303-13B Evaporative Emissions- 4.4L: Description And Operation (page 5 of 6)

 
The charcoal canister is located in a central position, forward of the spare wheel. It is attached at the rear with two bolts 
which screw into the spare wheel carrier. At the front, the canister has two lugs which locate in the parking brake module 
support bracket. 
 
The canister on ROW vehicles has a capacity of 1400 cc (85.4 in

3

). 

 
The canister on NAS vehicles has a capacity of 3000 cc (183 in

3

). 

 
The canister has three ports which allow for the attachment of the atmospheric vent hose, the purge hose and the tank 
vent hose. On NAS vehicles the atmospheric vent hose connection allows for the attachment of the DMTL pump. 
 
The canister contains a bed of activated charcoal or carbon. The charcoal is produced using special manufacturing 
techniques to treat the charcoal with oxygen. The oxygen treatment opens up millions of pores between the carbon atoms 
resulting in a highly porous charcoal with a very large effective surface area which is capable of absorbing large quantities 
of fuel vapor. Once treated the charcoal is known as 'activated' carbon or charcoal. The charcoal canister on NAS 
vehicles uses a higher grade charcoal to meet the requirements of LEV2 emission regulations. 
 

DIAGNOSTIC MONITORING OF TANK LEAKAGE (DMTL) - NAS ONLY 

The DMTL system is a legislative requirement for NAS vehicles. The DMTL system periodically checks the EVAP system 
and the fuel tank for leaks when the ignition is switched off. 
 
The DMTL system comprises the previously described components of the EVAP system with the following additional 
components; a DMTL pump and a DMTL filter. 
 
The DMTL pump is connected to the atmospheric vent of the charcoal canister and incorporates a Positive Temperature 
Co-efficient (PTC) heating element, a normally open valve and a reference orifice. The DMTL pump is only operated 
when the ignition is switched off and is controlled by the ECM. The ECM also monitors the electric air pump operation and 
the normally open valve for faults. 
 
The DMTL filter protects the pump from dust being drawn into the system when the pump is being operated. The filter is 
located on the fuel filler head and is connected to the DMTL pump by a hose. 
 

DMTL Operation 

Item  Part Number 

Description 

1

 -

Charcoal canister atmospheric vent connection (via DMTL pump)

2

 -

DMTL pump

3

 -

Charcoal canister

4

 -

Electrical connector

5

 -

Purge hose connection

6

 -

Charcoal canister tank vent hose connection