Engine Controls - Self-Diagnostics - Without Codes: Overview Land Rover Discovery II

VEHICLE IDENTIFICATION

VEHICLE IDENTIFICATION

DESCRIPTION

Mode $06 enables access to the most current diagnostic results and thresholds of non-continuous diagnostic routines. Each individual parameter is identified by a Component Identifier (CID).

Following a power fail or after a delete error memory (Mode 3) request all values will be set to $00.

Values are stored in the battery backed RAM. Additional diagnostic results are available for LEV phase I, Phase II and ULEV vehicles.

PARAMETER DESCRIPTIONS

For J1979 Mode $06 Data parameter descriptions (Scheme 36), (Scheme 37) and see scheme 9.

Scheme 35

Scheme 36

Scheme 37

Catalyst monitoring is based on the monitoring of oxygen storage capability. The engine closed loop feedback control generates Lambda (air fuel ratio) oscillations in the exhaust gas. These oscillations are damped by the oxygen storage activity of the catalyst. The amplitude of the remaining Lambda oscillations downstream of the catalyst indicates the storage capability.

In order to determine catalyst efficiency, the amplitude ratio of the signal oscillations of the upstream and downstream Lambda sensors is determined. This information is evaluated separately in different engine load and speed ranges. If there is an indication of low storage capability in a certain number of operating ranges, a defective catalyst is diagnosed.

Note. Definition of Lambda: The stoichiometric air fuel ratio is the mass ratio of 14.7 kg of air to 1 kg of gasoline theoretically necessary for complete combustion. The excess air ratio (Lambda) indicates the deviation of the actual air fuel ratio from the theoretical air fuel ratio. Thus Lambda = actual inducted air mass/theoretical air requirement.

The method of engine misfire detection is based on evaluating engine speed fluctuations.

In order to detect misfiring in any cylinder, the torque of each cylinder is evaluated by recording the time between two ignition events; this is a measure of the mean value of the speed for this angular segment. Since a change in the engine torque results in a change of the engine speed. Additionally, the influence of the load torque at the wheels needs to be determined. This is to take account of the influences of different road surfaces, e.g. pavement, pot holes etc.

If the mean engine speed is measured, influences caused by road surfaces have to be eliminated.

This method consists of the following main parts

1. Data acquisition, including adaptation of the sensor wheel.
2. Calculation of engine roughness.
3. Comparison with a threshold, which depends on the operating conditions.
4. Identification of extreme conditions, during which misfire detection cannot be enabled due to a risk of falsely detecting misfire.
5. Fault processing, counting procedure of single misfire events, recording of any diagnostic trouble codes and MIL illumination.

For misfire monitoring structure, see

see scheme 14

Scheme 38

The secondary air injection system consists of an electric pump that is controlled by the ECM via a relay. Air is supplied by the pump to two vacuum operated control valves, one per cylinder bank. From each of the control valves air is delivered to the exhaust ports of the center two cylinders of each cylinder bank. The vacuum signal is switched via an ECM controlled solenoid valve. A vacuum reservoir ensures that there is always sufficient depression to operate the control valves.

Diagnosis of the secondary air injection system can take place in two steps. There is a passive diagnostic which checks for a lean shift in the signals from the front oxygen sensors during secondary air injection operation and there is an active check, which only runs if the passive check fails to achieve sufficient test results in any drive cycle. The active test has two parts; firstly the secondary air injection pump will be run with the control valves shut. If the valves are leaking or stuck open, the feedback fuelling will shift lean and a fault will be detected. If the valve check is passed, then the valves will be opened and if sufficient secondary airflow exists, then the fuelling will be shifted lean. If the lean shift is less than the required threshold, then a fault is stored.

Additionally, a total absence of secondary injection airflow does not cause the vehicle to exceed the appropriate monitoring threshold. Therefore the system only requires a functional check for the presence of secondary air.

The evaporative emission system monitoring permits the detection of leaks in the fuel evaporative emission control system with a diameter of 0.040" (1.0 mm) or larger. see scheme 22

For this purpose, a system pressure check is performed at idle with the vehicle stationary. Since vapor generation in the fuel tank could cause the false detection of a system leak, the first step is to close the EVAP canister purge valve and EVAP canister vent solenoid valve. Any pressure build-up is then measured, so that later results can be compensated for this fuel evaporation effect.

The EVAP canister purge valve is opened and the EVAP canister vent solenoid valve is closed. With this procedure a vacuum in the tank is created, which is measured by the fuel tank pressure sensor.

If no vacuum is detected, a large leak is assumed and the diagnosis is halted. If a large lean correction of the oxygen sensor controller is detected during the vacuum build-up, then the check is also halted, since fuel vapor is present in the system due to a high EVAP canister loading and idle instability will occur if the test is continued.

At a pre-determined vacuum the EVAP canister purge valve is closed, and the system is now considered CLOSED. From the gradient of the vacuum decay and the previously measured fuel vapor generation pressure rise, the presence of a leak can be inferred. The decay of the vacuum gradient also depends on the fuel level in the tank. The fuel level is roughly derived from the gradients of the vacuum build-up and vacuum decay and this information is also used when determining if a leak is present.

The evaporative emission monitoring system used for the Discovery 2001MY onwards permits the detection of leaks with a diameter of 0.020" (0.5 mm) or greater. This is achieved by means of a pressure test of the system. (Scheme 42), (Scheme 43) and (Scheme 44). This is performed by the DMTL, which is an electrically operated pump fitted to the atmospheric air intake of the EVAP Canister. From the 2002MY this unit contains an electric heater to prevent condensate formation.

The test proceeds in 2 stages

1. Reference Leak Measurement - The pump operates against the reference restriction within the DMTL. The ECM measures the current consumption of the pump motor during this phase.
2. Leak Measurement - The solenoid in the DMTL is operated in order to shut off normal purge airflow into the EVAP Canister. (Scheme 40) The pump can now pressurize the fuel tank and vapor handling system. The ECM again measures the current consumed by the pump motor and by comparing this with the reference current, determines if a leak is present or not. (Scheme 41) A high current indicates tight system and a low current indicates a leaking system.

For evaporative emission system monitoring with 0.020" (0.5 mm) diameter leak (Scheme 45), (Scheme 46) and see scheme 32.

Scheme 39

Scheme 40

Scheme 41

Scheme 42

Scheme 43

Scheme 44

Scheme 45

Scheme 46

Fuel Delivery System Abbreviations

Abbreviations for the fuel delivery system

1. QU1 - Upper Airflow Threshold Range 1
2. NU1 - Upper Engine Speed Threshold Range 1
3. tra - Additive Learning Correction Coefficient Per Time Unit (Range 1)
4. TRADN - Lower Diagnosis Threshold Of tra
5. TRADX - Upper Diagnosis Threshold Of tra
6. TLARN - Upper Engine Load Threshold f (n), Range 2
7. QL2 - Lower Airflow Threshold Range 2
8. TLL2 - Lower Engine Load Threshold Range 2
9. fra - Multiplicative Learning Correction Coefficient (Range 2)
10. FRADN - Lower Diagnosis Threshold Of fra
11. FRADX - Upper Diagnosis Threshold Of fra

The response rates of the upstream O2 sensors are monitored by measuring the period of the Lambda control oscillations. This period monitoring allows the detection of a slow O2 sensor. (Scheme 48)and see scheme 38.

Scheme 47

Scheme 48

Oxygen Sensor Heater Monitoring Description

For proper functioning of an oxygen sensor, its element must be heated. A non-functioning heater delays the oxygen sensor's readiness for closed loop control and influences emissions.

The monitoring function measures both oxygen sensor heater current (voltage drop over a shunt) and the heater voltage (heater supply voltage), so that the oxygen sensor heater resistance can be calculated. If the oxygen sensor heater resistance is exceeds a minimum or maximum threshold an oxygen sensor heater fault is detected.

The monitoring function is activated once per drive cycle, as long as the heater has been switched on for a certain time period and the current has stabilized.

Characteristics

1. ECM controlled switching of the oxygen sensor heater.
2. One shunt for each pair of oxygen sensors upstream and downstream of the catalysts for current measurement.

The diagnostic checks for a partially open thermostat, under conditions when the thermostat would be expected to be shut. (Scheme 50)

A second ECT sensor is installed in the outlet from the radiator. If the enablement criteria are met and the ECT is less than the normal thermostat opening temperature the diagnostic will run. (Scheme 51)

The diagnostic compares the difference between ECT and the radiator outlet temperature. This gives the temperature drop across the radiator. (Scheme 52)and (Scheme 53).

If the temperature drop is less than a threshold, and there is flow across the radiator, this is caused by leakage through the thermostat.

Scheme 49

Scheme 50

Scheme 51

Scheme 52

This sensor is the most important sensor on the vehicle, without it the engine cannot run. There is no backup strategy or limp home facility should it fail. The sensor produces the signal which enables the ECM to determine the angle of the crankshaft, and the engine RPM. From this, the point of ignition, fuel injection, etc. is calculated. If the signal wires are reversed, a 3° advance in timing will occur, as the electronics within the ECM uses the falling edge of the signal waveform as its reference/timing point for each tooth.

The reluctor is machined and has a tooth pattern based on 60 teeth at 6 degrees intervals and 3 degrees wide: two of the teeth are removed to provide a hardware reference mark which is 60 degrees before top dead center No. 1 cylinder. (Scheme 54)

Scheme 53

The sensor operates by generating an output voltage caused by the change in magnetic field, which occurs as the teeth pass in front of the sensor. The output voltage varies with the speed of the teeth passing the sensor; the higher the engine speed, the higher the output voltage. Note that the output is also dependent on the air gap between the sensor and the teeth (the larger the gap, the weaker the signal, the lower the output voltage).

There are two diagnostic checks on the output signal of this sensor

1. The hardware reference mark created by the missing teeth is outside the search window and the engine speed is greater than 500 RPM.
2. The hardware reference mark is outside the search window by more than one tooth and the engine speed is greater than 500 RPM.

The ECM transmits the engine speed to the automatic TCM using CAN, while all other control modules are hardwired. (Scheme 55)

Scheme 54

This is a Hall effect sensor producing four pulses for every two engine revolutions. The sensing element is positioned between 0.0-2.0 mm (0.0-0.079") from the side of the cam gear wheel. The sensor is, in effect, a magnetically operated electrical switch, switching a battery supply level voltage on or off dependent on the position of the cam gear wheel with respect to the sensor. (Scheme 56)

Scheme 55

The cam gear wheel has four slots machined in it enabling cylinder identification every 90°. The signal is used for cylinder recognition; enabling sequential fuel injection, knock control and cylinder identification for diagnostic purposes.

The system checks the camshaft position sensor signal at every software reference mark i.e., 54° before top dead center (2 teeth after the reluctor 2nd missing tooth). A fault condition is recognized if the signal does not change state (high to low or low to high voltage) every crankshaft revolution. (Scheme 57)

Scheme 56

This sensor is a temperature dependent resistor (thermistor), which is a Negative Temperature Co-efficient (NTC) type, i.e. resistance decreases with increasing temperature. The sensor forms part of a voltage divider chain with a pull up resistor within the ECM. The change in resistance relates to change in the ECT.

The sensor is vital to the correct running of the engine as a richer mixture is required at lower block temperatures for good quality starts and smooth running, leaning off as the temperature rises to maintain emissions and performance. Should the sensor fail there is a software ECT warm-up model which will supply a changing default value during the warm up stage of the engine, based upon IAT. After the software model reaches 60°C (140°F) ECT, a fixed default value of 85°C (185°F) is used. The model also forms part of the diagnostics for the ECT sensor, in conjunction with open and short circuit tests. (Scheme 58)

A fault condition is recognized if the ECM is powered up and the ECT sensor resistance exceeds a minimum or maximum threshold, or the difference between the ECT model and the temperature indicated by the ECT sensor is greater than a threshold.

Scheme 57

Airflow is determined by the cooling effect of the intake air passing over a "hot film" element contained within the device. The higher the air flow the greater the cooling effect and the lower the electrical resistance of the "hot film" element. The signal from the device is then used by the ECM to calculate the Mass Airflow (MAF) into the engine.

The measured airflow is used in determining the fuel quantity to be injected in order to maintain the stoichiometric air fuel ratio required for correct operation of the engine and exhaust catalysts. Should the device fail there is a software backup strategy that will be evoked once a fault has been diagnosed. A fault is detected if the MAF signal exceeds the maximum or minimum threshold for a given speed range or the difference between the calculated load and the actual MAF signal is too great. (Scheme 59)

Scheme 58

The Intake Air Temperature (IAT) sensor is a temperature dependent resistor (thermistor), i.e. the resistance of the sensor varies with temperature. The thermistor is an NTC type element, which means that the sensor resistance decreases as the sensor temperature increases. The sensor forms part of a voltage divider chain with an additional resistor in the ECM. The voltage from this network changes as the sensor resistance changes, relating the IAT to the voltage measured by the ECM.

A fault is detected if the resistance of the sensor exceeds a minimum or maximum threshold. (Scheme 60)

Scheme 59

The ECM uses active knock control, which serves to prevent engine damaging pre-ignition or detonation under all operating conditions enabling the engine to operate without additional safety margins. For the ECM to be able to determine the point at which a cylinder is pre-detonating, 2 piezo ceramic sensors are mounted on the engine block. Each sensor monitors all 4 cylinders in a bank (i.e. cylinders 1, 3, 5 & 7, and cylinders 2, 4, 6 and 8) by converting the engine block noise into a suitable electrical signal, which is then transmitted back to the ECM via a shielded cable. The signal is then processed within the ECM to identify the data that characterizes knocking. For knock sensor testing (Scheme 61)

There are three knock sensor diagnostic checks during which a fault is detected if

1. The sensor signal is less than the minimum engine RPM dependent threshold.
2. The sensor signal is greater than the maximum engine RPM dependent threshold.
3. The error counter for the verification of knock internal circuitry is exceeded.

Scheme 60

The sensor is a variable resistor, which is used to determine the position of the throttle plate and the rate of change in its angle. A software strategy within the ECM enables the closed throttle position to be learned, enabling the sensor to be fitted without the need for adjustment. The signal is used by the ECM as part of the transient fuelling strategy and to determine the closed throttle position for idle speed control, in conjunction with road speed.

The signal is not only checked for range (exceeds a minimum or maximum threshold), but also for plausibility against MAF. If the load-monitoring fault is stored, it is indicative of a blocked air filter or collapsed air intake duct etc. It is also probable that the altitude adaptation factor is incorrect under these conditions. For throttle position sensor testing (Scheme 62)

Scheme 61

The ECM performs a number of self-test integrity diagnostics on its internal hardware and software to check for faults. An error is detected if the ECM receives no CAN messages for at least 0.8 seconds, the calculated checksums at power down do not match the values stored in flash Electrically Erasable Programmable Read Only Memory (EEPROM) or the internal or external RAM fails a read/write test. For engine control module self test testing (Scheme 63)

Scheme 62

This input is required as part of the misfire detection system in order to record if a LOW FUEL situation was present when misfire was detected and logged as a fault. On Range Rover 38A the ECM is required to read an analogue fuel level input and determine the LOW FUEL condition from this signal. Discovery Series II had an active high digital input until 2000MY, at which point this input also became an analogue signal. For fuel level sensor testing (Scheme 64)

There are three fuel level input diagnostic checks, during which a fault is detected if

1. The input signal is less than a minimum voltage threshold.
2. The input signal is greater than a maximum voltage threshold.
3. The percentage difference between the fuel consumption calculated by the ECM and the change in the fuel tank level is greater than a threshold.

Scheme 63

The vehicle speed signal is transmitted from either the Self Levelling, Anti-lock Braking System (SLABS) or the ABS control module. This signal is then passed by the ECM to the automatic TCM via the CAN bus. The ECM has input diagnostics for this signal; the SLABS/ABS signal is compared to the vehicle speed signal on CAN from the automatic TCM, derived from the main gearbox output shaft speed; if the difference is greater than a threshold then a fault is detected. (Scheme 65)

Scheme 64

The ECM requires a permanent battery level voltage supply and a switched battery level voltage supply. The switched voltage supply is controlled by the ECM via a relay based on the condition of the ignition switch input (key position 2). At "key off" the ECM will maintain the switched supply active until various internal self-checks have been completed. (Scheme 66)

There are three battery voltage plausibility checks during which a fault is detected if

1. The battery voltage supply is less than a minimum voltage threshold.
2. The battery voltage supply is greater than a maximum voltage threshold and a jump-start condition has not been detected.
3. The battery voltage supply is less than a voltage threshold 60 seconds after the engine has been started.

Scheme 65

The SLABS/ABS control module transmits a PWM signal indicating rough road for misfire detection disablement. The ECM has input diagnostics for this signal. (Scheme 67)

There are three plausibility checks of the PWM signal during which a fault is detected if

1. The PWM signal is greater than a threshold indicating an electrical short to battery positive.
2. The PWM signal is less than a threshold indicating an electrical short to ground.
3. The PWM signal is greater than 44.92% but less than 55.08% indicating an error with the SLABS/ABS control module.

Scheme 66

This input indicates to the ECM that there is an OBD relevant error within the transfer box control module. The ECM will illuminate the MIL and store the P1701 DTC whenever this signal is true. The ECM carries out an integrity check on this signal following an IGNITION ON condition as shown below. (Scheme 68) The ECM detects a fault if any of the following conditions are satisfied

1. The line voltage is high during the low test.
2. The line voltage is low during the high test.
3. The line voltage is in an undefined state, neither high nor low.

For transfer box MIL request DTC testing, see

(Scheme 69)

Scheme 67

Scheme 68

The air conditioning system comprises of the Heating and Ventilation Control (Air Conditioning) Module (HeVAC), the air conditioning compressor and the condenser fans. The ECM controls the compressor clutch via a relay.

The control strategy of the relay features hysteresis to avoid the compressor clutch cycling while the engine is running. When there is a need for the compressor to be activated, the HeVAC module sends a request signal to the ECM, which in turn activates the compressor clutch relay. The condenser fan relay is controlled separately by both the ECM and the HeVAC module, and again, the control strategy features hysteresis to avoid the cooling fans cycling while the engine is running and the engine coolant and/or condenser temperatures fluctuate around a given threshold. When there is a need for condenser cooling for air conditioning performance the HeVAC module sends a request signal to the condenser fan relay. If there is a requirement for condenser cooling due to ECT, the ECM will send the request signal to the condenser fan relay.

When the HeVAC module requests air conditioning, the signal it sends to the ECM is through two binary switches, which sense the minimum and maximum refrigerant pressure and an evaporator thermostat. If the pressure or the temperature is below or above certain levels the binary switches will be open circuit and effectively disable the A/C request line to the ECM, which in turn will disengage the compressor clutch.

The air conditioning system is in standby mode if the HeVAC module is on and economy mode is not selected.

There are four diagnostic checks of the air conditioning system during which a fault is detected if

1. The A/C compressor clutch relay short circuit to battery positive, i.e. the driver voltage is greater than half the battery voltage when the driver is on.
2. The A/C compressor clutch relay short circuit to ground, i.e. the driver voltage is less than one third of the battery voltage when the driver is off.
3. The A/C compressor clutch relay is open circuit, i.e. the driver voltage is greater than one third of the battery voltage but less than two thirds of the battery voltage when the driver is off.
4. A/C has been requested when the system is not in standby mode, i.e. a signal rationality check.

For air conditioning system testing, see

(Scheme 70)

Scheme 69

The engine is fitted with 8 fuel injectors (one per cylinder), each of which is directly driven by the ECM. The Injectors are fed from a common fuel rail as part of a return less fuel system, with the fuel rail pressure constant at 3.5 bar (52 psi). The Fuel Pressure Regulator is integral to the fuel pump module, within the fuel tank. There is no reference signal line to the intake manifold.

The ECM monitors the output power stages of the injector drivers for electrical faults. A fault is detected if any of the following conditions is satisfied

1. Fuel injector driver short circuit to battery positive, i.e. the driver voltage is greater than half the battery voltage when the driver is on.
2. Fuel injector driver short circuit to ground, i.e. the driver voltage is less than one third of the battery voltage when the driver is off.
3. Fuel injector driver open circuit, i.e. the driver voltage is greater than one third of the battery voltage but less than two thirds of the battery voltage when the driver is off.

For fuel injectors testing, see

(Scheme 71)

Scheme 70

The load on an idling engine is a combination of both internal and external engine loads such as engine friction, water pump, air conditioning etc., which all change with time and operating conditions. The idle speed control actuator is required to enable closed loop idle speed control to compensate for these changing conditions, by regulating the airflow into the engine.

The device consists of two coils which use opposing PWM signals to control the position of opening/closing of the rotary valve. If one circuit fails the other is switched off by the ECM as soon as it recognizes the fault. This prevents the valve going to a maximum or minimum setting. There is a default position, which is determined by a permanent magnet. In the default condition the idle speed is raised and remains fixed at approximately 1200 RPM with no load.

There are eight idle speed control actuator diagnostic checks

1. Opening winding driver short circuit to battery positive, i.e. the driver voltage is greater than half the battery voltage when the driver is on.
2. Opening winding driver short circuit to ground, i.e. the driver voltage is less than one third of the battery voltage when the driver is off.
3. Opening winding driver open circuit, i.e. the driver voltage is greater than one third of the battery voltage but less than two thirds of the battery voltage when the driver is off.
4. Closing winding driver short circuit to battery positive, i.e. the driver voltage is greater than half the battery voltage when the driver is on.
5. Closing winding driver short circuit to ground, i.e. the driver voltage is less than one third of the battery voltage when the driver is off.
6. Closing winding driver open circuit, i.e. the driver voltage is greater than one third of the battery voltage but less than two thirds of the battery voltage when the driver is off.
7. Blocked Idle Air Control (IAC) valve - RPM error low, i.e. the engine speed is 100 RPM less than the target speed.
8. Blocked IAC valve - RPM error high, i.e. the engine speed is 180 RPM greater than the target speed.

For idle air control valve testing, see

(Scheme 72)

Scheme 71

The Land Rover V8 engine has a returnless fuel system. The fuel pressure regulator and filter are fitted to the IN TANK FUEL PUMP MODULE. The system pressure is maintained at a constant 3.5 bar (52 Psi), with no reference to intake manifold pressure. The ECM compensates for the non-constant pressure drop across the injector nozzles.

The fuel is supplied to the injectors from a fuel pump fitted within the fuel tank. The electrical supply to this fuel pump is controlled by the ECM via a relay and an Inertia fuel shutoff switch, which will turn off the fuel supply upon vehicle impact. The fuel system is pressurized to 3.5 bar (52 Psi) as soon as the ECM is powered up, the pump is then switched off until engine start has been achieved. If the pump runs but the fuel pressure is out of limits, adaptive fuel faults are stored. (Scheme 73)

The ECM monitors the output power stage of the fuel pump relay drive for electrical faults. A fault is detected if any of the following conditions is satisfied

1. Fuel pump relay driver short circuit to battery positive, i.e. the driver voltage is greater than half the battery voltage when the driver is on.
2. Fuel pump relay driver short circuit to ground, i.e. the driver voltage is less than one third of the battery voltage when the driver is off.
3. Fuel pump relay driver open circuit, i.e. the driver voltage is greater than one third of the battery voltage but less than two thirds of the battery voltage when the driver is off.

Scheme 72

The OBD system interfaces with the driver via the MIL, which is located in the instrument pack. A bulb check takes place every time the ignition is switched to ignition position II and until the engine is cranked.

The ECM monitors the driver junction temperature to detect an electrical fault. (Scheme 74) A fault is detected if the following condition is satisfied

1. MIL driver short circuit to battery positive, i.e. the driver stage junction temperature exceeds a temperature threshold.

Scheme 73

Hill Descent Control (HDC) operates in conjunction with the anti-lock braking system to provide greater control in off-road situations if necessary. HDC can be selected with the vehicle in any gear, but will only operate when low range gears are engaged with the vehicle traveling at less than 31 mph. During a descent, if engine braking is insufficient to control the vehicle speed, HDC (if selected) automatically operates the brakes to slow the vehicle and maintain a speed relative to the selected gear and the accelerator pedal position.

The ECM transmits throttle angle, engine torque, engine identification (V8 Thor) and transmission type to the SLABS control module to support the HDC system. This information is transmitted via a multiplexed PWM waveform.

The ECM has power stage diagnostics for the signal. (Scheme 75) A fault is detected if any of the following conditions is satisfied

1. HDC link to the SLABS control module short circuit to battery positive, i.e. the driver voltage is greater than half the battery voltage when the driver is on.
2. HDC link to the SLABS control module short circuit to ground, i.e. the driver voltage is less than one third of the battery voltage when the driver is off.
3. HDC link to the SLABS control module open circuit, i.e. the driver voltage is greater than one third of the battery voltage but less than two thirds of the battery voltage when the driver is off.

Scheme 74

The engine speed signal is sent by the ECM to the instrument pack, Body Control Module (BCM) and SLABS/ABS control module via a direct hardwired connection.

The ECM has power stage diagnostics for this signal. (Scheme 76) A fault is detected if any of the following conditions is satisfied

1. Engine speed signal driver short circuit to battery positive, i.e. the driver voltage is greater than half the battery voltage when the driver is on.
2. Engine speed signal driver short circuit to ground, i.e. the driver voltage is less than one third of the battery voltage when the driver is off.
3. Engine speed signal driver open circuit, i.e. the driver voltage is greater than one third of the battery voltage but less than two thirds of the battery voltage when the driver is off.

Scheme 75

This function is required to control the Environmental-Box (E-Box) mounted cooling fan. This fan provides cabin air into the E-Box to provide a cool temperature environment for the ECM fitted in the under-bonnet mounted E-Box. The temperature is determined by an internally (to the ECM) mounted temperature sensor. The fan will be switched on at 40°C +/- 15°C (104°F +/- 27°F) and also tested for 2 seconds every engine start.

The ECM has power stage diagnostics for this signal. (Scheme 77) A fault is detected if any of the following conditions is satisfied

1. E-Box cooling fan driver short circuit to battery positive, i.e. the driver voltage is greater than half the battery voltage when the driver is on.
2. E-Box cooling fan driver short circuit to ground, i.e. the driver voltage is less than one third of the battery voltage when the driver is off.
3. E-box cooling fan driver open circuit, i.e. the driver voltage is greater than one third of the battery voltage but less than two thirds of the battery voltage when the driver is off.

Scheme 76

The transmission range switch information and calculated range data are transmitted from the automatic TCM via the CAN bus.

The ECM performs a rationality test between these signals. (Scheme 78) A fault is detected if one the following conditions are satisfied

1. The transmission range switch information indicates low range and the calculated range information indicates high.
2. The transmission range switch information indicates high range and the calculated range information indicates low.

Scheme 77

The CAN is a high-speed serial interface for sharing dynamic signals between control modules. CAN communications are SELF CHECKED for errors, if an error is detected the message is ignored by the receiving control module. Due to the high rate of information exchange (500K baud) the system has a high degree of latency. This allows for a high amount of errors to be present without reducing the data transfer rate.

The CAN communication system is a differential bus using a twisted pair, which is normally very reliable. If either or both of the wires of the twisted pair CAN bus is open or short-circuited a CAN time out fault will occur and the automatic TCM defaults to third gear. In order to alert the driver the SPORT and MANUAL warning lights in the instrument pack will flash alternatively.

An error is detected if the ECM receives no CAN messages for at least 0.8 seconds or the duration of the automatic TCM retard request is greater than 10 seconds. (Scheme 79)

Scheme 78

A spiral oil separator is located in the stub pipe to the ventilation hose on the right hand cylinder head rocker cover, where oil is separated and returned to the cylinder head. The rubber ventilation hose from the right hand rocker cover is routed to a port on the right hand side of the inlet manifold plenum chamber where the returned gases mix with the fresh intake air passing through the throttle butterfly valve. see scheme 77 This pipe is primarily for part-load breathing and is connected to the engine via a restrictor that prevents an excessive vacuum building up in the crankcase at small throttle openings.

The stub pipe on the left hand rocker cover does not contain an oil separator or a restrictor and the ventilation hose is routed to the throttle body housing at the air inlet side of the butterfly valve. This pipe is for breathing at higher loads. Flow through this second pipe is negligible under normal driving conditions.

The ventilation hoses are attached to the stub pipes by metal band clamps.

Disconnection of the part-load breather is likely to result in a tendency of the engine to stall when returning to idle and the quantity of unmetered air, which flows into the intake manifold, will result in the detection of a fuel system fault by the OBD system.

For this reason, there are no separate monitors for compliance with the requirements of Positive Crankshaft Ventilation (PCV) monitoring.

Scheme 79