Emissions Control: Overview RAM Pickup 1500

DESCRIPTION

The Diesel Exhaust Fluid Emissions system uses a Selective Catalytic Reduction (SCR). This is a technology that uses a urea based Diesel Exhaust Fluid (DEF) and a catalytic converter to significantly reduce nitrous oxides (NOx) emissions. The system accomplishes this by injecting small quantities of Diesel Exhaust Fluid (DEF) into the Selective Catalytic Reduction (SCR) where its vaporizes and decomposes to form ammonia and carbon dioxide. The Diesel Exhaust Fluid (DEF) Dosing Control unit is used to control the operation and monitoring of the DEF system. The ammonia is the desired by-product which in conjunction to the SCR Catalyst, converts the NOx to a harmless nitrogen and water. The SCR system is equipped with two NOx Sensors and modules that are used to monitor the efficiency of the SCR Catalyst and DEF system.

The Diesel Exhaust Fluid (DEF) Supply Pump is mounted on the outside left frame rail of the vehicle near the DEF tank. The DEF Supply Pump

1. Has an operating pressure of 9 bar (131 psi)
2. Capable of reverse flow to evacuate system on shut-down
3. Has a serviceable filter
4. Electrically Heated

OPERATION

The Diesel Exhaust Fluid (DEF) Supply Pump has many functions. It's primary purpose is to draw fluid from the tank and build adequate system pressure for dosing into the exhaust. The DEF Dosing Control Unit provides the 12 Volt supply and ground to the pump. The DEF Dosing Control Unit provides a Pulse Width Modulated (PWM) signal to the DEF Supply Pump to control the speed and output of the pump. The DEF Supply Pump has an internal temperature sensor which reports the internal temperature of the DEF Supply Pump to the DEF Dosing Control Unit.

Scheme 5

1. Disconnect both negative battery cables.
2. Disconnect the Diesel Exhaust Fluid (DEF) supply line (1).
3. Disconnect the DEF return line (2).
4. Disconnect the DEF pressure line (3).
5. Disconnect the DEF supply pump harness connector (5).
6. Remove bolts (4) and the DEF supply pump (6).

The Diesel Exhaust Fluid (DEF) Dosing Control Unit controls the function of the Urea's "wet system" (heaters, pump, and injector). The DEF Dosing Control Unit receives a signal from the ECU on when to inject.

The Diesel Exhaust Fluid (DEF) Dosing Control Unit is used to control the operation and monitoring of the Diesel Exhaust Fluid system. The DEF Dosing Control Unit shares information with the ECU over the J1939 Data Link.

Scheme 6

Note. For clarity purposes the Dosing Control Unit mounting bracket was removed from the frame.

Scheme 7

1. Disconnect both negative battery cables.
2. Disconnect the Diesel Exhaust Fluid DEF dosing control unit (2) harness connectors (1). NOTE: For clarity purposes the Dosing Control Unit mounting bracket was removed from the frame.
3. Remove bolts (1) and the DEF dosing control unit from bracket.

The Diesel Exhaust Fluid (DEF) injector is similar to a fuel injector, but modified to be compatible with the Urea fluid. The DEF injector is mounted to the front of the Selective Catalytic Reduction (SCR) catalyst and is designed to operate in a underbody environment.

The Diesel Exhaust Fluid (DEF) Injector is mounted to the decomposition tube at the inlet of the Selective Catalytic Reduction (SCR) Catalyst. The DEF dosing Control Unit sends a Pulse Width Modulated (PWM) signal to the DEF Injector to vary the amount of fluid sprayed into the exhaust stream.

Scheme 8

Scheme 9

Scheme 10

1. Disconnect both negative battery cables.
2. Drain the cooling system. Refer to «Standard Procedure»(ref-457792-S30781673372012030200000) .
3. Disconnect the DEF injector harness connector (1).
4. Disconnect the coolant supply and return lines (2).
5. Disconnect the Diesel Exhaust Fluid (DEF) fluid pressure line (1).
6. Remove bolts and the DEF injector (1) from the Selective Catalytic Reduction (SCR) catalyst (2).

Scheme 11

Scheme 12

1. Install a new Diesel Exhaust Fluid (DEF) injector gasket (1).
2. Install the DEF injector (1) onto Selective Catalytic Reduction (SCR) catalyst (2). CAUTION: Failure to follow the installation and tightening procedure may result in damage to the DEF injector housing.
3. Using the sequence shown in illustration, install bolts finger tight.
4. Using the sequence shown in illustration, tighten bolts to 11 N.m (97 in. lbs.) .
5. Connect the DEF fluid pressure line (1).
6. Connect the coolant supply and return lines (2).
7. Connect the DEF injector harness connector (1).
8. Fill the cooling system. Refer to «Standard Procedure»(ref-457792-S30781673372012030200000) .
9. Connect both negative battery cables.

The Diesel Exhaust Fluid (DEF) tank is mounted to the frame of the vehicle on the left side and is equipped with

1. Engine Coolant Heat Exchanger
2. Level Sensor
3. Temp Sensor
4. Vent Valve
5. Fluid Limit Vent Valve

Scheme 13

Scheme 14

Scheme 15

Scheme 16

Scheme 17

Scheme 18

Scheme 19

Scheme 20

Scheme 21

Scheme 22

Scheme 23

1. Disconnect both negative battery cables.
2. Drain the cooling system. Refer to «Standard Procedure»(ref-457792-S30781673372012030200000) .
3. Disconnect the coolant lines (1 and 2) going to Diesel Exhaust Fluid (DEF) tank.
4. Remove push pin (4) and unclip coolant lines bracket (3) from frame rail.
5. Disconnect the fill tube vent line (2) from fluid limit vent valve (1).
6. Disconnect the fill tube (1) from DEF tank (2).
7. Disconnect the DEF supply/return line heater harness connector (1).
8. Disconnect the DEF supply (2) and return (3) lines from the DEF supply pump.
9. Position a transmission jack under DEF tank.
10. Remove bolts (1) and partially lower the DEF tank (2).
11. Disconnect the DEF tank level/temperature sensor harness connector (1).
12. Disconnect the wire harness loom retainers (2) from bracket.
13. Disconnect the coolant control valve harness connector (1).
14. Remove the DEF tank.
15. Disconnect the coolant supply (1) and return lines (2) from DEF tank.
16. Disconnect the DEF supply (3) and return (4) lines from DEF tank.
17. Disconnect the coolant lines (5) at routing clip (6).
18. Disconnect DEF lines (7) at routing clip (8) and remove lines.
19. Remove bolt (1) and the coolant control valve assembly (2).
20. Remove nut (2) and the front tank strap (1).
21. Remove nut (2) and the rear tank strap (1).

The Diesel Exhaust Fluid (DEF) pump filter is a 10-micron filter designed to prevent foreign objects from entering the dosing system. Debris can cause permanent damage and premature failure to either the aftertreatment diesel exhaust fluid pump or the aftertreatment diesel exhaust fluid injector. The aftertreatment diesel exhaust fluid pump filter is a maintenance item.

Scheme 24

Scheme 25

1. Disconnect both negative battery cables.
2. Clean the Diesel Exhaust Fluid (DEF) pump to remove contamination or debris by the fluid filter.
3. Remove the DEF filter cap (1).
4. Pull out the old DEF filter element from DEF supply pump and discard.
5. Inspect the DEF filter cap and rubber seal for damage or cracks.

The Diesel Exhaust Fluid (DEF) Tank Level Sensor and the Diesel Exhaust Fluid Sensor (DEF) Tank Temperature Sensor are a combination sensor used to measure the fluid level of the tank and the temperature of the fluid in the DEF tank.

The Diesel Exhaust Fluid (DEF) Tank Level Sensor and Diesel Exhaust Fluid (DEF) Tank Temperature Sensor are a combined sensor used to measure the level and temperature of the fluid in the DEF Tank. Though combined, the level sensor and the temperature sensor operate independent of each other. Both sensors operate as a two wire 5-Volt sensor. The DEF Tank Level Sensor is a 14 point magnetic reed switch sensor. The DEF Tank Temperature Sensor is a negative temperature coefficient sensor.

Scheme 26

1. Disconnect both negative battery cables.
2. Remove Diesel Exhaust Fluid (DEF) tank. Refer to «TANK, Diesel Exhaust Fluid, Removal»(ref-457800-S03029686772012030200000) .
3. Using the DEF Module Lock Ring Wrench (special tool #10189, Wrench, DEF Module Lock Ring) (1), remove the lock ring (3) from the DEF tank (4).
4. Remove the level/temperature sensor (2) from DEF tank (4).
5. Remove and discard O-ring seal.

Scheme 27

Scheme 28

1. Clean O-ring sealing surfaces.
2. Install a new O-ring seal (1) onto the Diesel Exhaust Fluid (DEF) tank (2).
3. Install the DEF tank level/temperature sensor (1) into tank.
4. Using the DEF Module Lock Ring Wrench (special tool #10189, Wrench, DEF Module Lock Ring) (1), install the lock ring (3) onto the DEF tank (4) and lock in place.
5. Install the DEF tank. Refer to «TANK, Diesel Exhaust Fluid , Installation»(ref-457800-S22113021672012030200000) .
6. Connect both negative battery cables.

The Diesel Exhaust Fluid (DEF) supply line supplies fluid from the tank to the pump and has connectors similar to fuel lines. The line also incorporates a heater to keep the DEF fluid from freezing. The DEF supply and return line heater also share the same wire harness connector.

Each of the Diesel Exhaust Fluid (DEF) system hoses has a built in heater to warm the fluid in the line. The line heater has power supplied to it via the DEF Line Relay which is controlled by the DEF Dosing Control Module. The Line heater circuits are monitored on the return side of the circuit.

The Diesel Exhaust Fluid (DEF) pressure line supplies fluid from the pump to the injector and has connectors similar to fuel lines. The line also incorporates a heater to keep the DEF fluid from freezing.

Each of the Diesel Exhaust Fluid (DEF) system hoses has a built in heater to warm the fluid in the line. The line heater has power supplied to it via the DEF Line Relay which is controlled by the DEF Dosing Control Module. The Line heater circuits are monitored on the return side of the circuit.

Scheme 29

Scheme 30

1. Disconnect both negative battery cables.
2. Disconnect the Diesel Exhaust Fluid (DEF) pressure line (1) heater harness connector (2).
3. Disconnect the DEF pressure line (1) at the DEF supply pump. Refer to «STANDARD PROCEDURE - QUICK-CONNECT FITTINGS»(ref-457834-S33306886662012030200000) .
4. Disconnect the DEF pressure line retainer at the frame rail and coolant lines (1).
5. Disconnect and remove the DEF pressure line (2) at DEF injector (3). Refer to «STANDARD PROCEDURE - QUICK-CONNECT FITTINGS»(ref-457834-S33306886662012030200000) .

The Diesel Exhaust Fluid (DEF) return line allows unused DEF fluid to be pumped back into the tank and has connectors similar to fuel lines. The line also incorporates a heater to keep the DEF fluid from freezing. The DEF supply and return line heater also share the same wire harness connector.

Each of the Diesel Exhaust Fluid (DEF) system hoses has a built in heater to warm the fluid in the line. The line heater has power supplied to it via the DEF Line Relay which is controlled by the DEF Dosing Control Module. The Line heater circuits are monitored on the return side of the circuit.

The Diesel Exhaust Fluid (DEF) Pressure Sensor is housed inside the DEF Supply Pump that monitors supplied pressure to the DEF Injector. The DEF Pressure Sensor is not a serviceable item as it is part of the DEF Supply Pump.

The Diesel Exhaust Fluid (DEF) Pressure Sensor is a three wire sensor, housed inside the DEF Supply Pump that monitors supplied pressure to the DEF Injector. The DEF Dosing Control Unit provides a 5-Volt supply and ground to the DEF Pressure Sensor. The sensor provides a signal to the DEF Dosing Control Unit on the DEF Pressure Sensor Signal circuit. This DEF Pressure Sensor Signal voltage changes, based on the diesel exhaust fluid pressure supplied by the DEF Supply Pump. The DEF Dosing Control Unit uses this information to vary pump speed and maintain the 130 psi (9 bar) pressure needed for proper DEF Injection.

The Pre-NOx sensor is mounted at the inlet of Selective Catalytic Reduction (SCR) Catalyst and measures incoming NOx gases. The Post-NOx sensor is mounted at the rear outlet of Selective Catalytic Reduction (SCR) Catalyst and measures outgoing NOx gases.

There are two NOx modules and sensors used in the DEF fluid system, upstream and downstream. Both operate similarly to a wide band O2 sensor. The sensors are zirconium-based, multi-layer sensors with oxygen pumps. The NOx modules communicate the amount of NOx to the ECM over the J1939 communication bus. The upstream module is located on the right frame rail and the sensor is at the front of the Diesel Particulate Filter (DPF). The upstream module and sensor are used by the ECM to monitor NOx entering the catalyst. By comparing the inlet sensor to the outlet sensor, SCR efficiency can be determined by the ECM.

Scheme 31

Scheme 32

Scheme 33

1. Disconnect both negative battery cables.
2. Remove nuts (1) and the NOx sensor module cover (3).
3. Disconnect the NOx sensor wire harness retainer (2).
4. Disconnect the NOx sensor harness connector (2).
5. Remove nuts (1) and the NOx sensor module (3).
6. Remove the NOx sensor (1) from the Diesel Oxidation Catalytic/Diesel Particulate Filter (DOC/DPF) (2).

Scheme 34

Scheme 35

1. Disconnect both negative battery cables.
2. Disconnect the NOx sensor module harness connector (3).
3. Remove nuts (1) and the NOx module (2).
4. Disconnect the wire harness retainers.
5. Remove the NOx sensor (1) from the Selective Catalytic Reduction (SCR) catalyst (2).

The ambient temperature sensor monitors the underbody temperature surrounding the Diesel Exhaust Fluid (DEF) supply pump and communicates to the ECU when the DEF system heaters are required.

Scheme 36

1. Disconnect both negative battery cables.
2. Clean the area surrounding the Diesel Exhaust Fluid (DEF) ambient air temperature sensor
3. Disconnect and remove the DEF ambient temperature sensor (1) from the harness connector (2).

The Diesel Exhaust Fluid (DEF) Relay receives a power signal from the DEF Dosing Control Unit based on ambient air temperature to thaw the DEF fluid lines if frozen. The DEF Relay also sends power to the DEF Engine Coolant Control Valve to allow warm engine coolant to thaw the DEF fluid inside the tank.

The Diesel Exhaust Fluid (DEF) Engine Coolant Control Valve is used to allow engine coolant to being circulated in the DEF tank or blocked depending on ambient air temperature.

The Diesel Exhaust Fluid (DEF) Tank has an internal heating coil to help eliminate freezing of DEF. The DEF Dosing Control Unit monitors the temperature of the DEF in the tank. When it is determined that the DEF needs to be heated, the DEF Dosing Control Unit opens the DEF Engine Coolant Valve and allows warm engine coolant to circulate through the heating coil to warm the DEF in the tank.

The Crankcase Pressure (CP) Sensor (5) is mounted on the valve cover (4). The CP sensor monitors crankcase pressure that builds up as the result of combustion gas blow-by. The Powertrain Control Module (PCM) uses data from the CP sensor to determine the condition of the crankcase breather (ventilation) filter. The PCM can also determine if a crankcase breather (ventilation) filter is present.

The CCV system reroutes crankcase ventilation (blow-by) gases from the breather assembly back into the engine intake airflow to be used for combustion. The crankcase ventilation system uses a coalescing filter (2) which captures and filters crankcase blow-by gases and then returns oil directly to the sump.

Scheme 37

The Closed Crankcase Ventilation System (CCV) consists of several parts to make it functional. One part is the breather element (1). The breather element (1) is serviceable and prevents oil mist from entering the discharge tube of the CCV system. The breather element (1) should be replaced at 67,500 mile intervals.

Crankcase gasses travel into the breather cavity under the breather cover where they pass through a filtering media (serviceable maintenance component) which separates the oil from the crankcase gasses. The oil drains back into the engine block through two hoses (2) on the left side of the engine.

The crankcase gasses are directed through the Crankcase Depression Regulator (CDR) valve which allows the system to maintain a constant positive pressure in the crankcase. The CDR valve is a non-serviceable component located on the underside of the breather cover. Clean crankcase gasses flow from the CDR valve into the fresh air side of the turbocharger compressor.

The EGR Temperature Sensor (1) is located on the EGR crossover tube (6) near the EGR valve.

Scheme 38

The EGR temperature sensor is a negative temperature coefficient thermistor used to measure the temperature of the EGR gas flow after it exits the EGR cooler.

The Powertrain Control Module (PCM) supplies 5 volts to the EGR temperature signal circuit. To determine the temperature of the EGR gas flow, the PCM monitors the change in voltage caused by changes in the resistance of the sensor. The PCM uses the exhaust gas recirculation temperature value for the engine protection system, and also for engine emissions control.

Depending on engine displacement, either one or two EVAP canisters may be used. Also depending on vehicle model and fuel tank size, the canisters may be mounted either vertically or horizontally.

The ESIM (Emission System Integrity Monitor) switch is mounted to the EVAP canister. The NVLD system is no longer used on any engine.

The EVAP canister(s) are filled with granules of an activated carbon mixture. Fuel vapors entering the EVAP canisters are absorbed by the charcoal granules.

Fuel tank pressure vents into the EVAP canisters. Fuel vapors are temporarily held in the canisters until they can be drawn into the intake manifold. The duty cycle EVAP canister purge solenoid allows the EVAP canisters to be purged at predetermined times and at certain engine operating conditions.

Scheme 39

A single, vertically mounted EVAP canister (1) is used with Type 1. The ESIM (Emission System Integrity Monitor) switch (3) is mounted to the canister.

1. Raise and support vehicle.
2. If equipped, remove necessary skid plates. Certain models, equipped with a certain fuel tank size, may require the removal of the fuel tank skid plate and/or the transfer case skid plate to gain access to the EVAP canister(s).
3. Disconnect electrical wiring connector from ESIM switch (3).
4. Disconnect vapor line (6) from ESIM switch.
5. Disconnect quick-connect vapor line (5) from canister.
6. Remove canister mounting bracket bolt. This is located below and near the ESIM switch.
7. Pull canister from mounting bracket while guiding two canister locating pins from mounting bracket.

Scheme 40

A single, vertically mounted EVAP canister (1) is used with Type 2. The ESIM (Emission System Integrity Monitor) switch (2) is mounted to the canister.

1. Raise and support vehicle.
2. If equipped, remove necessary skid plates. Certain models, equipped with a certain fuel tank size, may require the removal of the fuel tank skid plate and/or the transfer case skid plate to gain access to the EVAP canister(s).
3. Disconnect electrical wiring connector from ESIM switch (3).
4. Disconnect vapor line (7) from ESIM switch.
5. Disconnect quick-connect vapor line (5) at canister.
6. Remove canister mounting bracket bolt (6).
7. Pull canister from mounting bracket while guiding two canister locating pins from mounting bracket.

Scheme 41

Dual, vertically mounted EVAP canisters (1) and (4) are used with Type 3. The ESIM (Emission System Integrity Monitor) switch (2) is mounted to the main canister (1). Canister (4) is considered a secondary canister.

1. Raise and support vehicle.
2. If equipped, remove necessary skid plates. Certain models, equipped with a certain fuel tank size, may require the removal of the fuel tank skid plate and/or the transfer case skid plate to gain access to the EVAP canister(s).
3. Disconnect electrical wiring connector from ESIM switch (3).
4. Disconnect vapor line (9) from ESIM switch.
5. Disconnect quick-connect vapor line (7) at main canister.
6. Remove canister mounting bracket bolt (8).
7. Pull canister from mounting bracket while guiding two canister locating pins from mounting bracket.
8. To remove the secondary canister (4), remove mounting bolt. Pull canister from mounting bracket while guiding two canister locating pins (6) from mounting bracket.

Scheme 42

Dual, horizontally mounted EVAP canisters (1) and (7) are used with Type 4. The ESIM (Emission System Integrity Monitor) switch (3) is mounted to the main, primary canister (1). Canister (7) is considered a secondary canister.

1. Raise and support vehicle.
2. If equipped, remove necessary skid plates. Certain models, equipped with a certain fuel tank size, may require the removal of the fuel tank skid plate and/or the transfer case skid plate to gain access to the EVAP canister(s).
3. Disconnect electrical wiring connector from ESIM switch (4).
4. Disconnect vapor line (5) from ESIM switch.
5. Disconnect quick-connect vapor line (8) at main canister.
6. Remove primary canister mounting bracket nut (9).
7. Pull canister from mounting bracket while guiding two canister locating pins from mounting bracket.
8. To remove the secondary canister (7), remove mounting nut (6). Pull canister from mounting bracket while guiding two canister locating pins from mounting bracket.

Type-1 Canisters

A single, vertically mounted EVAP canister (1) is used with Type 1. The ESIM (Emission System Integrity Monitor) switch (3) is mounted to the canister.

1. Two locating pins are located at rear of canister. Push these two pins into canister mounting bracket.
2. Install canister mounting bracket bolt. This is located below and near the ESIM switch.
3. Connect quick-connect vapor line (5) to canister.
4. Connect vapor line (6) to ESIM switch.
5. Connect electrical wiring connector to ESIM switch (3).
6. If equipped, install necessary skid plates.
7. All vapor/vacuum lines and hoses must be firmly connected. Also check the vapor/vacuum lines at the EVAP canister purge solenoid for damage or leaks. If a leak is present, a Diagnostic Trouble Code (DTC) may be set.
8. Lower vehicle.

Type-2 Canisters

A single, vertically mounted EVAP canister (1) is used with Type 2. The ESIM (Emission System Integrity Monitor) switch (2) is mounted to the canister.

1. Two locating pins are located at rear of canister. Push these two pins into canister mounting bracket.
2. Install canister mounting bracket bolt (6).
3. Connect quick-connect vapor line (5) to canister.
4. Connect vapor line (7) to ESIM switch.
5. Connect electrical wiring connector to ESIM switch (3).
6. If equipped, install necessary skid plates.
7. All vapor/vacuum lines and hoses must be firmly connected. Also check the vapor/vacuum lines at the EVAP canister purge solenoid for damage or leaks. If a leak is present, a Diagnostic Trouble Code (DTC) may be set.
8. Lower vehicle.

Type-3 Canisters

Dual, vertically mounted EVAP canisters (1) and (4) are used with Type 3. The ESIM (Emission System Integrity Monitor) switch (2) is mounted to the main canister (1). Canister (4) is considered a secondary canister.

1. Push secondary canister (4) into mounting bracket while guiding two canister locating pins (6) into mounting bracket. Install mounting bolt.
2. Push main, primary canister (1) into mounting bracket while guiding two canister locating pins into mounting bracket.
3. Install main canister mounting bracket bolt (8).
4. Connect quick-connect vapor line (7) to main canister.
5. Connect vapor line (9) to ESIM switch.
6. Connect electrical wiring connector to ESIM switch (3).
7. If equipped, install necessary skid plates.
8. All vapor/vacuum lines and hoses must be firmly connected. Also check the vapor/vacuum lines at the EVAP canister purge solenoid for damage or leaks. If a leak is present, a Diagnostic Trouble Code (DTC) may be set.
9. Lower vehicle.

Type-4 Canisters

Dual, horizontally mounted EVAP canisters (1) and (7) are used with Type 4. The ESIM (Emission System Integrity Monitor) switch (3) is mounted to the main, primary canister (1). Canister (7) is considered a secondary canister.

1. Position two secondary canister locating pins into mounting bracket. Install mounting nut (6).
2. Position two primary canister locating pins into mounting bracket.
3. Install primary canister mounting bracket nut (9).
4. Connect quick-connect vapor line (8) to main canister.
5. Connect vapor line (5) to ESIM switch.
6. Connect electrical wiring connector to ESIM switch (4).
7. If equipped, install necessary skid plates.
8. All vapor/vacuum lines and hoses must be firmly connected. Also check the vapor/vacuum lines at the EVAP canister purge solenoid for damage or leaks. If a leak is present, a Diagnostic Trouble Code (DTC) may be set.
9. Lower vehicle.

The plastic fuel fill cap is a threaded/quarter turn onto the end of the fuel filler tube. Its purpose is to retain vapors and fuel in the fuel tank.

The loss of any fuel vapor out of fuel filler tube is prevented by the use of pressure-vacuum fuel fill cap. Relief valves inside the cap will release fuel tank pressure at predetermined pressures. Fuel tank vacuum will also be released at predetermined values. This cap must be replaced by a similar unit if replacement is necessary. This is in order for the system to remain effective.

The ORVR (On-Board Refueling Vapor Recovery) system consists of a unique fuel tank, flow management valve, fluid control valve, one-way check valve and vapor canister.

The ORVR (On-Board Refueling Vapor Recovery) system is used to remove excess fuel tank vapors. This is done while the vehicle is being refueled.

Fuel flowing into the fuel filler tube (approx. 1" I.D.) creates an aspiration effect drawing air into the fuel fill tube. During refueling, the fuel tank is vented to the EVAP canister to capture escaping vapors. With air flowing into the filler tube, there are no fuel vapors escaping to the atmosphere. Once the refueling vapors are captured by the EVAP canister, the vehicle's computer controlled purge system draws vapor out of the canister for the engine to burn. The vapor flow is metered by the purge solenoid so that there is no, or minimal impact on driveability or tailpipe emissions.

As fuel starts to flow through the fuel fill tube, it opens the normally closed check valve and enters the fuel tank. Vapor or air is expelled from the tank through the control valve and on to the vapor canister. Vapor is absorbed in the EVAP canister until vapor flow in the lines stops. This stoppage occurs following fuel shut-off, or by having the fuel level in the tank rise high enough to close the control valve. This control valve contains a float that rises to seal the large diameter vent path to the EVAP canister. At this point in the refueling process, fuel tank pressure increases, the check valve closes (preventing liquid fuel from spiting back at the operator), and fuel then rises up the fuel filler tube to shut off the dispensing nozzle.

Scheme 43

The duty cycle EVAP canister purge solenoid (1) is located in the engine compartment below and near the battery.

1. Carefully pull the solenoid assembly straight up from the tongue-type bracket without bending the two vapor lines.
2. Disconnect electrical wiring connector (2) at solenoid.
3. Disconnect vapor line quick-connect fitting (3) at solenoid.
4. Disconnect vapor line quick-connect fitting (4) at solenoid.

The following procedure has been established to assist technicians in the field with enabling and running OBD II Monitors. The order listed in the following procedure is intended to allow the technician to effectively complete each monitor and to set the CARB Readiness Status in the least time possible.

Note. Once the monitor run process has begun, do not turn off the ignition. By turning the ignition key off, monitor enabling conditions will be lost. EVAP Monitor runs after key off. By performing a Battery Disconnect, or Selecting Erase DTCs, the CARB Readiness and all additional OBD II information will be cleared.

The PCM is responsible for efficiently coordinating the operation of all the emissions-related components. The PCM is also responsible for determining if the diagnostic systems are operating properly. The software designed to carry out these responsibilities is call the "Task Manager".

The Task Manager determines when tests happen and when functions occur. Many of the diagnostic steps required by OBD II must be performed under specific operating conditions. The Task Manager software organizes and prioritizes the diagnostic procedures. The job of the Task Manager is to determine if conditions are appropriate for tests to be run, monitor the parameters for a trip for each test, and record the results of the test. Following are the responsibilities of the Task Manager software

1. Test Sequence
2. MIL Illumination
3. Diagnostic Trouble Codes (DTCs)
4. Trip Indicator
5. Freeze Frame Data Storage
6. Similar Conditions Window