Part 2

Electronic Engine Controls

Accelerator Pedal Position Sensor (APP)





The APP (accelerator pedal position) sensor is located in a plastic housing which is integral with the throttle pedal. The housing is injection molded and provides location for the APP (accelerator pedal position) sensor. The sensor is mounted externally on the housing and is secured with two Torx screws. The external body of the sensor has a six pin connector which accepts a connector on the vehicle wiring harness.
The sensor has a spigot which protrudes into the housing and provides the pivot point for the pedal mechanism. The spigot has a slot which allows for a pin, which is attached to the sensor potentiometers, to rotate through approximately 90 degrees , which relates to pedal movement. The pedal is connected via a link to a drum, which engages with the sensor pin, changing the linear movement of the pedal into rotary movement of the drum. The drum has two steel cables attached to it. The cables are secured to two tension springs which are secured in the opposite end of the housing. The springs provide 'feel' on the pedal movement and require an effort from the driver similar to that of a cable controlled throttle. A detente mechanism is located at the forward end of the housing and is operated by a ball located on the drum. At near maximum throttle pedal movement, the ball contacts the detente mechanism. A spring in the mechanism is compressed and gives the driver the feeling
of depressing a 'kickdown' switch when full pedal travel is achieved.
The APP (accelerator pedal position) sensor signals are checked for range and plausibility. Two separate reference voltages are supplied to the pedal. Should one sensor fail, the other is used as a 'limp-home' input. In limp home mode due to an APP (accelerator pedal position) signal failure the ECM (engine control module) will limit the maximum engine speed to 2000 rpm.

APP Sensor Output Graph









The APP (accelerator pedal position) sensor has two potentiometer tracks which each receive a 5V input voltage from the ECM (engine control module). Track 1 provides an output of 0.5V with the pedal at rest and 2.0V at 100% full throttle. Track 2 provides an output of 0.5V with the pedal at rest and 4.5V at 100% full throttle. The signals from the two tracks are used by the ECM (engine control module) to determine fueling for engine operation and also by the ECM (engine control module) and the TCM (transmission control module) to initiate a kickdown request for the automatic transmission.
The ECM (engine control module) monitors the outputs from each of the potentiometer tracks and can determine the position, rate of change and direction of movement of the throttle pedal. The 'closed throttle' position signal is used by the ECM (engine control module) to initiate idle speed control and also overrun fuel cut-off.

Oxygen Sensors
There are four oxygen sensors located in the exhaust system. Two upstream before the catalytic converter (HO2S (heated oxygen sensor)) and two down stream after the catalytic converter (O2S (oxygen sensor)). The sensor monitors the level of oxygen in the exhaust gases and is used to control the fuel/air mixture. Positioning a sensor in the stream of exhaust gasses from each bank enables the ECM (engine control module) to control the fueling on each bank independently of the other, allowing much closer control of the air/fuel ratio and catalyst conversion efficiency.
The oxygen sensors need to operate at high temperatures in order to function correctly. To achieve the high temperatures required, the sensors are fitted with heater elements that are controlled by a PWM (pulse width modulation) signal from the ECM (engine control module). The heater elements are operated immediately following engine start and also during low load conditions when the temperature of the exhaust gases is insufficient to maintain the required sensor temperatures. A non-functioning heater delays the sensor's readiness for closed loop control and influences emissions. The PWM (pulse width modulation) duty cycle is carefully controlled to prevent thermal shock to cold sensors.
HO2S (heated oxygen sensor) sensors also known as Linear or "Wide Band" sensors produces a constant voltage, with a variable current that is proportional to the oxygen content. This allows closed loop fueling control to a target lambda, i.e. during engine warm up (after the sensor has reached operating temperature and is ready for operation). This improves emission control.
The O2S (oxygen sensor) sensor uses Zirconium technology that produces an output voltage dependant upon the ratio of exhaust gas oxygen to the ambient oxygen. The device contains a Galvanic cell surrounded by a gas permeable ceramic, the voltage of which depends upon the level of O2 (oxygen) defusing through. Nominal output voltage of the device for l =1 is 300 to 500m volts. As the fuel mixture becomes richer (l<1) the voltage tends towards 900m volts and as it becomes leaner (l>1) the voltage tends towards 0 volts. Maximum tip temperature is 1,000 Degrees Celsius for a maximum of 100 hours.
Sensors age with mileage, increasing their response time to switch from rich to lean and lean to rich. This increase in response time influences the ECM (engine control module) closed loop control and leads to progressively increased emissions. Measuring the period of rich to lean and lean to rich switching monitors the response rate of the upstream sensors.
Diagnosis of electrical faults is continually monitored in both the upstream and downstream sensors. This is achieved by checking the signal against maximum and minimum threshold, for open and short circuit conditions.
Oxygen sensors must be treated with the utmost care before and during the fitting process. The sensors have ceramic material within them that can easily crack if dropped/banged or over-torqued. The sensors must be torqued to the required figure, (40-50 Nm), with a calibrated torque wrench. Care should be taken not to contaminate the sensor tip when anti-seize compound is used on the thread. Heated sensor signal pins are tinned and universal are gold plated. Mixing up sensors could contaminate the connectors and affect system performance.

Failure Modes
- Mechanical fitting & integrity of the sensor.
- Sensor open circuit/disconnected.
- Short circuit to vehicle supply or ground.
- Lambda ratio outside operating band.
- Crossed sensors bank A & B.
- Contamination from leaded fuel or other sources.
- Change in sensor characteristic.
- Harness damage.
- Air leak into exhaust system.

Failure Symptoms
- Default to Open Loop fueling for the particular cylinder bank
- High CO (carbon monoxide) reading.
- Strong smell of HO2S (heated oxygen sensor) till default condition.
- Excess Emissions.
It is possible to fit front and rear sensors in their opposite location. However the harness connections are of different gender and color to ensure that the sensors cannot be incorrectly connected. In addition to this the upstream sensors have two holes in the shroud, whereas the down stream sensors have four holes in the shroud for the gas to pass through.

Generator





The Generator has a power control module voltage regulator for use in a 14V charging system with 6÷12 zener diode bridge rectifiers.
The ECM (engine control module) monitors the load on the electrical system via PWM (pulse width modulation) signal and adjusts the generator output to match the required load. The ECM (engine control module) also monitors the battery temperature to determine the generator regulator set point. This characteristic is necessary to protect the battery; at low temperatures battery charge acceptance is very poor so the voltage needs to be high to maximize any rechargeability, but at high temperatures the charge voltage must be restricted to prevent excessive gassing of the battery with consequent water loss.
The Generator has a smart charge capability that will reduce the electrical load on the Generator reducing torque requirements, this is implemented to utilize the engine torque for other purposes. This is achieved by monitoring three signals to the ECM (engine control module):
- Generator sense (A sense), measures the battery voltage at the CJB (central junction box).
- Generator communication (Alt Com) communicates desired Generator voltage set point from ECM (engine control module) to Generator.
- Generator monitor (Alt Mon) communicates the extent of Generator current draw to ECM (engine control module). This signal also transmits faults to the ECM (engine control module) which will then sends a message to the instrument pack on the CAN (controller area network) bus to illuminate the charge warning lamp.

Fuel Injectors





The engine has 6 fuel injectors (one per cylinder), each injector is directly driven by the ECM (engine control module). The injectors are fed by a common fuel rail as part of a 'returnless' fuel system. The fuel rail pressure is regulated to 4.5 bar by a fuel pressure regulator which is integral to the fuel pump module, within the fuel tank. The injectors can be checked by resistance checks. There is a fuel pressure test Schrader valve attached to the fuel rail on the front LH side for fuel pressure testing purposes. The ECM (engine control module) monitors the output power stages of the injector drivers for electrical faults.
The injectors have a resistance of 13.8 Ohms ± 0.7 Ohms @ 20 Degrees Celsius.

Ignition Coils





The engine is fitted with six plug-top coils that are driven directly by the ECM (engine control module). This means that the ECM (engine control module), at the point where sufficient charge has built up, switches the primary circuit of each coil and a spark is produced in the spark plug. The positive supply to the coil is fed from a common fuse. Each coil contains a power stage to trigger the primary current. The ECM (engine control module) sends a signal to each of the coils power stage to trigger the power stage switching. Each bank has a feedback signal that is connected to each power stage. If the coil power stage has a failure the feedback signal is not sent, causing the ECM (engine control module) to store a fault code appropriate to the failure.
The ECM (engine control module) calculates the dwell time depending on battery voltage and engine speed to ensure constant secondary energy. This ensures sufficient secondary (spark) energy is always available, without excessive primary current flow thus avoiding overheating or damage to the coils.
The individual cylinder spark timing is calculated from a variety of inputs:
- Engine speed and load.
- Engine temperature.
- Knock control.
- Auto gearbox shift control.
- Idle speed control.


Fuel Rail Pressure Sensor





The fuel rail pressure sensor is located on top of the fuel rail adjacent to the fuel inlet. The fuel rail pressure sensor measures the pressure of the fuel in the fuel rail. This input is then used by the fuel pump control module to control the amount of fuel delivered to the fuel rail.

Fuel Pump Driver Module





The FPDM (fuel pump driver module) is located on the RH side of the charcoal canister on top of the fuel tank. The fuel pump control module receives a power supply via the fuel pump relay in the auxiliary fuse box.
The ECM (engine control module) sends a PWM (pulse width modulation) signal to the FPDM (fuel pump driver module), the duty cycle of the signal determines the duty cycle of the pump. The ECM (engine control module) sets a target fuel pressure based on engine load. The target fuel pressure is maintained by using feedback from the fuel rail pressure sensor which is used to control the fuel pump via a closed loop PWM (pulse width modulation) signal. The PWM (pulse width modulation) signal to the pump represents half the ON time of the pump. If the ECM (engine control module) transmits a 50% on time the fuel pump control module drives the pump at 100%. If the ECM (engine control module) transmits a 5% ON time the fuel pump control module drives the pump at 10%. The fuel pump control module will only turn
the fuel pump ON if it receives a valid signal between 4% and 50%. When the ECM (engine control module) requires the fuel pump to be turned OFF the ECM (engine control module) transmits a duty cycle signal of 75%.
The status of the FPDM (fuel pump driver module) is monitored by the ECM (engine control module). Any errors can be retrieved from the ECM (engine control module). The fuel pump control module cannot be interrogated for diagnostic purposes.
The ECM (engine control module) controls the FPDM (fuel pump driver module) in response to inputs from the fuel rail pressure sensor, MAP (manifold absolute pressure) and the MAF (mass air flow)/IAT (intake air temperature) sensor.


Variable Valve Timing (VVT)
Variable valve timing is used on the V6 engine to enhance low and high speed engine performance and idle speed quality.
For each intake camshaft the VVT (variable valve timing) system comprises:
- VVT (variable valve timing) unit
- Valve timing solenoid
The VVT (variable valve timing) system alters the phase of the intake valves relative to the fixed timing of the exhaust valves, to alter:
- The mass of air flow to the cylinders.
- The engine torque response.
- Emissions.
The VVT (variable valve timing) unit uses a vane type device to control the camshaft angle. The system operates over a range of 48 degrees and is advanced or retarded to its optimum position within this range.
The VVT (variable valve timing) system is controlled by the ECM (engine control module) based on engine load and speed along with engine oil temperature to calculate the appropriate camshaft position.
The VVT (variable valve timing) system provides the following advantages:
- Reduced engine emissions and improved fuel consumption which in turn improves the engines internal EGR (exhaust gas recirculation) effect over a wider operating range.
- Enhanced full load torque characteristics.
- Improved fuel economy through optimized torque over the engine speed range.

Variable Valve Timing Unit









The VVT (variable valve timing) unit is a hydraulic actuator mounted on the end of the intake camshaft. The unit advances or retards the camshaft timing to alter the camshaft to crankshaft phase. The ECM (engine control module) controls the VVT (variable valve timing) timing unit via an oil control solenoid. The oil control solenoid routes oil pressure to the advance or retard chambers either side of the vanes within the VVT (variable valve timing) unit.
The VVT (variable valve timing) unit is driven by the primary drive chain and rotates relative to the exhaust camshaft. When the ECM (engine control module) requests a retard in camshaft timing the oil control solenoid is energized which moves the shuttle valve in the solenoid to the relevant position allowing oil pressure to flow out of the advance chambers in the VVT (variable valve timing) unit whilst simultaneously allowing oil pressure into the retard chambers.
The ECM (engine control module) controls the advancing and retarding of the VVT (variable valve timing) unit based on engine load and speed. The ECM (engine control module) sends an energize signal to the oil control solenoid until the desired VVT (variable valve timing) position is achieved. When the desired VVT (variable valve timing) position is reached, the energizing signal is reduced to hold the oil control solenoid position and consequently desired VVT (variable valve timing) position. This function is under closed loop control and the ECM (engine control module) can sense any variance in shuttle valve oil pressure via the camshaft position sensor and can adjust the energizing signal to maintain the shuttle valve hold position.
operation can be affected by engine oil temperature and properties. At very low oil temperatures the movement of the VVT (variable valve timing) mechanism will be slow due to the high viscosity of the oil. While at high oil temperatures the low oil viscosity may impair the VVT (variable valve timing) operation at low oil pressures. The oil pump has the capacity to cope with these variations in oil pressure while an oil temperature sensor is monitored by the ECM (engine control module) to provide oil temperature feedback. At extremely high oil temperatures the ECM (engine control module) may limit the amount of VVT (variable valve timing) advance in order to prevent the engine from stalling when returning to idle speed.
VVT (variable valve timing) does not operate when engine oil pressure is below 1.25 bar. This is because there is insufficient pressure to release the VVT (variable valve timing) units internal stopper pin. This occurs when the engine is shut down and the VVT (variable valve timing) unit has returned to the retarded position. The stopper pin locks the VVT (variable valve timing) unit to the camshaft to ensure camshaft stability during the next start up.

Valve Timing Solenoid





Valve Timing Solenoid
The valve timing solenoid controls the position of the shuttle valve in the bush carrier. A plunger on the solenoid extends when the solenoid is energized and retracts when the solenoid is de-energized.
When the valve timing solenoids are de-energized, the coil springs in the bush carriers position the shuttle valves to connect the valve timing units to drain. In the valve timing units, the return springs hold the ring pistons and gears in the retarded position. When the valve timing solenoids are energized by the ECM (engine control module), the solenoid plungers position the shuttle valves to direct engine oil to the valve timing units. In the valve timing units, the oil pressure overcomes the force of the return springs and moves the gears and ring pistons to the advanced position. System response times are 1.0 second maximum for advancing and 0.7 second maximum for retarding. While the valve timing is in the retarded mode, the ECM (engine control module) produces a periodic lubrication pulse. This momentarily energizes the valve timing solenoids to allow a spurt of oil into the valve timing units. The lubrication pulse
occurs once every 5 minutes.