation more consistent throughout the engine speed range.
Hydraulic control solenoid
The ECM controls two solenoids in order to control the VVC mechanism. Only one solenoid will be energised at a time to either drive the VVC mechanism towards minimum cam period, or towards maximum cam period. The desired cam period is calculated by the ECM using engine speed and manifold pressure (engine load). The current cam period is measured by the ECM using the camshaft position sensor. The ECM then energises the correct solenoid in order to move the mechanism towards the desired position.
Oil Temperature sensor
An oil temperature sensor is mounted in the hydraulic control unit (HCU). The oil temperature measured by the ECM is used to derive the viscosity of the oil passing through the HCU which indicates how quickly the VVC mechanism will respond.
If the ECM detects any faults with cam period measurement during start up and initial running, the ECM will try and drive the mechanism to minimum cam period. If the ECM loses the cam period signal during running, the cam period will remain frozen at the last valid period. Engine speed may be limited as low as 5500 rpm depending on cam period when the fault occurred. The engine idle speed will be raised and will remain raised for the rest of the journey.
NOTE: A camshaft period measurement fault will only be recorded by the ECM if the fault is detected at start-up or during initial running. Camshaft period measurement faults are identified using TestBook.
Engine Control Module (ECM)

The Modular Engine Management System (MEMS) is controlled by an ECM mounted on the bulkhead in the engine compartment. The ECM is an adaptive unit which over a period of time learns the load and wear characteristics of the engine. requirements when the engine is running at normal operating temperature:
1. The position of the idle air control valve required to achieve a specified idle speed. This is then used as a reference for idle air control valve movement to achieve idle speed under all load conditions.
2. The fuelling change or offset required to achieve an oxygen sensor output indicating an air-fuel ratio of 14.7:1. This allows the system to provide the correct fuelling without having to apply excessive adjustments to the fuelling which can adversely affect the emissions and driveability.
NOTE: After fitting a different ECM, TestBook will be required to reprogram the ECM with the code from the anti-theft control unit; to select the correct vehicle tune, and to perform a full engine tune procedure. The ECM inputs and outputs are shown in the following table.

Crankshaft position sensor VVC solenoids
Camshaft position sensor Ignition coils
Manifold absolute pressure sensor Injectors
Engine oil temperature Purge valve
Engine coolant temperature sensor Idle air control valve
Intake air temperature sensor Fuel pump relay
Heated oxygen sensor ECM Diagnostic connector
Throttle position sensor Heated oxygen sensor relay
Diagnostic input Main relay
Battery supply Cooling fans
Starter signal Air conditioning
Earth supply Engine bay cooling fan relay
Anti-theft control unit Engine bay warning lamp relay
Engine bay temperature sensor

Intake air temperature sensor
The intake air temperature sensor is located in the side of the inlet manifold. The sensor is of the negative temperature coefficient (NTC) type, designed to reduce its resistance with increasing temperature. The ECM receives a signal from the IAT sensor proportional to the temperature of the intake air. When this signal is used in conjunction with the signal from the manifold absolute pressure sensor. The ECM calculates the volume of oxygen in the air and adjusts the quantity of fuel being injected, to achieve optimum fuelling of the engine. Injectors The four fuel injectors are fitted between the pressurised fuel rail and inlet manifold. Each injector comprises of a solenoid operated needle valve and a specially designed nozzle to ensure good fuel atomisation. After the engine has started the injectors are controlled individually. The ECM determines when to operate the injectors based on the signal it receives from the crankshaft and camshaft position sensors. injectors are required to be open, the injector solenoids are energised and fuel is sprayed into the inlet manifold onto the back of the inlet valves. The ECM carefully meters the amount of fuel injected by adjusting the injector opening period (pulse width). During cranking, when the engine speed is below approximately 400 rev/min, the ECM increases the injector pulse width to aid starting. The amount of increase depends upon engine coolant temperature. To prevent flooding, the ECM periodically inhibits the operation of the injectors during extended cranking. Throttle housing
The throttle housing is located between the inlet manifold and air intake hose and is sealed to the manifold by an ’O’ ring. The throttle housing incorporates a throttle disc which is connected to the throttle pedal via the throttle lever and a cable. There are two breather pipes connected to the throttle housing, one either side of the throttle disc. When the engine is running with the throttle disc open, both pipes are subject to manifold depression and draw crankcase fumes into the manifold. When the throttle disc is closed, only the pipe on the inlet manifold side of the disc is subject to manifold depression. This pipe incorporates a restrictor to prevent engine oil being drawn into the engine by the substantially greater manifold depression. The throttle body also houses the throttle position sensor which provides signals to the ECM relative to the throttle disc position and rate of movement.

Throttle position sensor
The throttle position (TP) sensor is a potentiometer attached to the throttle housing and is directly coupled to the throttle disc, the TP sensor is non adjustable. The TP sensor is used to detect closed throttle, allowing the ECM to initiate idle speed control. The ECM supplies the TP sensor with a 5 volt feed and an earth path. The TP sensor returns a signal proportional to throttle disc position. Throttle disc movement causes voltage across the TP sensor to vary. The control module calculates the rate of change of the voltage signal in positive (acceleration) or negative (deceleration) directions. From this, the ECM can determine the rate of movement and apply acceleration enrichment, deceleration fuel metering or over-run fuel cut-off.
Idle air control valve
The idle air control valve is mounted on the inlet manifold and controlled by the ECM. The idle air control valve opens a pintle valve situated in an air passage in the throttle housing. Air is allowed to bypass the throttle disc and flow straight into the inlet manifold. By changing the amount the idle air control valve is open the ECM can control engine idle speed and cold start air flow requirements by adjusting the flow of air in the passage. During cold starting the ECM indexes the idle air control valve open slightly to provide a level of fast idle, dependent on engine coolant temperature. As the engine warms, fast idle is gradually decreased until normal operating temperature is reached. The position of the idle air control valve should be within the range of 20 to 40 steps when the engine is idling at normal engine temperature. This ensures that the idle air control valve is able to supply varying amounts of by-pass air to compensate for all loads and temperature conditions. If the valve is identified as being outside the specified range a fault may exist. Faults should be investigated and rectified before using TestBook to adjust the idle air control valve.

Engine management relay module
The relay module is located on the bulkhead in the engine compartment behind the engine control module. The relay module contains the following relays:
- ; Main relay - energised when the ignition is switched on and supplies power to the ECM.
- ; Fuel pump relay - energised by the ECM for a short period when the ignition is switched on, during cranking and while the engine is running.
- ; Starter relay - energised by the cranking signal from the ignition switch.
- ; Heated oxygen sensor relay - energised by the ECM and supplies current to the heated oxygen sensor element.
Fuel pump
The electric fuel pump is located inside the fuel tank and is energised by the ECM via the fuel pump relay in the relay module and the fuel cut-off switch. The fuel pump delivers more fuel than the maximum load requirement for the engine, pressure is therefore maintained in the fuel system under all conditions.

Fuel pressure regulator
The pressure regulator is a mechanical device mounted on one end of the fuel rail. Pressure is controlled by diaphragm spring pressure and modified by the vacuum signal. The regulator ensures that fuel rail pressure is maintained at a constant pressure difference to that in the inlet manifold, as manifold depression increases the regulated fuel pressure is reduced in direct proportion. When pressure exceeds the regulator setting, excess fuel is returned to the fuel tank swirl pot which contains the fuel pump pick-up.
Inertia fuel shut-off switch
The electrical circuit for the fuel pump incorporates an inertia switch which, in the event of a sudden deceleration, breaks the circuit to the fuel pump preventing fuel being delivered to the engine. The switch is situated next to the ECM and can be reset by pressing the rubber top.
WARNING: ALWAYS check for fuel leaks and the integrity of fuel system connections before resetting the switch.

Diagnostic connector
A diagnostic connector, located on the passenger compartment fusebox, allows engine tuning or fault diagnosis to be carried out using TestBook without disconnecting the ECM harness multiplug.

Heated oxygen sensor
The engine management system operates a closed loop emission system to ensure the most efficient level of exhaust gas conversion. A heated oxygen sensor, fitted in the exhaust down pipe, monitors the oxygen content of exhaust gases. The sensor generates a voltage related to the oxygen content of the exhaust. As the air/fuel mixture weakens, the exhaust oxygen content increases and so the voltage to the ECM decreases. If the mixture becomes richer, so the oxygen content decreases and the voltage increases. From this signal the ECM can determine if the air/fuel mixture being delivered to the engine is rich or lean. The ECM can adjust the duration that the injectors are open to maintain the air/fuel ratio necessary for efficient gas conversion by the catalyst. The heated oxygen sensor has an integral heating element to ensure an efficient operating temperature is quickly reached from cold. The electrical supply to the heater element is controlled by the ECM via the heated oxygen sensor relay in the relay module.

Acceleration enrichment
When the throttle pedal is depressed, the ECM receives a rising voltage from the throttle position sensor and detects a rise in manifold pressure from the manifold absolute pressure sensor. The ECM provides additional fuel by increasing the normal injector pulse width and also provides a number of extra additional pulses on rapid throttle openings. Over-run fuel cut-off The ECM implements over-run fuel cut-off when the engine speed is above 1600 rpm with engine at normal operating temperature and the throttle position sensor in the closed position, i.e. when ECM senses that the vehicle is ’coasting’ with the throttle pedal released. The ECM indexes the idle air control valve open slightly to increase the air flow through the engine to maintain a constant manifold depression to keep emissions low. Fuel is immediately reinstated if the throttle is opened. If engine speed drops below 1600 rpm on over-run, fuel is progressively reinstated. Over-speed fuel cut-off To prevent damage at high engine speeds the ECM will implement fuel cut-off at engine speeds above approximately 7000 rpm. Fuel is reinstated as engine speed falls.
Ignition switch off
In the first 10 seconds after ignition is switched off, the ECM drives the idle air control valve to its power down position (ready for the next engine start), and stores any required information. The ECM then monitors the engine bay temperature using the ambient air temperature sensor. If the temperature is above a certain limit, the ECM will drive the engine bay fan for 8 minutes, and will then power down. If the engine bay temperature is below the limit the ECM will power down after 10 seconds.
Engine compartment ambient air temperature sensor
The ECM monitors the engine compartment temperature using the ambient air temperature sensor. When the temperature exceeds a certain limit, the engine bay fan relay is energised to run the fan. If the temperature continues to rise, and exceeds another higher limit, the engine bay warning lamp (in the instrument pack) is illuminated. If the ambient air temperature sensor fails, the engine bay fan will run while the ignition is on and the warning lamp will be permanently lit.

1. Air cleaner element
2. Throttle disc
3. Idle air control valve
4. Inlet manifold
5. Injector
6. Evaporative emission cannister, purge valve
7. Evaporative emission cannister
Intake air is drawn into the throttle housing through an air filter element. Incorporated in the throttle housing are the throttle disc and the throttle position sensor. Air passes from the throttle housing via the manifold chamber into the inlet tracts. Fuel is sprayed into the inlet manifold by the injectors and the air/fuel mixture is drawn into the combustion chamber. Inlet manifold depression is measured by the MAP sensor which is mounted on the end of the manifold chamber. A signal from the MAP sensor is used by the ECM to calculate the amount of fuel to be delivered by the injectors.

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