Part 2
Electronic Engine Controls - 3.2L
Heated Oxygen (HO2S) Sensors
Four HO2S are used by the ECM to measure the oxygen content of the exhaust gasses leaving the engine. Two upstream sensors measure the gasses before they pass through the catalytic converter and two additional downstream sensors measure the gasses after they have passed through the catalytic converter.
The HO2S receive a fused power supply from the main relay in the BJB. Each HO2S is also connected to the ECM on three wires which provide a PWM control of the sensor heating coil, a ground and a signal line.
HO2S Preheating
The HO2S (often referred to as a Lambda (�) sensor) only operates efficiently at temperatures above 300 degrees C (572 degrees F). The normal operating temperature is between 300 degrees C and 850 degrees C (572 degrees F and 1562 degrees F) and the HO2S is electrically preheated so it reaches the optimum working temperature quickly. Another reason for the preheating is to maintain a normal operating temperature to prevent condensation which could damage the sensor.
The sensor heating coil is a PTC resistor. The heating coil is supplied with battery voltage via the main relay and provided with a ground by the ECM. When the ECM provides the ground the current will pass through the coil. When the sensor is cold, the resistance through the PTC resistor is low and a high current will pass through the coil. The ECM provides a PWM ground initially. As the PTC resistor heats up the resistance increases reducing the current flow. This is sensed by the ECM which gradually reduces the PWM ground to a continuous ground.
The coil is heated immediately following an engine start for a period of approximately 20 seconds and also during low load conditions when the temperature of the exhaust gasses is insufficient to maintain the optimum sensor temperature. The ECM controls the application of the PWM signal to prevent sensor damage due to thermal shock caused by the sensor heating too quickly. The ECM can diagnose faults in the heater coil and record fault codes which can be retrieved using a Land Rover approved diagnostic system.
Upstream HO2S
Two upstream HO2S are used and are located in each exhaust manifold, between the engine and the catalytic converter. The HO2S comprises a solid electrolyte Zirconium dioxide cell surrounded by a gas permeable ceramic. The output voltage from the sensor is dependent on the level of O passing through the permeable ceramic coating. Nominal voltage for �=1 is 300 to 500m V. As the fuel/air mixture becomes richer (�<1) the voltage rises to up to 900mV. As the mixture becomes weaker (�>1) the voltage falls towards 0mV.
The upstream HO2S is used by the ECM to monitor the oxygen content of the exhaust gasses leaving the engine before they reach the catalytic converter. The ECM will check the output from the HO2S to determine the combustion mixture and ensure �=1 is obtained. �=1 is the optimum air/fuel ratio which relates to a mixture of 14.7 kg air per 1 kg of fuel (14.7:1).
The HO2S uses current regulation and outputs a linear signal dependent on the ratio of exhaust gas oxygen to ambient oxygen. The oxygen content of the exhaust gasses is measured by comparing it with ambient air drawn into the HO2S.
Downstream HO2S
Two downstream HO2S are used and are located in the each exhaust system after the starter catalytic converter. The downstream HO2S are used by the ECM to monitor the oxygen content of the exhaust gasses leaving the catalytic converter. The ECM can use this information to check (when the conditions for catalyst diagnostics have been met) for correct operation of the catalytic converter.
The ECM uses the information from the downstream HO2S to enhance the signals from the upstream HO2S.
The downstream HO2S are similar in their construction to the upstream HO2S with the exception of the output signal to the ECM. The output signal is a binary signal where the amplitude of the signal curve changes considerably when the oxygen content in the exhaust gasses changes. The oxygen content of the exhaust gasses leaving the catalytic converter are measured by comparing it with ambient air drawn into the HO2S.
Stop Lamp Switch
The stop lamp switch is attached to the brake pedal bracket, adjacent to the speed control inhibit switch. When the brake pedal is pressed, a plate on the pedal moves away from the switch plunger allowing the plunger to extend and complete the switch contacts.
The switch receives a permanent, fused battery voltage via the BJB and the CJB. The switch is connected to the ECM which provides the ground path. The ground (battery voltage signal) is used by the ECM as a switch operation signal. The ground from the switch is routed via the CJB to the ECM which allows the CJB to also determine the switch operation.
The CJB uses the completed ground when the switch is operated to activate the stop lamps.
The ECM can diagnose the operation of the stop lamp switch and the status of the switch can be read using a Land Rover approved diagnostic system.
Ambient Air Temperature (AAT) Sensor
The AAT sensor is located in the underside of the Left Hand (LH) exterior door mirror. The sensor is a Negative Temperature Co-efficient (NTC) thermistor element. The element resistance decreases as the sensor temperature increases which produces a low signal voltage. The ECM supplies the sensor with a 5 V reference voltage and a ground and measures the returned signal voltage as an outside temperature.
The AAT signal is used by the ECM for a number of functions including engine cooling fan control and A/C compressor displacement control. The ECM also transmits a message on the high speed CAN bus relating to the current outside temperature for use by other control modules.
The ECM can diagnose the operation of the AAT sensor and the sensor output values can be read using a Land Rover approved diagnostic system.
Fuel Pump Driver Module (FPDM)
The FPDM is located in the LH rear corner of the luggage compartment, behind the trim panel and is secured to the LH chassis longitudinal with 2 screws.
The FPDM receives a battery supply via the fuel pump relay in the CJB. The relay is energized by the CJB when a request is received from the ECM. Two wires connect the FPDM to the fuel pump motor and a ground is via a body ground point. The ECM is connected to the FPDM on a single wire and this is used to control the pump pressure output and consequently the pump output pressure. The ECM uses signals from the MAP sensor, the fuel rail pressure/temperature sensor and the MAF/IAT sensor to determine and control the pump output.
The ECM outputs a PWM signal to the FPDM. The frequency of the signal determines the duty cycle of the FPDM which subsequently controls the pump pressure output. The frequency of the PWM signal represents half of the 'on' time of the pump. If the ECM outputs a PWM signal of 50% on time, the FPDM will operate the pump at 100% (permanently on). If the ECM outputs a PWM signal of 5%, the FPDM will operate the pump at 10% on time. The FPDM will only operate the fuel pump if it receives a PWM signal from the ECM of between 4% and 50%. If the ECM requires the pump to be stopped, the ECM transmits a PWM signal at a cycle of 75%.
If the power supply to the FPDM from the CJB or the fuel pump relay is disrupted for any reason, the fuel pump will not operate. The FPDM is monitored by the ECM for faults. Faults with the FPDM are stored in the ECM as fault codes which can be retrieved using a Land Rover approved diagnostic system.
Variable Camshaft Timing (VCT) Solenoid
The VCT solenoid is located in the LH end of the cylinder head and is secured with a bolt. The VCT solenoid is a valve which controls the oil flow to the VCT unit.
The VCT solenoid receives a fused battery supply via the main relay. The ECM provides a pulsed ground for the solenoid.
The VCT solenoid comprises an electro-magnetic valve with a spring loaded piston. Slots in the piston allows oil to be channelled to the VCT unit. The VCT unit rotates the inlet camshaft to adjust the camshaft timing as required. The direction in which the camshaft is rotated is dependent on the chamber in the VCT unit which is supplied with oil pressure from the slot in the VCT solenoid piston.
An oil filter is located in the intake channel for the VCT solenoid to prevent contaminants affecting the function of the valve.
Operation of the valve is controlled by the ECM. The ECM provides a PWM ground for the VCT solenoid. This allows oil to be directed to different chambers in the VCT unit at variable rates, allowing the camshaft angle position to be controlled smoothly and precisely.
The ECM can diagnose the operation of the VCT solenoid and store fault related codes. The codes can be read using a Land Rover approved diagnostic system.
Camshaft Profile Switching (CPS) Solenoid - Front/Rear
Two CPS solenoids are located at each end of the cylinder head, adjacent to the inlet camshaft and are each secured with a bolt. The CPS solenoids supply oil pressure to the hydraulic tappet locking pins allowing the camshaft profile to be changed. Each solenoid controls the oil pressure supply to the hydraulic tappet locking pins on 3 cylinders.
The CPS solenoids receive a fused battery supply via the main relay. The ECM provides a ground for the solenoid, which actuates a valve within the solenoid allowing oil pressure to adjust the camshaft profile.
The ECM can diagnose the operation of the CPS solenoids and store fault related codes. The codes can be read using a Land Rover approved diagnostic system.
Ignition Coils
Six plug top coils are used on the i6 engine and are located in recesses in the top of the cylinder head. The coils are controlled by the ECM and receive a fused, battery voltage supply via the main relay. The ECM controls the spark timing and production by switching the primary circuit of each coil to ground allowing the charge which has built up in the coil to produce a spark at the spark plug.
Each coil contains a power stage which controls the primary current and the ECM sends a signal to each coil to operate the power stage switching at the appropriate time. Each coil has a feedback wire to the ECM which allows the ECM to diagnose each individual coil and store fault related codes. The codes can be read using a Land Rover approved diagnostic system.
A suppressor is mounted on the camshaft cover adjacent to ignition coil 3 to prevent interference from the coils and/or the injectors affecting audio operation.
Fuel Injectors
Six fuel injectors are used on the i6 engine and are located on the inlet side of the cylinder head. The injectors are sealed in the cylinder head with O-ring seals and held in position by the fuel rail.
The injectors receive a fused battery voltage supply via the main relay. The ECM operates the injectors by grounding solenoid valves in the injector. When the ground is applied the solenoid valve operates and the injector sprays pressurized fuel from the fuel rail into the cylinder intake ports. The amount of fuel injected and the timing of the injection period is controlled by the ECM using data from other sensors.
The ECM can monitor the injector operation by monitoring the ground line from the injector. Each injector can be diagnosed by the ECM and fault codes stored. The codes can be read using a Land Rover approved diagnostic system.
Variable Intake System (VIS)
The VIS changes the length of the inlet manifold using two ECM controlled actuators which move flaps to control the air flow. The actuators operate singularly or together to adjust the length of the inlet tract.
Using an 'H' bridge, the intake and plenum actuator's internal electronics changes the actuator motor's polarity and therefore the flap position. At each flap position change, the DC actuator motor is powered for approximately 0.5 seconds. The worm gear design ensures that the flap remains in the desired position, even when the electric motors are not powered.
Intake Tract Variable Manifold
The ECM controls the position of the flaps by modulating the relevant actuator's control signal. If the signal shifts from low (approximately 1 volt) to high (approximately 10 volts) the internal electronics interpret it as the flap must close. If the signal shifts from high to low, the flap must open.
At engine speeds of less than 3800 rpm both the intake and plenum flaps are closed. At engine speeds of approximately 3800 rpm and higher the intake flap begins to open, effectively shortening the length of the intake manifold. At engine speeds of 4800 rpm or higher both the intake and plenum flaps are open, providing the shortest length of intake manifold.