Part 2

Electronic Engine Controls

HEATED OXYGEN SENSORS





The heated oxygen sensors allow the ECM (engine control module) to measure the oxygen content of the exhaust gases, for closed loop control of the air:fuel mixture and for catalytic converter monitoring.
An upstream heated oxygen sensor is installed in the outlet of each exhaust manifold, which enables independent control of the air:fuel mixture for each cylinder bank. A downstream heated oxygen sensor is installed in each catalytic converter, which enables the performance of the catalytic converters to be monitored.
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 after each engine start and during low load conditions when the temperature of the exhaust gases is insufficient to maintain the required sensor temperature. The PWM (pulse width modulation) duty cycle is carefully controlled to prevent thermal shock to cold sensors. A non-functioning heater delays the sensor's readiness for closed loop control and increases emissions.
The upstream heated oxygen sensors produce a constant voltage, with a variable current that is proportional to the lambda ratio. The downstream heated oxygen sensors produce an output voltage dependant on the ratio of the exhaust gas oxygen to the ambient oxygen.
The heated oxygen 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.
If a heated oxygen sensor fails:
- The ECM (engine control module) defaults to open loop fueling for the related cylinder bank
- The CO (carbon monoxide) and emissions content of the exhaust gases increases
- The exhaust smells of rotten eggs (hydrogen sulphide).
With a failed heated oxygen sensor, the engine will suffer from unstable operation and reduced performance.

ACCELERATOR PEDAL POSITION SENSOR









The APP (accelerator pedal position) sensor allows the ECM (engine control module) to determine the driver requests for vehicle speed, acceleration and deceleration. The ECM (engine control module) uses this information to determine the setting of the electronic throttle.
The APP (accelerator pedal position) sensor is located on the accelerator pedal and secured with two Torx screws. The sensor has a six pin connector which provides the interface with the vehicle harness.
The APP (accelerator pedal position) sensor has a spigot which protrudes into the housing of the accelerator pedal 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.

APP Sensor Output Graph









The APP (accelerator pedal position) sensor has two potentiometer tracks which each receive a 5 V input voltage from the ECM (engine control module). Track 1 provides an output of 0.5 V with the pedal at rest and 2.0 V at 100% full throttle. Track 2 provides an output of 0.5 V with the pedal at rest and 4.5 V 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 overrun fuel cut-off.
The APP (accelerator pedal position) sensor signals are checked for range and plausibility. Should one signal fail, the ECM (engine control module) adopts a limp home mode, which limits the engine speed to 2000 rev/min maximum.

AMBIENT AIR TEMPERATURE SENSOR





The AAT (ambient air temperature) sensor is a NTC (negative temperature coefficient) thermistor that allows the ECM (engine control module) to monitor the temperature of the air around the vehicle. The ECM (engine control module) uses the AAT input for a number of functions, including engine cooling fan control. The ECM (engine control module) also transmits the ambient temperature on the high speed CAN (controller area network) bus for use by other control modules.
The AAT sensor is installed in the LH (left-hand) exterior mirror, with the bulb of the sensor positioned over a hole in the bottom of the mirror casing.
The ECM (engine control module) supplies the sensor with a 5 V reference voltage and a ground, and translates the return signal voltage into a temperature.
If there is a fault with the AAT sensor, the ECM (engine control module) calculates the AAT from the temperature inputs of the MAFT (mass air flow and temperature) sensors. If the AAT sensor and the temperature inputs of the MAFT (mass air flow and temperature) sensors are all faulty, the ECM (engine control module) adopts a default ambient temperature of 20 °C (68 °F).

ELECTRONIC THROTTLE





The ECM (engine control module) uses the electronic throttle to regulate engine torque.
The electronic throttle is installed between the T piece duct, of the intake air distribution and filtering system, and the inlet of the SC (supercharger). For additional information, refer to Intake Air Distribution and Filtering Intake Air Distribution and Filtering
The throttle plate is operated by an electric DC (direct current) motor integrated into the throttle body. The ECM (engine control module) uses a PWM (pulse width modulation) signal to control the DC motor. The ECM (engine control module) compares the APP (accelerator pedal position) sensor inputs against an electronic map to determine the required position of the throttle plate. The ECM (engine control module) and electronic throttle are also required to:
- Monitor requests for cruise control operation
- Automatically operate the electronic throttle for accurate cruise control
- Perform all dynamic stability control engine interventions
- Monitor and carry out maximum engine speed and road speed cut outs
- Provide different engine maps for the ride and handling optimization system.
A software strategy within the ECM (engine control module) calibrates the position of the throttle plate at the beginning of each ignition cycle. When the ignition is turned on, the ECM (engine control module) performs a self test and calibration routine by fully closing the throttle plate and then opening it again. This tests the default position springs and allows the ECM (engine control module) to learn the position of the closed hard stop. Subsequently the ECM (engine control module) keeps the throttle plate a minimum of 0.5 degree from the closed hard stop.

ECM RELAY
The ECM (engine control module) relay is used to initiate the power up and power down routines within the ECM (engine control module). The main relay is installed in the EJB (engine junction box).
When the ignition is turned on, battery voltage is applied to the ignition sense input. The ECM (engine control module) then starts its power up routines and energizes the ECM (engine control module) relay.
When the ignition is turned off, the ECM (engine control module) maintains its powered up state while it conducts the power down routines (up to 20 minutes in extreme cases, when cooling fans are required) and on completion will turn off the ECM (engine control module) relay.

CONTROL DIAGRAM

Sheet 1 of 2

NOTE:
A = Hardwired.









Sheet 2 of 2

NOTE:
A = Hardwired; D = High speed CAN (controller area network) bus.









OPERATION

ECM Adaptations
The ECM (engine control module) has the ability to adapt the input values it uses to control certain outputs. This capability maintains engine refinement and ensures the engine emissions remain within the legislated limits. The components which have adaptations associated with them are:
- The APP (accelerator pedal position) sensor
- The heated oxygen sensors
- The MAFT (mass air flow and temperature) sensors
- The CKP (crankshaft position) sensor
- Electronic throttle.

Oxygen and MAFT Sensors
There are several adaptive maps associated with the fueling strategy. Within the fueling strategy the ECM (engine control module) calculates short-term adaptations and long term adaptations. The ECM (engine control module) will monitor the deterioration of the heated oxygen sensors over a period of time. It will also monitor the current correction associated with the sensors.
The ECM (engine control module) will store a fault code in circumstances where an adaption is forced to exceed its operating parameters. At the same time, the ECM (engine control module) will record the engine speed, engine load and intake air temperature.

Crankshaft Position Sensor
The characteristics of the signal supplied by the CKP (crankshaft position) sensor are learned by the ECM (engine control module). This enables the ECM (engine control module) to set an adaption and support the engine misfire detection function. Due to the small variation between different drive plates and different CKP (crankshaft position) sensors, the adaption must be reset if either component is renewed, or removed and refitted. It is also necessary to reset the drive plate adaption if the ECM (engine control module) is renewed or replaced. The ECM (engine control module) supports four drive plate adaptations for the CKP (crankshaft position) sensor. Each adaption relates to a specific engine speed range. The
engine speed ranges are detailed in the table below:





Misfire Detection
Legislation requires that the ECM (engine control module) must be able to detect the presence of an engine misfire. It must be able to detect misfires at two separate levels. The first level is a misfire that could lead to the legislated emissions limit being exceeded by a given amount. The second level is a misfire that may cause catalytic converter damage.
The ECM (engine control module) monitors the number of misfire occurrences within two engine speed ranges. If the ECM (engine control module) detects more than a predetermined number of misfire occurrences within either of these two ranges, over two consecutive journeys, it will record a fault code and details of the engine speed, engine load and engine coolant temperature. In addition, the ECM (engine control module) monitors the number of misfire occurrences that happen in a 'window' of 200 engine revolutions. The misfire occurrences are assigned a weighting according to their likely impact on the catalytic converters. If the number of misfires exceeds a given value, the ECM (engine control module) stores catalytic converter damage fault codes, along with the engine speed, engine load and engine coolant temperature.
The signal from the CKP (crankshaft position) sensor indicates how fast the poles on the drive plate are passing the sensor tip. A sine wave is generated each time a pole passes the sensor tip. The ECM (engine control module) can detect variations in drive plate speed by monitoring the sine wave signal supplied by the crankshaft position sensor. By assessing this signal, the ECM (engine control module) can detect the presence of an engine misfire. At this time, the ECM (engine control module) will assess the amount of variation in the signal received from the CKP (crankshaft position) sensor and assign a roughness value to it. This roughness value can be viewed within the real time monitoring feature using Land Rover approved diagnostic equipment. The ECM (engine control module) will evaluate the signal against a number of factors and will decide whether to record the occurrence or ignore it. The ECM (engine control module) can assign a roughness and misfire signal for each cylinder.

Diagnostics
The ECM (engine control module) stores each fault as a DTC (diagnostic trouble code). The DTC (diagnostic trouble code) and associated environmental and freeze frame data can be read using Land Rover approved diagnostic equipment, which can also read real time data from each sensor, the adaption values currently being employed and the current fueling, ignition and idle speed settings.