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04/14/2009 NP10-V8JLR: AJ133 5.0-Liter DFI V8 Engine
Technical Training
Relays
Engine Management System
RELAYS
Main Relay
The main Engine Management System (EMS) relay is
not a main power input; it is used to initiate the power-up
and power-down routines within the ECM.
This input comes from the engine junction box (EJB).
When the ignition is turned on 12V is applied to the igni-
tion sense input. The ECM then starts its power-up rou-
tines and turns on the ECM main relay, the main power
to the ECM and its associated system components.
When the ignition is turned OFF, the ECM will maintain
its powered-up state for several seconds (or up to 20
minutes in extreme cases when cooling fans are
required) while it initiates its power-down routine and,
on completion, will turn off the ECM main relay.
The main relay is located in the EJB. The operation of
the main relay is controlled by the ECM, which provides
a ground path for the main relay coil, energizing the
relay and closing the relay contacts.
The main relay supplies battery voltage to the following
engine sensors and actuators:
• Throttle position (TP) sensor (through ECM)
• Fuel injectors
• Ignition coils
• Coil capacitor
• CPS solenoids
• All heated oxygen sensors
• Evaporative emission (EVAP) canister purge valve
• Diagnostic Monitoring of Tank Leakage (DMTL)
Failure Modes
• Relay drive open circuit
• Short circuit to battery voltage or ground
• Component failure
Failure Symptoms
• Engine will not start
Starter Relay
The starter motor relay is located in the EJB. Operation
of the starter motor relay is controlled by the ECM,
which provides a ground path for the relay coil, energiz-
ing the relay and closing the relay contacts. When the
relay contacts are closed, battery voltage is supplied,
through the starter motor relay, to the starter module
solenoid coil.
The starter solenoid is energized and connects the starter
motor with a direct battery feed to operate the starter
motor.
Once the engine has started, the ECM removes the
starter motor relay ground, opening the relay contacts
and terminating the battery feed to the starter solenoid,
which in turn stops the operation of the starter motor.
NOTE:
Diagnose using Jaguar Land Rover approved
diagnostic equipment.
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Fuel Tank Canister Purge ValveEngine Management System
FUEL TANK CANISTER PURGE VALVE
To comply with legislation in fuel evaporative loss, the evaporative emissions loss control system is used on all vehicles.
Its purpose is to minimize the evaporative loss of fuel vapor from the fuel system to the atmosphere. This is achieved by
venting the fuel system through a vapor trap – a canister filled with vapor-absorbing charcoal. The charcoal acts like a
sponge and stores the vapor until the canister is purged under the control of the ECM into the engine for combustion. The
carry-over system uses the DMTL system to check for fuel tank integrity.
The canister is connected with the intake manifold, after the throttle body, via a purge valve. This valve is opened and
closed according to a PWM signal from the ECM. The system does not work properly in the case of leakage or clog-
ging within the system or if the purge valve cannot be controlled.
The canister is purged by drawing clean air through the
charcoal, which carries the hydrocarbons into the engine
where they are combusted. To maintain driveability and
emission control, purging must be closely controlled as a
1% concentration of fuel vapor from the canister in the
air intake may shift the air/fuel ratio by as much as 20%.
Purging must be carried out at regular intervals to regen-
erate the charcoal, since the storage capacity is limited.
The purge function is alternated with the fuel metering
adaptation, as both cannot be active at the same time.
The ECM alters the PWM signal to the purge valve to con-
trol the rate of purging of the canister. The purging of the
canister is done in a controlled manner in order to maintain
the correct stoichiometric air/fuel mixture for the engine.
The ECM also ensures that the canister itself is purged
frequently enough to prevent fuel saturation of the char-
coal, which could lead to an excessive buildup of fuel
vapor (and vapor pressure) in the system, increasing the
likelihood of vapor leaks. Failure Modes
• Valve drive open circuit
• Short circuit to battery voltage or ground
• Valve/pipe work blocked
• Valve stuck open
• Pipe work leaking/disconnected
• Noisy valve
Failure Symptoms
• Engine may possibly stall on return to idle (if valve
stuck open)
• Poor idling quality (if valve stuck open)
• Fuel metering adaptations forced excessively rich if canister is clear with valve stuck open
• Fuel metering adaptations forced excessively lean if canister is saturated with valve stuck open
• Saturation of canister (if valve stuck closed)
PURGE VALVE
AIR FLOWS ENS OR
THROTTLE
FUEL TANK CARBON FILTER
INTAKE
MANIFOLD
NP10V8111
