2002 LAND ROVER DISCOVERY sensor

EMISSION CONTROL - V8
DESCRIPTION AND OPERATION 17-2-37
In the case of a catalytic converter failure the following failure symptoms may be apparent:
lMIL light on after 2 driving cycles (NAS market only).
lHigh exhaust back pressure if catalyst partly melted.
lExcessive emissions
lStrong smell of H
2S (rotten eggs).
Oxygen sensor voltages can be monitored using 'Testbook', the approximate output voltage from the heated oxygen
sensors with a warm engine at idle and with closed loop fuelling active are shown in the table below:
Mass air flow sensor and air temperature sensor
The engine management ECM uses the mass air flow sensor to measure the mass of air entering the intake and
interprets the data to determine the precise fuel quantity which needs to be injected to maintain the stoichiometric
air:fuel ratio for the exhaust catalysts. If the mass air flow sensor fails, lambda control and idle speed control will be
affected and the emission levels will not be maintained at the optimum level. If the device should fail and the ECM
detects a fault, it invokes a software backup strategy.

+ ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine
management.
The air temperature sensor is used by the engine management ECM to monitor the temperature of the inlet air. If the
device fails, catalyst monitoring will be affected. The air temperature sensor in integral to the mass air flow sensor.

+ ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine
management.
Throttle position sensor
If the engine management ECM detects a throttle position sensor failure, it may indicate a blocked or restricted air
intake filter. Failure symptoms may include:
lPoor engine running and throttle response
lEmission control failure
lNo closed loop idle speed control
lAltitude adaption is incorrect
If a signal failure should occur, a default value is derived using data from the engine load and speed.

+ ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine
management.
Atmospheric pressure will vary with altitude and have a resulting influence on the calculations performed by the ECM
in determining the optimum engine operating conditions to minimise emissions. The following are approximate
atmospheric pressures for the corresponding altitudes:
l0.96 bar at sea level
l0.70 bar at 2,750 m (9,000 ft.)
Measurement Normal catalyst Defective catalyst
Pre-catalytic heated oxygen sensors ~ 100 to 900 mV switching @ ~ 0.5
Hz~ 100 to 900 mV switching @ ~ 0.5 Hz
Post-catalytic heated oxygen sensors ~ 200 to 650 mV, static or slowly
changing~ 200 to 850 mV, changing up to same
frequency as pre-catalytic heated oxygen
sensors
Amplitude ratio (LH HO
2 sensors & RH
HO
2 sensors)<0.3 seconds >0.6 seconds (needs to be approximately
0.75 seconds for single catalyst fault)
Number of speed/load monitoring areas
exceeded (LH & RH)0 >1 (needs to be 3 for fault storage)

EMISSION CONTROL - V8
DESCRIPTION AND OPERATION 17-2-39
Possible symptoms associated with a purge valve or associated pipework failure is listed below:
lEngine may stall on return to idle if purge valve is stuck open.
lPoor idling quality if the purge valve is stuck open
lFuelling adaptions forced excessively lean if the EVAP canister is clear and the purge valve is stuck open.
lFuelling adaptions forced excessively rich if the EVAP canister is saturated and the purge valve is stuck open.
lSaturation of the EVAP canister if the purge valve is stuck closed.
To maintain driveability and effective emission control, EVAP canister purging must be closely controlled by the
engine management ECM, as a 1% concentration of fuel vapour from the EVAP canister in the air intake may shift
the air:fuel ratio by as much as 20%. The ECM must purge the fuel vapour from the EVAP canister at regular intervals
as its storage capacity is limited and an excessive build up of evaporated fuel pressure in the system could increase
the likelihood of vapour leaks. Canister purging is cycled with the fuelling adaptation as both cannot be active at the
same time. The ECM alters the PWM signal to the purge valve to control the rate of purging of the canister to maintain
the correct stoichiometric air:fuel mixture for the engine.
Fuel leak detection system (vacuum type) – NAS only
The advanced evaporative loss control system used on NAS vehicles is similar to the standard system, but also
includes a CVS valve and fuel tank pressure sensor and is capable of detecting holes in the fuel evaporative system
down to 1 mm (0.04 in.). The test is carried out in three parts. First the purge valve and the canister vent solenoid
valve closes off the storage system and the vent pressure increases due to the fuel vapour pressure level in the tank.
If the pressure level is greater than the acceptable limit, the test will abort because a false leak test response will
result. In part two of the test, the purge valve is opened and the fuel tank pressure will decrease due to the depression
from the intake manifold, evident at the purge port of the EVAP canister during purge operation. In part three of the
test, the leak measurement test is performed. The pressure response of the tests determines the level of leak, and if
this is greater than the acceptable limit on two consecutive tests, the ECM stores the fault in diagnostic memory and
the MIL light on the instrument pack is illuminated. The test is only carried out at engine idle with the vehicle stationary,
and a delay of 15 minutes after engine start is imposed before diagnosis is allowed to commence.

EMISSION CONTROL - V8
17-2-40 DESCRIPTION AND OPERATION
EVAP system, leak detection diagnostic (vacuum type)
The EVAP system leak detection is performed as follows:
1The ECM checks that the signal from the fuel tank pressure sensor is within the expected range. If the signal is
not within range, the leakage test will be cancelled.
2Next the purge valve is held closed and the canister vent solenoid (CVS) valve is opened to atmosphere. If the
ECM detects a rise in pressure with the valves in this condition, it indicates there is a blockage in the fuel
evaporation line between the CVS valve and the EVAP canister, or that the CVS valve is stuck in the closed
position and thus preventing normalisation of pressure in the fuel evaporation system. In this instance, the
leakage test will be cancelled.
3The CVS valve and the purge valve are both held in the closed position while the ECM checks the fuel tank
pressure sensor. If the fuel tank pressure sensor detects a decline in pressure, it indicates that the purge valve
is not closing properly and vapour is leaking past the valve seat face under the influence of the intake manifold
depression. In this instance, the leakage test will be cancelled.
4If the preliminary checks are satisfactory, a compensation measurement is determined next. Variations in fuel
level occur within the fuel tank, which will influence the pressure signal detected by the fuel tank pressure
sensor. The pressure detected will also be influenced by the rate of change in the fuel tank pressure, caused by
the rate of fuel evaporation which itself is dependent on the ambient temperature conditions. Because of these
variations, it is necessary for the ECM to evaluate the conditions prevailing at a particular instance when testing,
to ensure that the corresponding compensation factor is included in its calculations.
The CVS valve and purge valves are both closed while the ECM checks the signal from the fuel tank pressure
sensor. The rise in fuel pressure detected over a defined period is used to determine the rate of fuel evaporation
and the consequent compensation factor necessary.
5With the CVS valve still closed, the purge valve is opened. The inlet manifold depression present while the purge
valve is open, decreases EVAP system pressure and sets up a small vacuum in the fuel tank. The fuel tank
pressure sensor is monitored by the ECM and if the vacuum gradient does not increase as expected, a large
system leak is assumed by the ECM (e.g. missing or leaking fuel filler cap) and the diagnostic test is terminated.
If the EVAP canister is heavily loaded with hydrocarbons, purging may cause the air:fuel mixture to become
excessively rich, resulting in the upstream oxygen sensors requesting a leaner mix from the ECM to bring the
mixture back to the stoichiometric ideal. This may cause instability in the engine idle speed and consequently
the diagnostic test will have to be abandoned. The ECM checks the status of the upstream oxygen sensors
during the remainder of the diagnostic, to ensure the air:fuel mixture does not adversely affect the engine idle
speed.
6When the fuel tank pressure sensor detects that the required vacuum has been reached (-800 Pa), the purge
valve is closed and the EVAP system is sealed. The ECM then checks the change in the fuel tank pressure
sensor signal (diminishing vacuum) over a period of time, and if it is greater than expected (after taking into
consideration the compensation factor due to fuel evaporation within the tank, determined earlier in the
diagnostic), a leak in the EVAP system is assumed. If the condition remains, the MIL warning light will be turned
on after two drive cycles.
The decrease in vacuum pressure over the defined period must be large enough to correspond to a hole
equivalent to 1 mm (0.04 in.) diameter or greater, to be considered significant enough to warrant the activation
of an emissions system failure warning.
The diagnostic test is repeated at regular intervals during the drive cycle, when the engine is at idle condition. The
diagnostic test will not be able to be performed under the following conditions:
lDuring EVAP canister purging
lDuring fuelling adaption
lIf excess slosh in the fuel tank is detected (excess fuel vapour will be generated, invalidating the result)

EMISSION CONTROL - V8
DESCRIPTION AND OPERATION 17-2-41
Following the test, the system returns to normal purge operation after the canister vent solenoid opens. Possible
reasons for an EVAP system leak test failure are listed below:
lFuel filler not tightened or cap missing.
lSensor or actuator open circuit.
lShort circuit to vehicle supply or ground.
lEither purge or CVS valve stuck open.
lEither purge or CVS valve stuck shut or blocked pipe.
lPiping broken or not connected.
lLoose or leaking connection.
If the piping is broken forward of the purge valve or is not connected, the engine may run rough and fuelling adaptions
will drift. The fault will not be detected by the leak detection diagnostic, but it will be determined by the engine
management ECM through the fuelling adaption diagnostics.
The evaluation of leakage is dependent on the differential pressure between the fuel tank and ambient atmospheric
pressure, the diagnostic is disabled above altitudes of 9500 ft. (2800 m) to avoid false detection of fuel leaks due to
the change in atmospheric pressure at altitude.
Fuel leak detection system (positive pressure leak detection type) – NAS only
The EVAP system with positive pressure leak detection capability used on NAS vehicles is similar to the standard
system, but also includes a fuel evaporation leak detection pump with integral solenoid valve. It is capable of detecting
holes in the EVAP system down to 0.5 mm (0.02 in.). The test is carried out at the end of a drive cycle, when the
vehicle is stationary and the ignition switch has been turned off. The ECM maintains an earth supply to the Main relay
to hold it on, so that power can be supplied to the leak detection pump.
First a reference measurement is established by passing the pressurised air through a by-pass circuit containing a
fixed sized restriction. The restriction assimilates a 0.5 mm (0.02 in) hole and the current drawn by the pump motor
during this procedure is recorded for comparison against the value to be obtained in the system test. The purge valve
is held closed, and the reversing valve in the leak detection pump module is not energised while the leak detection
pump is switched on. The pressurised air from the leak detection pump is forced through an orifice while the current
drawn by the pump motor is monitored.
Next the EVAP system diagnostic is performed; the solenoid valve is energised so that it closes off the EVAP system's
vent line to atmosphere, and opens a path for the pressurised air from the leak detection pump to be applied to the
closed EVAP system.
The current drawn by the leak detection pump is monitored and checked against that obtained during the reference
measurement. If the current is less than the reference value, this infers there is a hole in the EVAP system greater
than 0.5 mm (0.02 in) which is allowing the positive air pressure to leak out. If the current drawn by the pump motor
is greater than the value obtained during the reference check, the system is sealed and free from leaks. If an EVAP
system leak is detected, the ECM stores the fault in diagnostic memory and the MIL light on the instrument pack is
illuminated.
On NAS vehicles, the ECM works on a 2 trip cycle before illuminating the MIL. On EU-3 vehicles, the ECM works on
a 3 trip cycle before illuminating the MIL.
Following the test, the solenoid valve is opened to normalise the EVAP system pressure and the system returns to
normal purge operation at the start of the next drive cycle. Possible reasons for an EVAP system leak test failure are
listed below:
lFuel filler not tightened or cap missing.
lSensor or actuator open circuit.
lShort circuit to vehicle supply or ground.
lEither purge or solenoid valve stuck open.
lEither purge or solenoid valve stuck shut.
lBlocked pipe or air filter.
lPiping broken or not connected.
lLoose or leaking connection.
If the piping is broken forward of the purge valve or is not connected, the engine may run rough and fuelling adaptions
will drift. The fault will not be detected by the leak detection test, but will be determined by the engine management
ECM through the fuelling adaption diagnostics. This test can be run from TestBook.

EMISSION CONTROL - V8
17-2-42 DESCRIPTION AND OPERATION
Secondary air injection system
When the engine is started, the engine control module checks the engine coolant temperature and if it is below 55°
C, the ECM grounds the electrical connection to the coil of the secondary air injection (SAI) pump relay.
A 12V battery supply is fed to the inertia switch via fuse 13 in the engine compartment fusebox. When the inertia
switch contacts are closed, the feed passes through the switch and is connected to the coil of the Main relay. An earth
connection from the Main relay coil is connected to the ECM. When the ECM completes the earth path, the coil
energises and closes the contacts of the Main relay.
The Main and Secondary Air Injection (SAI) pump relays are located in the engine compartment fusebox. When the
contacts of the Main relay are closed, a 12V battery supply is fed to the coil of the SAI pump relay. An earth connection
from the coil of the SAI pump relay is connected to the ECM. When the ECM completes the earth path, the coil
energises and closes the contacts of the SAI pump relay to supply 12V to the SAI pump via fusible link 2 in the engine
compartment fusebox. The SAI pump starts to operate, and will continue to do so until the ECM switches off the earth
connection to the coil of the SAI pump relay.
The SAI pump remains operational for a period determined by the ECM and depends on the starting temperature of
the engine, or for a maximum operation period determined by the ECM if the target engine coolant temperature has
not been reached in the usual time.
When the contacts of the main relay are closed, a 12V battery supply is fed to the SAI solenoid valve via Fuse 2 in
the engine compartment fusebox.
The ECM grounds the electrical connection to the SAI vacuum solenoid valve at the same time as it switches on the
SAI pump motor. When the SAI vacuum solenoid valve is energised, a vacuum is provided to the operation control
ports on both of the vacuum operated SAI control valves at the exhaust manifolds. The control vacuum is sourced
from the intake manifold depression and routed to the SAI control valves via a vacuum reservoir and the SAI vacuum
solenoid valve.
The vacuum reservoir is included in the vacuum supply circuit to prevent vacuum fluctuations caused by changes in
the intake manifold depression affecting the operation of the SAI control valves.
When a vacuum is applied to the control ports of the SAI control valves, the valves open to allow pressurised air from
the SAI pump to pass through to the exhaust ports in the cylinder heads for combustion.
When the ECM has determined that the SAI pump has operated for the desired duration, it switches off the earth paths
to the SAI pump relay and the SAI vacuum solenoid valve. With the SAI vacuum solenoid valve de-energised, the
valve closes, cutting off the vacuum supply to the SAI control valves. The SAI control valves close immediately and
completely to prevent any further pressurised air from the SAI pump entering the exhaust manifolds.
The engine coolant temperature sensor incurs a time lag in respect of detecting a change in temperature and the SAI
pump automatically enters a 'soak period' between operations to prevent the SAI pump overheating. The ECM also
compares the switch off and start up temperatures, to determine whether it is necessary to operate the SAI pump.
This prevents the pump running repeatedly and overheating on repeat starts.
Other factors which may prevent or stop SAI pump operation include the prevailing engine speed / load conditions.

EMISSION CONTROL - V8
REPAIRS 17-2-47
Sensor - heated oxygen (HO2S) - pre-
catalytic converter
$% 19.22.16
Remove
1.Raise vehicle on a ramp.
2.Release HO
2S multiplug from support bracket.
3.Release HO
2S harness from clip and
disconnect multiplug from HO
2S .
4.Using a 22 mm crow's-foot spanner, remove
HO
2S.
CAUTION: HO
2 sensors are easily damaged
by dropping, excessive heat or
contamination. Care must be taken not to
damage the sensor housing or tip.Refit
1.Clean sensor and exhaust pipe mating
surfaces.
2.If refitting existing sensor, apply anti-seize
compound to sensor threads.
WARNING: Some types of anti-seize
compound used in service are a health
hazard. Avoid skin contact.
NOTE: A new HO
2 sensor is supplied pre-
treated with anti-seize compound.
3.Fit a new sealing washer to HO
2S
4.Fit HO
2S and tighten to 45 Nm (33 lbf.ft).
5. Connect multiplug to HO
2S, and secure to
support bracket and harness clip.
6.Lower vehicle.

EMISSION CONTROL - V8
17-2-48 REPAIRS
Sensor - heated oxygen (HO2S) - post-
catalytic converter
$% 19.22.17
Remove
1.Raise vehicle on ramp.
2.Release HO
2S multiplug from support bracket.
3.Disconnect HO
2S multiplug from harness.
4.Using a 22 mm crowsfoot spanner, remove
HO
2S.
CAUTION: HO2 sensors are easily damaged
by dropping, excessive heat or
contamination. Care must be taken not to
damage the sensor housing or tip.Refit
1.Clean sensor and exhaust pipe mating
surfaces.
2.If refitting existing sensor, apply anti-seize
compound to sensor threads.
WARNING: Some types of anti-seize
compound used in service are a health
hazard. Avoid skin contact.
NOTE: A new HO2 sensor is supplied pre-
treated with anti-seize compound.
3.Fit a new sealing washer to HO
2S
4.Fit HO
2S and tighten to 45 Nm (33 lbf.ft).
5. Connect HO
2S multiplug to harness and fit
harness to bracket.
6.Secure harness to clip.
7.Lower vehicle.

ENGINE MANAGEMENT SYSTEM - TD5
18-1-2 DESCRIPTION AND OPERATION
Engine management component
location - passenger compartment
LHD illustrated
1Diagnostic connector
2Throttle position sensor
3Brake pedal switch