Discovery II
EMISSION CONTROL - V8
17-2-16 DESCRIPTION AND OPERATION
The ECM connectors and pins which are pertinent to evaporative emission control are listed in the following table:
Fuel Leak Detection System (vacuum type) – NAS only
The advanced evaporative loss control system equipped with a vacuum type, fuel evaporation leak detection
capability is similar to the standard evaporative loss system, but also includes additional components to enable the
engine control module (ECM) to perform a fuel evaporation leak detection test. The system includes an EVAPs
canister and purge valve, and in addition, a canister vent solenoid (CVS) valve and a fuel tank pressure sensor.
The function of the CVS valve is to block the atmospheric vent side of the EVAP canister under the control of the ECM
so that an evaporation system leak check can be performed. The test is carried out when the vehicle is stationary and
the engine is running at idle speed. The system test uses the natural rate of fuel evaporation and engine manifold
depression. Failure of the leak check will result in illumination of the Malfunction Indicator Lamp (MIL).
The fuel evaporation leak detection is part of the On-Board Diagnostics (OBD) strategy and it is able to determine
vapour leaks from holes or breaks greater than 1 mm (0.04 in.) in diameter. Any fuel evaporation system leaks which
occur between the output of the purge valve and the connection to the inlet manifold cannot be determined using this
test, but these will be detected through the fuelling adaption diagnostics.
Connector / Pin No.
Function
Signal type
Control
C0635-23
Main relay output
Output drive
Switch to ground
C0635-24
Leak detection pump motor (NAS vehicles
with positive pressure type EVAP system
leak detection only)
Output drive
Switch to ground
C0636-3
Purge valve drive
Output signal
PWM 12 - 0V
C0636-6
Fuel tank pressure sensor (NAS vehicles
with vacuum type EVAP system leak
detection only)
Ground
0V
C0636-30
Canister vent solenoid (CVS) valve (NAS
vehicles with vacuum type EVAP system
leak detection only) / Fuel leak detection
pump (NAS vehicles with positive pressure
type EVAP system leak detection only)
Output drive
Switch to ground
C0637-9
Fuel tank pressure sensor (NAS vehicles
with vacuum type EVAP system leak
detection only)
Output reference
5V
C0637-12
Analogue fuel level (NAS vehicles with
positive pressure type EVAP system leak
detection only)
Input
Analogue 0 - 5V
C0637-14
Fuel tank pressure sensor (NAS vehicles
with vacuum type EVAP system leak
detection only)
Input signal
Analogue 0 - 5V
C0637-20
MIL "ON"
Output drive
Switch to ground
