Engine Controls/fuel - 2.4L - Description and Operation: Overview GMC Terrain I

Engine Control Module Description

The Engine Control Module (ECM) interacts with many emission related components and systems, and monitors emission related components and systems for deterioration. OBD II diagnostics monitor the system performance and a diagnostic trouble code (DTC) sets if the system performance degrades. The ECM is part of a network and communicates with various other vehicle control modules.

Malfunction indicator lamp (MIL) operation and DTC storage are dictated by the DTC type. A DTC is ranked as a Type A or Type B if the DTC is emissions related. Type C is a non-emissions related DTC.

The ECM is the control center of the engine controls system. Review the components and wiring diagrams in order to determine which systems are controlled by the ECM.

The ECM constantly monitors the information from various sensors and other inputs, and controls the systems that affect engine performance and emissions. The ECM also performs diagnostic tests on various parts of the system and can turn on the MIL when it recognizes an operational problem that affects emissions. When the ECM detects a malfunction, the ECM stores a DTC. The condition area is identified by the particular DTC that is set. This aids the technician in making repairs.

Modes Of Operation

Normal Mode

During the operation of the TAC system, several modes, or functions, are considered normal. The following modes may be entered during normal operations

1. Minimum pedal value-At key-up, the ECM updates the learned minimum pedal value.
2. Minimum throttle position values-At key-up, the ECM updates the learned minimum throttle position value. In order to learn the minimum throttle position value, the throttle blade is moved to the Closed position.
3. Ice break mode-If the throttle blade is not able to reach a predetermined minimum throttle position, the ice break mode is entered. During the ice break mode, the ECM commands the maximum pulse width several times to the throttle actuator motor in the closing direction.
4. Battery saver mode-After a predetermined time without engine speed, the ECM commands the battery saver mode. During the battery saver mode, the TAC module removes the voltage from the motor control circuits, which removes the current draw used to maintain the idle position and allows the throttle to return to the spring loaded default position.

Reduced Engine Power Mode

When the ECM detects a condition with the TAC system, the ECM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions

1. Acceleration limiting-The ECM will continue to use the accelerator pedal for throttle control, however, the vehicle acceleration is limited.
2. Limited throttle mode-The ECM will continue to use the accelerator pedal for throttle control, however, the maximum throttle opening is limited.
3. Throttle default mode-The ECM will turn OFF the throttle actuator motor, and the throttle will return to the spring loaded default position.
4. Forced idle mode-The ECM will perform the following actions: Limit engine speed to the idle position Ignore the accelerator pedal input.
5. Engine shutdown mode-The ECM will disable fuel and de-energize the throttle actuator.

Scheme 103

CMP Actuator System Operation

The CMP actuator system is controlled by the engine control module (ECM). The ECM sends a signal to a CMP actuator solenoid in order to control the amount of engine oil flow to a Cam Actuator passage. The pressurized engine oil is sent to unseat the locking pin, and to the vane and rotor assembly of the CMP actuator. There are 2 different passages for oil to flow through, a passage for cam advance and a passage for cam retard. The Cam Actuator is attached to a camshaft and is hydraulically operated in order to change the angle of the camshaft relative to crankshaft position (CKP). Engine oil pressure (EOP), viscosity, temperature and engine oil level can have an adverse affect on Cam Actuator performance.

Fuel System Overview

The fuel system is an electronic returnless on-demand design. The returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.

An electric turbine style fuel pump attaches to the fuel tank fuel pump module inside the fuel tank. The fuel pump supplies fuel through the fuel feed pipe to the high pressure fuel pump. The high pressure fuel pump supplies fuel to a variable-pressure fuel rail. Fuel enters the combustion chamber through precision multi-hole fuel injectors. The high pressure fuel pump, fuel rail pressure, fuel injection timing, and injection duration are controlled by the engine control module (ECM).

Fuel Metering Modes of Operation

The ECM monitors voltages from several sensors in order to determine how much fuel to give the engine. The ECM controls the amount of fuel delivered to the engine by changing the fuel injector pulse width. The fuel is delivered under one of several modes.

EVAP System Operation

The evaporative emission (EVAP) control system limits fuel vapors from escaping into the atmosphere. Fuel tank vapors are allowed to move from the fuel tank, due to pressure in the tank, through the EVAP vapor tube, into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent hose and EVAP vent solenoid valve to the atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them. At an appropriate time, the engine control module (ECM) will command the EVAP purge solenoid valve ON, allowing engine vacuum to be applied to the EVAP canister. With the normally open EVAP vent solenoid valve OFF, fresh air is drawn through the vent solenoid valve and the vent hose to the EVAP canister. Fresh air is drawn through the canister, pulling fuel vapors from the carbon. The air/fuel vapor mixture continues through the EVAP purge tube and EVAP purge solenoid valve into the intake manifold to be consumed during normal combustion. The ECM uses several tests to determine if the EVAP system is leaking or restricted.

Electronic Ignition System Description

The electronic ignition system produces and controls a high-energy secondary spark. This spark is used to ignite the compressed air/fuel mixture at precisely the correct time. This provides optimal performance, fuel economy, and control of exhaust emissions. This ignition system uses an individual coil for each cylinder. The ignition coils are mounted in the center of each camshaft cover with short integrated boots connecting the coils to the spark plugs. The driver modules within each ignition coil are commanded ON/OFF by the engine control module (ECM). The ECM primarily uses engine speed, the mass air flow (MAF) sensor signal, and position information from the crankshaft position and the camshaft position sensors. This controls the sequence, dwell, and timing of the spark. The electronic ignition system consists of the following components

Secondary Air Injection System Description

The secondary air injection (AIR) system aids in the reduction of hydrocarbon exhaust emissions during a cold start-up. This occurs when the start-up engine coolant temperature (ECT) is between 5-50°C (41-122°F), and the intake air temperature (IAT) is between 5-60°C (41-140°F). The AIR pump operates 5-60 s after start-up.

The engine control module (ECM) activates the AIR system by simultaneously supplying grounds to the AIR pump and the AIR valve relays. This action closes the relays' internal contacts. The AIR pump and the AIR control solenoid valve/pressure sensor assembly are in turn energized, the pump runs and the control/shut-off valve opens.

The AIR pump sends pressurized fresh air into the pipes/hoses through the open control/shut-off valve, and into the exhaust manifold. The extra air accelerates the catalyst operation, helping it to reach operating temperature faster. The AIR pump remains ON for a short period of time after the control/shut-off valve is commanded OFF. When the AIR pump is commanded OFF it will not run or be activated until the next vehicle start. When the AIR system is inactive, the closed AIR control/shut-off valve prevents air/exhaust flow in either direction.

The AIR system pressure sensor is used to monitor pressure at the AIR control solenoid valve/pressure sensor assembly inlet during the commanded ON/OFF states.

The AIR system includes the following components

1. The AIR pump-The electric AIR pump supplies pressurized, filtered air to the AIR control/shut-off valve. The AIR pump is a turbine type pump that is permanently lubricated and requires no periodic maintenance.
2. The AIR solenoid-The AIR solenoids opens the AIR control/shut-off valve when the solenoid is energized by the AIR solenoid relay.
3. The AIR control solenoid valve/pressure sensor assembly-The AIR control solenoid valve/pressure sensor assembly has a solenoid mounted valve. When the valve is open by the solenoid, pressurized air from the AIR pump flows through the control solenoid valve/pressure sensor assembly and is directed into the exhaust manifold through an outlet pipe.
4. The AIR pressure sensor-The AIR pressure sensor is a part of the AIR control solenoid valve/pressure sensor assembly. The sensor is a 3-wire sensor that measures the AIR system pressure at the AIR control solenoid valve/pressure sensor assembly inlet.
5. The AIR pump relay-The AIR pump relay supplies high current and battery voltage to the AIR pump. The ECM commands the relay ON by supplying a ground to the relay control circuit.
6. The AIR valve relay-The AIR valve relay supplies high current and battery voltage to the AIR solenoid. the ECM commands the relay ON by supplying a ground to the relay control circuit.
7. The pipes and hoses-The AIR system hose carries filtered air from the engine air cleaner to the AIR pump inlet. The pipe/hoses carry the air from the AIR pump to the AIR control solenoid valve/pressure sensor assembly and on to the exhaust manifold.
8. The inlet filter-The AIR system does not have a separate inlet air filter. Filtered air is drawn from the engine air cleaner assembly.

Results of Incorrect Operation

The ECM monitors the secondary air injection (AIR) system for faults during cold start-up operation. When the system's pressure or relay circuits operations vary too far from the predicted values, a DTC will set. Diagnostics detect the following conditions

1. A partially blocked or leaking AIR system
2. A malfunctioning AIR pump
3. A malfunctioning AIR control solenoid valve/pressure sensor assembly
4. A malfunctioning AIR pressure sensor
5. A restricted exhaust system, forward of the catalytic converter
6. A malfunctioning AIR pump and AIR valve relay

The following DTCs set when an AIR system fault is detected

1. DTC P0411-An AIR system insufficient airflow fault condition has been detected.
2. DTC P0412-An AIR valve relay coil circuit fault condition has been detected.
3. DTC P0418-An AIR pump relay coil circuit fault condition has been detected.
4. DTC P2430-An AIR pressure sensor stuck in range fault condition has been detected.
5. DTC P2431-An AIR pressure sensor range/performance fault condition has been detected.
6. DTC P2432-An AIR pressure sensor signal voltage below the minimum range of the sensor fault condition has been detected.
7. DTC P2433-An AIR pressure sensor signal voltage is above the maximum range of the sensor fault condition has been detected.
8. DTC P2440-An AIR system airflow leak fault condition has been detected.
9. DTC P2444-An AIR pump stuck ON fault condition has been detected.