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Engine
crankshaft is rotating. The voltage input to the relay contact
is via the inertia switch fuel cut off, this is also connected to
the BCM.
The inertia switch supplies 12V to power the fuel pump, the
connection to theBCM provides fuel pump circuit status
information. If the fuel pump relay fails the following symptoms
will be observed:
At Start Up
• If the fuel system pressure has fallen to zero the engine
will not fire.
• If the fuel system pressure has fallen below normal
operating pressure (3.5 bar) the engine may attempt to
fire but will not run normally.
• If the fuel system pressure is normal the engine will fire
and run but will eventually cut out as the fuel pressure
falls, it will not be possible to restart it.
During Driving
If the fuel pump relay fails whilst driving, the engine will lose
power and eventually cut out due to fuel starvation.
The pump relay could fail in the following ways:
• Relay coil short circuit
• Relay coil open circuit
• Relay coil high resistance
• Relay contact stuck open
• Relay contact stuck closed
• Relay contact high resistance
• Relay wiring open circuit
• Relay wiring high resistance
• Relay wiring short circuit to 12V
• Relay wiring short circuit to ground
• ECM not providing ground path
To determine if the fuel pump relay is functioning the following
checks can be carried out:
• Audible check - does the fuel pump run for 2 seconds at
ignition on
• If the answer is negative, check the inertia switch fuel cut
off to ensure it has not been inadvertently triggered
If the fuel pump does not appear to run but the inertia switch
is 'ON' remove the fuel pump relay and test.
Check that theECM is supplying a ground path to the
fuel pump relay winding at ignition on (for 2 seconds) and
during crank. With the fuel pump relay removed, connect
a multimeter between a 12V supply on the vehicle and the
fusebox terminal which corresponds with terminal 85 of the
Version 2.0
Engine Fuel & Management System
fuel pump relay. Switch the ignition on and check the outputs
against the diagram shown on the previous page.
Due toECM the voltage drop across the ECM internal driver
circuit, the voltage measured may be one volt less than battery
voltage.
A/C Clutch Relay
The relay coil is supplied with 12V through fuse 9 in the
engine compartment fusebox and is live when the main relay
is energised. The relay coil ground path is controlled by
the ECM.ECM completes the ground path when anA/C on
request message is received. For further details, refer to AIR
CONDITIONING.
Cooling Fan Relay Unit
The fan control relay unit is connected to theECM by two
wires, these wires supply a ground path to the internal relay
windings. The cooling fan relay receives a 12V supply through
fuse 4 in the engine compartment fusebox. The fan motor is
driven by the output from the internal relays through fuse 4 in
the engine compartment fusebox. To produce a slow fan speed
the ECM provides a ground path to pin 1 of connector EB037
at the relay. To produce a fast fan speed theECM provides a
ground path to pin 2 of connector EB036 at the relay.
EVAP System Purge Valve
The purge valve receives a 12V supply from the main relay via
fuse 1 in the engine compartment fusebox. TheECM controls
the flow through the valve by supplying a PWMground path
which is varied to suit the prevailing conditions. When the
vehicle is being driven theECM will purge the EVAP canister
by opening the purge valve, this allows the vacuum present in
the inlet manifold to draw fuel vapour from the canister into
the cylinders for combustion.
The amount of fuel vapour which enters the cylinders can affect
the overall AFR, therefore theECM must only open the purge
valve when it is able to compensate by reducing fuel injector
duration. The purge valve will operate under the following
conditions:
• ECT sensor reading above 60 °C (140 °F)
• Closed loop fuelling strategy implemented
The HC vapours are converted into carbon dioxide (CO2) and
water (H2O) by the combustion process and the TWC.
When fuel vapour is being removed from the canister, fresh
air is allowed to enter via an automatic one-way valve, this
makes the canister ready for the next 'absorption' phase.
Typical values range from a duty cycle of 0% when the vehicle
is stationary and idling, to 100% when the vehicle is travelling
at speed with under WOT. The mechanical function of the
valve can be tested using a vacuum pump.
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