AIR INDUCTION SYSTEM
All engines use the same basic air induction system. Remote air filter (with airflow sensor) is ducted to a plenum-mounted throttle body.
COMPUTERIZED ENGINE CONTROLS
All models use a Multiport Fuel Injection (MFI) system. This system consists of sensors which detect engine conditions. The Electronic Control Module (ECM) controls the system based on signals from these sensors, and from actuators which operate under the control of the ECM. ECM controls fuel injection, idle speed, ignition timing, emission controls and some other functions.
Fuel Injection Control
ECM controls fuel injector timing and pulse width based on sensor inputs. ECM uses the Crankshaft Position (CKP) sensor to determine when to pulse each injector. ECM uses engine coolant temperature, intake air temperature, airflow and throttle position information to calculate injector pulse width. Each fuel injector is pulsed once for each cylinder for every 2 crankshaft rotations. During cranking, all injectors are pulsed simultaneously until engine starts. During engine operation, each injector is sequentially pulsed individually.
Engine Idle Speed Control
ECM controls idle speed based on engine load and temperature. Engine idle speed is kept at the optimum speed by controlling amount of air that by-passes throttle valve. ECM controls Idle Speed Control (ISC) motor to keep the engine running at a pre-set idle target speed in accordance with the engine temperature and power steering (if equipped) and air conditioning loads. When engine load increases because of power steering and/or air conditioning activation, the ECM will increase engine idle speed to avoid fluctuations in engine speed.
Ignition Timing Control
The ignition power transistor, located in the ignition primary circuit, turns on and off to control the primary current flow to the ignition coil. This controls the ignition timing in order to provide the optimum ignition timing with respect to the engine operation conditions. The ignition timing is determined by the ECM from the engine speed, intake air volume, engine coolant temperature and atmospheric pressure inputs.
Other Control Functions
The ECM also controls the fuel pump relay, A/C compressor clutch operation, radiator and condenser fan operation and speeds, evaporative emission purge control and EGR solenoid operation.
Note. Components are grouped into 2 categories. First category is INPUT DEVICES , which are components that control or produce signals monitored by the ECM. The second category is OUTPUT SIGNALS , which are components controlled by the ECM.
INPUT DEVICES
The ECM controls various output devices based upon signals received from input devices. These devices include sensors, switches, and circuits (such as an RPM reference signal from the ignition coil). Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine input usage on a specific model, see appropriate diagram in WIRING DIAGRAMS article. Available input signals include the following
A/C Switch
When the air conditioner switch is turned on, a signal is sent to the ECM. The ECM then engages the compressor clutch and adjusts the Idle Air Control (IAC) servo to maintain optimum idle speed.
Acceleration Sensor (Accent, Elantra & Tiburon)
This sensor is located on bracket on left front strut tower. When accelerating or driving on a rough road, ECM uses the accelerator sensor input signal to avoid false misfire detection.
Camshaft Position (CMP) Sensor
On Accent, Camshaft Position (CMP) sensor is located at the back of the cylinder head, next to the ignition coils. On Elantra and Tiburon, the CMP sensor is located at the front of the cylinder head, near the No. 1 fuel injector. CMP sensor senses TDC point of cylinder No. 1 in its compression stroke. This signal is fed to ECM to determine fuel injector sequence starting point.
Crankshaft Position (CKP) Sensor
Crankshaft Position (CKP) sensor is located at the left side of the block, near the flywheel. ECM use voltage signal from CKP sensor to detect engine RPM and crankshaft position.
Engine Coolant Temperature (ECT) Sensor
Engine Coolant Temperature (ECT) sensor is located on thermostat housing. ECT sensor is a thermistor whose resistance decreases as engine coolant temperature increases. ECM uses ECT sensor information for controlling fuel enrichment when engine is cold.
Fuel Tank Pressure (FTP) Sensor
On Accent, Fuel Tank Pressure (FTP) sensor is located on fuel filler neck. On all other models, FTP sensor is located between fuel tank and rear suspension crossmember. FTP sensor is a pressure-sensitive variable resistor. It measures fuel tank pressure changes, monitoring fuel tank for leaks. It is used to close the evaporative system, and observes tank pressure respectively with canister close valve.
Heated Oxygen Sensor (HO2S)
All vehicles except Sonata 2.5L are equipped with 2 Heated Oxygen Sensors (HO2S). Sonata 2.5L is equipped with 4 sensors, one pair for each bank. On all models, a front HO2S is located in the exhaust manifold in front of the catalytic converter. The front HO2S determines whether the air fuel mixture is too rich or too lean. ECM uses front HO2S to control air fuel mixture and fuel delivery time. A rear HO2S is located after the catalytic converter. ECM compares signals from both sensors and calculates catalytic converter efficiency. On all models except Sonata 2.5L, HO2S output voltage ranges from 0-0.1 volt (lean) to about 0.8-1.0 volt (rich). On Sonata 2.5L, HO2S output voltage ranges from 0-0.2 volt (lean) to about 4.5-5.0 volts (rich). HO2S heater is used to bring sensor to operating temperature as quickly as possible for optimum operation under all engine operating conditions.
Idle Position Switch (Sonata 2.4L)
Idle switch is included within the Throttle Position Switch (TPS). Idle switch signals ECM whether accelerator pedal is depressed or not. Idle switch is normally closed at idle and open when accelerator is off idle position.
Intake Air Temperature (IAT) Sensor
Intake Air Temperature (IAT) sensor measures temperature of intake air, and sends a signal to ECM. IAT sensor is a variable-resistor type airflow sensor. As intake air temperature decreases IAT sensor output voltage to ECM increases. On Sonata 2.4L, sensor is located in intake air housing with MAF sensor. On all other models, sensor is located in air cleaner housing. ECM uses IAT sensor signal to control fuel delivery. When air temperature is cold, ECM enriches fuel mixture by increasing injector pulse width. ECM will decrease injector pulse width when air temperature is warm.
Knock Sensor (KS)
Knock sensor is mounted on engine block. Sensor detects knocking condition/vibration from engine. KS is a piezo electric element that converts vibration into a voltage signal which is then sent to ECM. ECM compares KS and rough road (acceleration) sensor inputs to detect true engine knock. If ECM determines that true engine knock is occurring, ECM will retard timing until knock is suppressed.
Mass Airflow (MAF) Sensor
MAF sensor is a hot-film type airflow sensor mounted within the intake duct between the air cleaner and throttle body. Mass airflow rate is measured by detecting changes in the temperature of the hot-film probe, and comparing it to changes in sensor resistance. ECM uses MAF signal to determine basic fuel injection pulse width and ignition timing.
Manifold Absolute Pressure (MAP) Sensor (Sonata 2.4L)
Manifold absolute pressure sensor converts intake manifold pressure into a voltage signal. ECM uses MAP sensor signal to verify operation of Exhaust Gas Recirculation (EGR) system.
Power Steering Pressure (PSP) Switch
The PSP switch closes in response to an increase in power steering fluid pressure (load condition). With the switch closed, a monitored voltage circuit supplied by the ECM is pulled low to vehicle ground through switch. The ECM then sends a signal to the ISC actuator to adjust idle speed to compensate for increased engine load.
Throttle Position (TP) Sensor
The TP sensor is a potentiometer connected to the throttle valve shaft. As throttle opening changes, the sensor sends a voltage signal to ECM. The ECM uses this signal to calculate fuel injection duration.
Transaxle Range Switch (A/T)
The Transaxle Range (TR) switch informs the ECM when the transaxle is in Neutral or Park. ECM determines automatic transmission load, and signals the Idle Air Control (IAC) servo to maintain optimum idle speed.
Vehicle Speed Sensor (VSS)
VSS is located within the speedometer assembly and uses a reed switch to sense speedometer gear revolutions from the transaxle. VSS converts transaxle gear revolutions into pulse signals which are sent to the ECM.
OUTPUT SIGNALS
Note. Vehicles are equipped with different combinations of computer-controlled components. Not all components listed are used on every vehicle. For theory and operation on each output component, refer to system indicated after component.
The ECM processes information from input sensors and sends appropriate control signals to the following engine controls
A/C Clutch
See A/C CLUTCH under MISCELLANEOUS CONTROLS.
A/C Condenser Fan Relay
See appropriate MANUAL A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING SERVICE & REPAIR.
Blower Motor Relay
See appropriate HEATER SYSTEMS article in AIR CONDITIONING & HEATING SERVICE & REPAIR.
Canister Close Valve
See EVAPORATIVE CONTROL under EMISSION SYSTEMS.
Canister Purge Valve
See EVAPORATIVE CONTROL under EMISSION SYSTEMS.
EGR Control Solenoid Valve
See EXHAUST GAS RECIRCULATION (EGR) CONTROL under EMISSION SYSTEMS.
Engine Control Relay
See SYSTEM & COMPONENT TESTING article.
Fuel Injectors
See FUEL CONTROL under FUEL SYSTEM.
Fuel Pump Relay
See FUEL DELIVERY under FUEL SYSTEM.
Idle Speed Control (ISC) Actuator
See IDLE SPEED under FUEL SYSTEM.
Malfunction Indicator Light (MIL)
See MALFUNCTION INDICATOR LIGHT (MIL) under SELF-DIAGNOSTIC SYSTEM.
Radiator Cooling Fan Relay
See appropriate ENGINE COOLING article in ENGINES.
FUEL DELIVERY
Fuel is sent under pressure from the fuel tank by the fuel pump, and the pressure is regulated by the fuel pressure regulator positioned downstream of the injectors.
Fuel Pump
Located within fuel tank, the fuel pump consists of an impeller driven by a DC motor. The pump has an internal check valve (to maintain system pressure) and a relief valve (to relieve excessive pressure).
Fuel Pressure Regulator
The fuel pressure regulator, located on the fuel delivery pipe, maintains a constant pressure at the injectors during all engine operating conditions.
This relay is located either at the left side of driver-side console or right side of passenger-side console. This multipurpose relay switches power to the MAF and VAF sensors, ISC motor, injectors, and fuel pump. For specific system configuration, see appropriate wiring diagram in WIRING DIAGRAMS.
Fuel is supplied to engine through electronically-pulsed (timed) fuel injectors. The ECM controls amount of fuel metered through injectors based on information received from various sensors.
The ISC actuator is a double-coil type. The 2 coils are driven by separate driver stages in the ECM. Depending on the pulse duty factor, the balance between the magnetic forces of the 2 coils will result in different angles of the motor. Actuator is located on by-pass hose to throttle body.
DIRECT IGNITION SYSTEM (DIS)
DIS is a molded, dual-coil system. System does not use a distributor. Ignition timing is controlled by the electronic control ignition timing system. The ignition timing curves for the engine operating conditions are programmed into the memory of the Engine Control Module (ECM).
The engine conditions (speed, load, warm-up condition, etc.) are detected by the various sensors. Based upon these sensor signals and the ignition timing curve data, signals to interrupt the primary current are sent, ignition coil is activated, and timing is controlled at the optimum point.
IGNITION TIMING CONTROL SYSTEM
The ECM controls ignition timing, based on signals from various engine sensors. Optimum ignition timing is controlled by making corrections for engine coolant temperature, intake air temperature, and other engine operating conditions.
Sonata 2.4L
ECM controls EGR operation by activating EGR control solenoid valve according to engine load. When engine is cold, ECM signals EGR control solenoid valve to deactivate EGR. ECM verifies EGR operation by monitoring the Manifold Absolute Pressure (MAP) sensor signal for a change in pressure when EGR is requested. EGR flow will result in a change in the MAP sensor signal. If signal does not change as expected, ECM will recognize this as an EGR malfunction, and will store a trouble code and turn on the Malfunction Indicator Light (MIL).
EVAPORATIVE & ORVR EMISSION (EVAP) CONTROL SYSTEM
EVAP and On-Board Refueling Vapor Recovery (ORVR) system consists of a fill vent valve, fuel shut-off valve, fuel cut (roll-over) valve, fuel liquid/vapor separator, EVAP canister, EVAP canister purge solenoid valve, EVAP canister close valve, vacuum relief filler cap, and connecting lines and hoses. ORVR system is designed to prevent the release of fuel vapors during refueling. During refueling, as fuel enters the fuel tank, a vacuum is created in filler pipe, drawing air into the filler pipe and tank. Fuel vapor in fuel tank is then forced to the EVAP canister via the fill vent valve and the fuel liquid/vapor separator. A fuel tank pressure sensor is used for detecting EVAP system leaks by comparing pressures inside and outside of fuel tank.
EVAP Canister Purge Solenoid Valve
Fuel vapors are vented into EVAP canister during refueling and when ignition is off. When engine is at normal operating temperature and engine speed is greater than idle, a thermovalve opens and allows vacuum to open the purge control valve. Canister vapors are then drawn into the intake manifold for burning during combustion. The purge control valve is kept closed during idle and engine warm-up to reduce HC and CO emissions.
POSITIVE CRANKCASE VENTILATION (PCV) VALVE
The positive crankcase ventilation system consists of a PCV valve and ventilation hoses. The PCV valve is located on the valve cover. When the engine is running, manifold vacuum pulls the PCV valve back, allowing crankcase fumes to enter intake manifold through a restricted orifice. As throttle opens, manifold vacuum drops, allowing PCV valve spring pressure to open PCV valve. This will increase volume of flow through valve to accommodate increase in crankcase blow-by gases. If the engine backfires through intake manifold, the PCV valve will be forced closed, preventing crankcase combustion.
The Malfunction Indicator Light (MIL) will illuminate for several seconds when the ignition is first turned on. Light remains illuminated for several seconds after engine has started. If an abnormal input signal from a sensor occurs, the MIL will illuminate and a DTC will be stored in ECM memory. For additional information, see appropriate SELF-DIAGNOSTICS article.
MISCELLANEOUS CONTROLS
Note. Although not considered true engine performance-related systems, controlled devices may affect driveability if they malfunction.
When A/C is turned on while engine is at idle, IAC actuator will increase engine idle speed. To prevent A/C compressor clutch from switching on before idle speed has increased, the ECM briefly opens the A/C relay circuit.