Emissions Control: Overview Dodge Avenger II facelift

OPERATION

The switch inputs to the Powertrain Control Module (PCM) have two recognized states; HIGH and LOW. For this reason, the PCM cannot recognize the difference between a selected switch position versus an open circuit, a short circuit, or a defective switch. If the State Display screen shows the change from HIGH to LOW or LOW to HIGH, assume the entire switch circuit to the PCM functions properly. From the state display screen, access either State Display Inputs and Outputs or State Display Sensors.

Scheme 1

Partial zero emission vehicles (PZEV) are equipped with a 2.4L engine with air injection. The air injection system injects air into the exhaust to reduce the emissions during engine warm-up. The air injected into the exhaust will cause the catalytic converter to heat up more quickly. This will improve the emission levels during a cold start. The system consists of an air pump (3), mass air flow sensor (4) and a vacuum check valve (1). The powertrain control module (PCM) controls air pump operation through the air pump relay.

The air injection pump (3) is located in the rear of the engine compartment. The pump is operated by an internal electrical motor and is mounted to a bracket by rubber isolators. An inlet air hose and outlet connecting tube (2) are attached to the air pump.

A mass air flow (MAF) sensor (4) measures the air flow through the air supply hose and works in conjunction with the one way check valve (1). The valve controls the air that is supplied to the exhaust manifold.

During cold start, the air injection system adds a controlled amount of air to the exhaust gases aiding oxidation of hydrocarbons and carbon monoxide in the exhaust stream.

Air is drawn into the pump through a tube that is connected to the mass air flow (MAF) sensor. Airflow is measured by the MAF sensor. A voltage will be produced via the MAF sensor when air is passed through. This voltage correlates to airflow. The amount of voltage (airflow) will determine the amount of fuel that will be added to achieve the goal air/fuel ratio.

Air is then compressed by the air injector pump. It is expelled from the pump into the connecting tube where it reaches the one way check valve and injected into the exhaust manifold.

The one way check valve protects the connecting tube and air pump from hot exhaust gases backing up into the system. Air is allowed to flow through the check valve in one direction only (towards the catalytic convertor).

Scheme 2

The air injection pump (1) is located in the rear of the engine compartment on partial zero emission vehicles (PZEV). The pump is operated by an internal electrical motor and is mounted to a bracket by rubber isolators. An inlet air hose (3) and outlet connecting tube (2) are attached to the air pump. The air pump relay is also located on the pump mounting bracket.

The powertrain control module (PCM) controls air pump operation through the air pump relay. During cold start, air is drawn into the air injector pump through a tube that is connected to the mass air flow (MAF) sensor.

The air is then compressed by the pump and expelled into the connecting tube where it reaches the one way check valve. The one way check valve protects the connecting tube and air pump from hot exhaust gases backing up into the system.

Scheme 3

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1. Remove the engine cover.
2. Disconnect and isolate the negative battery cable.
3. Unlock and disconnect the two PCM wire harness connectors (3).
4. Unlock and disconnect the engine wire harness connector (4).
5. Disengage the engine harness connector retainer (1) from the back of the PCM bracket.
6. Disengage the wire harness retainer (2) from the top of the PCM bracket.
7. Disengage the purge tube retainer (2) from the bottom of the PCM bracket.
8. Unlock and disconnect the two air injection pump assembly wire harness connectors (3).
9. Disengage two wire harness retainers (1) from the back of the PCM bracket and reposition the wire harness.
10. Remove two bolts (2) and the PCM bracket (1) with the PCM attached.
11. To release the connecting tubes from the air pump, squeeze the quick connect fitting as shown in illustration.
12. Disconnect and remove the connecting tube (1) from the air pump (2).
13. Disconnect and remove the air inlet hose (3) from the air pump inlet (2).
14. Raise and support the vehicle. Refer to «HOISTING, STANDARD PROCEDURE»(ref-485472-S37758686622012071300000) .
15. Disengage the oxygen sensor connector retainer (1) from the air pump heatshield.
16. Remove the lower heatshield bolt (2) and reposition the air pump relay (3). NOTE: Air pump not shown in illustration.
17. Lower the vehicle.
18. Remove the upper heatshield bolt (4) and the heatshield (5).
19. Unlock and disconnect the air pump electrical connector (1).
20. Remove the air pump mounting nuts (5) from the bracket (4).
21. Remove the air pump (3) from the bracket (4).

Airflow is measured by the mass air flow (MAF) sensor. The MAF sensor contains a heated ceramic element. The ceramic element changes resistance respectively to changes in temperature. Changes in air flow and air density cause the temperature of the ceramic element to fluctuate. A voltage will be produced via the MAF sensor when air is passed through. This voltage correlates to airflow. The change in resistance varies the signal voltage output to the powertrain control module (PCM).

The one way check valve allows air pumped from the air injection pump to enter the exhaust manifold during cold engine starts only. Air pressure from the air injection pump causes the spring inside the one way check valve to open allowing air to flow into the exhaust system. When the air pump is not operating, the spring closes the valve preventing exhaust gases from reaching the air pump.

DESCRIPTION

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, vapor control valve, one-way check valve and vapor canister.

The ORVR (On-Board Refueling Vapor Recovery) system is used to store and prevent the release into the atmosphere of the 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.

The PCV valve contains a spring loaded plunger. The plunger meters the amount of crankcase vapors routed into the combustion chamber based on intake manifold vacuum.

Scheme 12

When the engine is not operating or during an engine backfire, the spring forces the plunger back against the seat. This prevents vapors from flowing through the valve.

Scheme 13

When the engine is at idle or cruising, high manifold vacuum is present. At these times manifold vacuum is able to completely compress the spring and pull the plunger to the top of the valve. In this position there is minimal vapor flow through the valve.

Scheme 14

During periods of moderate intake manifold vacuum the plunger is only pulled part way back from the inlet. This results in maximum vapor flow through the valve.

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