AIR INDUCTION SYSTEM
All models use a Volume Airflow (VAF) sensor. The air induction system uses. A remote air filter is connected to a plenum-mounted throttle body.
INTAKE MANIFOLD TUNING SYSTEM
When engine is operating in low-to-medium speed range (approximately 4,000 RPM maximum), Powertrain Control Module (PCM) turns ON power transistor in order to turn ON intake manifold tuning solenoid. (Scheme 1) Consequently, intake manifold vacuum that is stored in vacuum tank acts on vacuum control actuator, thus causing control valve at secondary port of each cylinder to fully close. Even if intake manifold vacuum decreases during a high-load operation, vacuum from vacuum tank maintains control valve fully closed.
When engine is operating in high-speed range (approximately 4,000 RPM minimum), PCM turns OFF power transistor in order to turn OFF intake manifold tuning solenoid. Consequently, intake manifold tuning solenoid introduces atmospheric pressure to vacuum control actuator, thus causing control valves of secondary ports to fully open.
Scheme 1
COMPUTERIZED ENGINE CONTROLS
The computerized engine control system controls fuel injection, ignition timing, idle speed and emission control systems.
ENGINE CONTROL MODULE/POWERTRAIN CONTROL MODULE
Note. For purpose of simplification, ECM and PCM will be refired to as PCM.
Vehicles equipped with manual transmission use an Engine Control Module (ECM). Vehicles equipped with automatic transmission use either ECM with separate Transmission Control Module (TCM), or a Powertrain Control Module (PCM), depending on model. PCM combines functions of ECM and TCM. PCM receives and processes signals from input devices. Operating conditions such as cold starting, altitude changes, acceleration and deceleration affect input device signals. Based on signals received, PCM sends signals to various components which control fuel injection, ignition timing, idle speed and emission control systems. For PCM location (Scheme 2)- (Scheme 15).
Scheme 2
Scheme 3
Scheme 4
Scheme 5
Scheme 6
Scheme 7
Scheme 8
Scheme 9
Scheme 10
Scheme 11
Scheme 12
Scheme 13
Scheme 14
Scheme 15
Note. Components are grouped into 2 categories. First category covers INPUT DEVICES , which control or produce voltage signals monitored by PCM. Second category covers OUTPUT SIGNALS , which are components controlled by PCM.
ELECTRONIC THROTTLE CONTROL SYSTEM (MONTERO)
An electronically controlled throttle valve system, which electronically regulates throttle valve opening, is used. Engine control unit in Powertrain Control Module (PCM) monitors amount of accelerator pedal travel through accelerator pedal position sensor and issues premapped target throttle valve opening values to throttle actuator control unit in PCM in accordance with operating conditions. (Scheme 16) Thus, throttle actuator control unit achieves target throttle valve opening by controlling current supplied to throttle actuator motor, which is attached to throttle body.
This system also controls idle speed in addition to controlling throttle valve opening. Thus, previously used Idle Air Control (IAC) motor has been discontinued.
This system can also effect auto-cruise control as an extension of throttle valve opening control. Therefore, an auto-cruise control function has been integrated in PCM.
The operation of throttle valve is controlled to target throttle opening, which is determined by amount of accelerator pedal travel and driving conditions.
The PCM continuously calculates actual idle speed in order to effect idle speed control. If there is a difference from target idle speed, two types of controls are effected: engine speed feedback control that actuates throttle valve in order to correct actual idle speed to target idle speed; and throttle position control that actuates throttle valve in order to accommodate load fluctuations that are caused by A/C or other loads.
The engine speed feedback control regulates volume of air that flows through throttle valve by actuating throttle valve, in order to maintain engine at a prescribed target idle speed. An optimal target idle speed is set to suit every operating condition (such as whether A/C switch is ON or OFF). Engine speed feedback control is effected only when prescribed operating conditions are met, and throttle valve position control is effected at all other times.
While engine is operating at idle, idle speed could change suddenly when load that is applied to engine changes, such as when steering wheel is turned, air conditioning switch is turned ON/OFF, or shift lever is operated. Immediately after any of these signals are detected, this control actuates throttle valve until target position is attained, in order to regulate volume of air that flows through throttle valve. Thus, fluctuation of engine speed is restrained.
If engine control unit or throttle actuator control unit in PCM detects a malfunction in system, it illuminates Malfunction indicator lamp (SERVICE ENGINE SOON or check engine lamp). At same time, PCM reduces engine output by restricting throttle valve opening or by cutting off fuel supply, or, it disables throttle actuator control motor by cutting off power to throttle actuator control motor relay. When power to throttle actuator control motor relay is cut off, throttle valve assumes a prescribed opening (to supply a volume of air that enables a minimum operation of vehicle). Thus, this control enables vehicle to be driven at a minimum level even if a malfunction occurs in throttle control system.
Scheme 16
Throttle Actuator Control Motor
The throttle actuator control motor is built into throttle body and opens and closes throttle valve via deceleration gears. (Scheme 18) PCM switches direction of electricity in accordance with open/close direction, as well as modulating electrical current to motor coil by controlling Pulse Wide Modulation (PWM) and controlling throttle actuator control motor.
The throttle actuator control motor is a DC motor fitted with small brushes that has excellent responsiveness and electrical consumption capabilities, and which enables acquisition of rotary power that is proportional to electrical current volume imprinted on coil. (Scheme 17) In addition to this, motor's rotors consist of seven poles and seven circuits so that throttle valve can still be driven with other poles in event of one circuit being cut off. Throttle valve has been designed so that it is open a predetermined amount when no electricity is passing through to throttle actuator control motor in order to ensure that a minimal amount of movement is still possible when a system failure cuts off power.
Scheme 17
INPUT DEVICES
Note. Vehicles are equipped with different combinations of input devices. Not all input devices are used on all models. To determine input device usage on specific models, see ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. The following are available input devices
Accelerator Pedal Position Sensor (Montero)
The accelerator pedal position sensor detects amount of travel of accelerator pedal. Mounted on accelerator pedal arm, this sensor outputs a voltage signal, which corresponds to amount of pedal travel, to Powertrain Control Module (PCM). Through this signal, PCM determines target opening of throttle valve.
Similar to conventional Throttle Position (TP) sensor, accelerator pedal position sensor is a variable resistor that outputs a voltage in proportion to amount of travel (opening) of accelerator pedal. Accelerator pedal position sensor uses two systems (main and sub) for power, ground, and output signals. This improves accuracy of system to detect malfunctions and reinforces fail-safe function in order to ensure reliability.
Accelerator Pedal Position Switch (Montero)
The accelerator pedal position switch consists of a contact point type switch, which is located in accelerator pedal position sensor. Contact points open when amount of travel of accelerator pedal exceeds a prescribed value. Powertrain control module uses this signal for detecting any malfunctions in characteristics of accelerator pedal position sensor.
A/C Switch
When A/C is turned on, signal is sent to PCM. With engine at idle, PCM increases idle speed through Idle Air Control (IAC) motor.
A/C Pressure Sensor (Eclipse 2.4L & Outlander)
The A/C pressure sensor detects A/C refrigerant pressure to input actuation (low load or high load) condition of A/C compressor into PCM. Based on this input signal, PCM controls A/C idle-up speed.
Barometric Pressure Sensor
Barometric (BARO) sensor is incorporated into Volume Air Flow (VAF) sensor assembly. BARO sensor converts barometric pressure to an electrical signal, which is sent to PCM. PCM adjusts air/fuel ratio and ignition timing according to changes in altitude.
Camshaft Position Sensor
Camshaft Position (CMP) sensor is a Hall-Effect type sensor. PCM determines cylinder No. 1 TDC based on pulse signals received from CMP sensor. CMP sensor input is used to determine injector triggering sequence. On vehicles with Distributorless Ignition Systems (DIS) CMP sensor input is also used to determine which ignition coil to fire. On engines with distributor, CMP sensor is located in distributor. On engines with DIS, CMP sensor is located at front or rear of engine by camshaft.
Closed Throttle Position Switch (Diamante)
Closed throttle position switch is located inside Throttle Position (TP) sensor. PCM senses whether accelerator pedal is depressed or not. High voltage (open) or low voltage (closed) signal is input to PCM, which then controls Idle Air Control (IAC) motor based on input signal.
Crankshaft Position Sensor
Crankshaft Position (CKP) sensor is located on front of engine by crankshaft. PCM determines crankshaft position based on pulse signals received from CKP sensor. CKP sensors input is used to determine injector timing and ignition timing.
Engine Coolant Temperature Sensor
Engine Coolant Temperature (ECT) sensor converts coolant temperature to electrical signal for use by PCM. ECT input is used for fuel injection pulse width modulation, idle air control and ignition timing control by PCM. PCM can not go into closed loop fuel system management until ECT input indicates engine is at normal operating temperature.
Fuel Tank Differential Pressure Sensor
A voltage proportional to pressure in fuel tank is sent from output terminal of fuel tank differential sensor to PCM. PCM monitors performance of Evaporative Emission Control System (EVAP) system using these signals. It also uses input from Fuel Tank Differential Pressure (FTDP) sensor to monitor EVAP system pressure changes and calculates whether leak exists.
Fuel Level Sensor
The fuel gauge drive signal is input to PCM. PCM monitors this sensor in case of open or short circuit malfunction.
Fuel Temperature Sensor (Except Diamante)
The fuel temperature sensor converts fuel temperature to a voltage. PCM detects fuel temperature in fuel tank with this voltage. PCM monitors this sensor in case of open or short circuit malfunction.
Heated Oxygen Sensor
Heated Oxygen Sensor (HO2S) detects oxygen content in exhaust gas and sends this information to PCM. PCM uses input signals from front HO2S to control air-fuel mixture by varying duration of fuel injection. PCM compares signals from rear HO2S to signals from front HO2S to monitor catalytic converter performance. HO2S heater speeds heating of HO2S which speeds up entry into closed loop operation. HO2S heater also stabilizes sensor temperature regardless of exhaust gas temperature to allow for more accurate exhaust oxygen content readings.
Intake Air Temperature Sensor
Intake Air Temperature (IAT) sensor is incorporated into Volume Air Flow (VAF) sensor assembly. This resistor-based sensor measures temperature of incoming air and sends an analog signal to PCM. Depending on configuration, IAT input may be used for fuel injection, idle air, and/or ignition timing control.
Knock Sensor
Knock Sensor (KS) is located in cylinder block and senses engine vibration during detonation (knock). KS converts vibration into electrical signal. PCM retards ignition timing based on this signal.
Manifold Differential Pressure Sensor
Manifold Differential Pressure (MDP) sensor converts negative air pressure in intake manifold plenum into voltage signals sent to PCM. PCM monitors performance of Exhaust Gas Recirculation (EGR) system using these signals.
Output Shaft Speed Sensor (A/T)
Mounted on transmission, output shaft speed sensor sends a pulsing signal to PCM for vehicle speed calculation. PCM uses this calculation for cruise control and fuel cut-off.
Park/Neutral Position Switch (Automatic Transmission)
Park/Neutral Position (PNP) switch senses position of transmission select lever, indicating engine load due to automatic transmission engagement. Based on this signal, PCM commands IAC motor to maintain optimum idle speed.
Power Steering Oil Pressure Switch
Switch detects increase in power steering oil pressure. When power steering oil pressure increases, switch contacts close, signaling PCM. PCM commands IAC motor, to maintain optimum idle speed.
Throttle Position Sensor (Except Montero)
Throttle Position (TP) sensor is a variable resistor mounted on throttle body. PCM uses voltage signal from TP sensor to determine throttle plate angle. TP sensor input is used for fuel injection control and idle air control.
Throttle Position Sensor (Montero)
The Throttle Position (TP) sensor, which is located in throttle body, outputs a voltage signal, which corresponds to rotational angle of throttle shaft, to Powertrain Control Module (PCM). (Scheme 18) In accordance with this signal, PCM effects feedback control of throttle actuator control motor. This TP sensor uses a non-contact Hall IC to enhance its reliability.
The TP sensor consists of a permanent magnet fixed to throttle shaft, a Hall IC that outputs electrical voltage in accordance with magnetic flux density, and a stator that effectively guides magnetic flux from permanent magnet into Hall IC. (Scheme 19)
The magnetic flux density that passes into Hall IC when throttle valve is fully closed is kept to a minimum, resulting in minimal electrical voltage output. (Scheme 20) Magnetic flux density that passes into Hall IC when throttle valve is fully open is kept to a maximum, resulting in maximal electrical voltage output.
The TP sensor outputs through two systems (main and sub). This improves accuracy of system to detect malfunctions and reinforces fail-safe function in order to ensure reliability.
Scheme 18
Scheme 19
Scheme 20
Vehicle Speed Sensor (M/T)
Mounted on transmission, Vehicle Speed Sensor (VSS) sends a pulsing signal to PCM for vehicle speed calculation. PCM uses this calculation for cruise control and fuel cut-off.
Volume Airflow Sensor
Volume Airflow (VAF) sensor is located in air intake system behind air cleaner. VAF sensor is a vortex type sensor that sends frequency signal to PCM. PCM uses signal to calculate intake air flow rate and adjust air/fuel ratio by controlling fuel injector duration.
OUTPUT SIGNALS
Note. Vehicles are equipped with various combinations of computer-controlled components. Not all components listed below are used on every vehicle. To determine component usage on specific models, see ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. For theory and operation on each output component, refer to system indicated after component.
A/C Compressor Clutch Relay Control
See A/C RELAY under IDLE SPEED under FUEL SYSTEM.
Data Link Connector
See SELF-DIAGNOSTIC SYSTEM .
EGR Solenoid (Except Montero)
See EXHAUST GAS RECIRCULATION CONTROL (EXCEPT MONTERO) under EMISSION SYSTEMS.
EGR Valve Stepper Motor (Montero)
See EXHAUST GAS RECIRCULATION CONTROL (MONTERO) under EMISSION SYSTEMS.
Fuel Injectors
See FUEL INJECTORS under FUEL CONTROL under FUEL SYSTEM.
Fuel Pump Relay Control
See FUEL PUMP RELAY CONTROL under FUEL DELIVERY under FUEL SYSTEM.
Idle Air Control Motor
See IDLE AIR CONTROL MOTOR under IDLE SPEED under FUEL SYSTEM.
Intake Manifold Tuning Solenoid/Variable Induction Control Solenoid (Eclipse 3.0L & Montero)
See INTAKE MANIFOLD TUNING SYSTEM under AIR INDUCTION SYSTEM.
Malfunction Indicator Light
See MALFUNCTION INDICATOR LIGHT under SELF-DIAGNOSTIC SYSTEM.
Power Transistor(s) & Ignition Coils (Except Galant 3.0L & Eclipse 3.0L)
See IGNITION SYSTEMS .
Purge Solenoid Valve
See PURGE SOLENOID VALVE under EVAPORATIVE EMISSION CONTROL under EMISSION SYSTEMS.
See THROTTLE ACTUATOR CONTROL MOTOR under IDLE SPEED in FUEL SYSTEM.
Vent Solenoid Valve
See VENT SOLENOID VALVE under EVAPORATIVE EMISSION CONTROL under EMISSION SYSTEMS.
FUEL DELIVERY
Electric fuel pump, located in gas tank, feeds fuel through in-tank fuel filter, external fuel filter (located in engine compartment) and fuel injector rail.
Fuel Pump
Fuel pump consists of a motor-driven impeller. Pump has an internal check valve to maintain system pressure, and a relief valve to protect fuel pressure circuit. Pump receives voltage supply from MFI control relay.
PCM turns fuel pump relay ON, via MFI control relay, so that current is supplied to fuel pump while engine is cranking or running.
Fuel Pressure Regulator
Located on fuel injector rail, this diaphragm-operated valve adjusts fuel pressure according to engine manifold vacuum.
As engine manifold vacuum increases (closed throttle), fuel pressure regulator diaphragm opens valve, allowing pressure to bleed off through fuel return line, reducing fuel pressure.
As engine manifold vacuum decreases (open throttle), fuel pressure regulator diaphragm closes valve, preventing pressure from bleeding off through fuel return line, increasing fuel pressure.
Fuel is supplied to engine through sequentially electronically pulsed (timed) injectors located on fuel rail(s). PCM controls amount of fuel metered through injectors (injector on-time) based on information received from sensors.
A/C Relay
When A/C is turned on with engine at idle, PCM signals IAC motor to increase idle speed. To prevent A/C compressor from switching on before idle speed has increased, PCM momentarily opens A/C relay circuit.
Stepper motor controls pintle-type air valve to regulate volume of intake air at idle.
During start mode, PCM controls idle intake air volume according to Engine Coolant Temperature (ECT) sensor input. After starting, with when throttle is in idle position, idle speed is controlled by Idle Air Control (IAC) motor.
When throttle is opened, IAC motor moves to a preset position in accordance with ECT sensor input.
PCM signals IAC motor to increase engine RPM in following situations: A/T (if applicable) is shifted from Neutral to Drive, A/C is turned on, or power steering pressure reaches a preset value.
On Outlander, idle air control is basically same as that for 2.4L engine installed on Eclipse. However, system has been simplified by discontinuing use of air volume limiter.
DISTRIBUTORLESS IGNITION SYSTEM
Depending on number of cylinders, ignition system is a 2-coil or 3-coil, distributorless ignition system. PCM controls timing and directly activates each power transistor to fire coils. On 4-cylinder engines, power transistor "A" controls primary current of ignition coil "A" to fire spark plugs on cylinders No. 1 and 4 at same time. Power transistor "B" controls primary current of ignition coil "B" to fire spark plugs on cylinders No. 2 and No. 3 at same time. On V6 engines, companion cylinders No. 1 and 4, 2 and 5, and 3 and 6 are fired together.
PCM uses signals from CMP sensor to determine which coil to fire. PCM uses signals from CKP sensor to adjust timing. Additional inputs from VAF sensor, IAT sensor, BARO sensor, ECT sensor, closed Throttle Position (TP) sensor, ignition switch, PNP switch (automatic transmissions), Knock Sensor (KS) and VSS are used by PCM to optimize timing for operating conditions. When engine is cold or operated at high altitudes, PCM will advance timing.
Eclipse 2.4L, Galant 2.4L, Lancer & Outlander
Distributorless Ignition System (DIS) consists of 2 ignition coils with built-in ignition power transistors, ignition failure sensor, Camshaft Position (CMP) sensor, Crankshaft Position (CKP) sensor, and PCM. CMP sensor is located by camshaft. CKP sensor is located on front of engine near crankshaft.
Montero & Montero Sport
Distributorless Ignition System (DIS) consists of 3 ignition coils, ignition power transistor unit containing 3 transistors, Camshaft Position (CMP) sensor, Crankshaft Position (CKP) sensor and PCM. CMP sensor is located on front of engine by camshaft. CKP sensor is located on front of engine near crankshaft.
HALL EFFECT IGNITION SYSTEM
System is equipped with a Hall Effect distributor. Shutter(s) attached to distributor shaft rotate through distributor Hall Effect switch, also referred to as a Camshaft Position (CMP) sensor, which contains a distributor pick-up (a Hall Effect device and magnet). As shutter blade(s) pass through pick-up, magnetic field is interrupted and voltage is toggled between high and low. PCM uses this data along with Crankshaft Position (CKP) sensor data to control ignition timing and injector pulse width. Additional inputs from VAF sensor, IAT sensor, BARO sensor, ECT sensor, closed Throttle Position (TP) sensor, ignition switch, PNP switch (automatic transmission), and VSS are used by PCM to optimize timing for operating conditions.
Diamante, Eclipse 3.0L & Galant 3.0L
Ignition system consists of distributor assembly, Camshaft Position (CMP) sensor, Crankshaft Position (CKP) sensor, ignition coil, ignition power transistor, knock sensor (if applicable) and PCM. Hall effect type CMP sensor, coil and ignition power transistor are located in distributor assembly. When automatic transmission shifts gears, ignition timing is retarded. When engine is cold or operated at high altitude, PCM will slightly advance timing. If engine has knock sensor and engine is knocking, PCM will retard timing.
IGNITION TIMING CONTROL SYSTEM
Ignition timing is controlled by PCM. PCM adjusts timing based on various conditions such as engine temperature, altitude and detonation. Ignition timing is checked using a scan tool and is not adjustable.
EXHAUST GAS RECIRCULATION CONTROL (EXCEPT MONTERO)
System consists of Exhaust Gas Recirculation (EGR) valve, EGR solenoid, vacuum control valve, hoses and PCM. EGR valve is opened by manifold vacuum passing through vacuum control valve. EGR solenoid works as a vacuum bleed between vacuum control valve and EGR valve. When EGR solenoid is off, vacuum is bled off so not enough vacuum exists at EGR valve to open EGR valve. When EGR solenoid is on, vacuum bleed is closed so that vacuum from vacuum control valve is applied to EGR valve.
When engine is cold, PCM signals EGR control solenoid valve to deactivate EGR system. When engine is warmed up, PCM will control EGR system operation according to engine operating conditions. OBD-II monitors EGR system via Manifold Differential Pressure (MDP) sensor.
EXHAUST GAS RECIRCULATION CONTROL (MONTERO)
Through adoption of a stepper motor, this Exhaust Gas Recirculation (EGR) valve is able to control EGR flow rate in a highly accurate manner, thus reducing exhaust gas (NOx) emissions and improving fuel economy.
In EGR valve, stepper motor rotor rotates clockwise or counterclockwise in accordance with signals from Powertrain Control Module (PCM). This causes shaft, which is joined to rotor with screw threads, to extend or contract. (Scheme 21) Movement of shaft causes valve to move vertically, in order to control clearance of EGR passage.
The stepper motor, which rotates 15° per step, rotates clockwise or counterclockwise only in angle that corresponds to number of pulse signals (steps) that are output by PCM. Thus, EGR flow rate is regulated in accordance with number of pulse signals (steps) that are output by PCM. PCM rotates stepper motor rotor by sequentially switching phases of four coils in stepper motor in accordance with ON/OFF patterns.
When ignition switch is ON position, this system actuates stepper motor to fully close for positioning (initialization) purposes.
Scheme 21
EVAPORATIVE EMISSION CONTROL
Fuel Evaporation Emission Control (EVAP) system prevents fuel vapor from entering atmosphere. EVAP system consists of fuel tank, fuel overflow limiter valve (fuel vent valve), fuel cutoff valve, EVAP canister, purge solenoid valve, vent solenoid valve, Fuel Tank Differential Pressure (FTDP) sensor and connecting lines and hoses. EVAP system in some models may also include vent valve, leveling valve and/or liquid separator.
Fuel vapors from fuel tank are stored temporarily in EVAP canister until drawn into engine through intake manifold and burned. When PCM turns purge solenoid on, vapors are drawn from EVAP canister into intake manifold. When engine coolant temperature is low, or when intake air volume is low (idle), PCM turns solenoid off.
OBD-II system runs tests (monitors) on EVAP system to check for leaks. During EVAP system monitor, PCM seals EVAP system by closing purge solenoid valve and vent solenoid valve. Once EVAP system is closed, PCM uses input from FTDP sensor to monitor EVAP system pressure changes and calculates whether leak exists. If EVAP system leak is detected, MIL will illuminate and a DTC will set.
Purge solenoid valve is normally closed. When engine is off, fuel vapors are vented into EVAP canister. When engine is warmed to normal operating temperature and running at speeds greater than idle, PCM energizes purge solenoid valve, allowing vacuum to purge canister.
Canister vapors are then drawn through purge solenoid valve into intake manifold for burning. Purge solenoid valve remains closed during idle and engine warm-up to reduce HC (hydrocarbons) and CO (carbon monoxide) emissions. PCM also controls purge solenoid valve to test EVAP system for leaks.
Vent solenoid valve is located between canister and atmosphere. It is used by OBD-II to test EVAP system for leaks. Normally vent solenoid valve is off so that canister is vented to atmosphere. When monitoring for leaks, PCM commands vent solenoid valve on which closes EVAP canister atmospheric vent.
Fuel Overflow Limiter Valve
Fuel overflow limiter valve is located in fuel filler neck. It prevents overfilling of fuel tank.
Fuel Cutoff Valve
Fuel cutoff valve prevents fuel leaks if vehicle is rolled over in a accident.
POSITIVE CRANKCASE VENTILATION VALVE
Positive Crankcase Ventilation (PCV) valve operates in closed crankcase ventilation system. Closed crankcase ventilation system consists of PCV valve and ventilation hoses.
PCV valve is a one-way check valve located in valve cover. PCV valve plunger position is regulated by intake manifold vacuum which regulates flow of blow-by gasses. Blow-by gas flow is lessened when engine is under low load to maintain engine stability. Blow-by is increased when engine is under high load to improve crankcase ventilation. If engine backfires through intake manifold, PCV valve closes to prevent crankcase combustion.
On OBD-II systems, MIL (CHECK ENGINE light) will illuminate only for emissions system related faults or deterioration. Malfunction Indicator Light (MIL) comes on when ignition is turned on. MIL remains on for 5 seconds after engine has started, then will go out if no DTCs are stored in PCM memory. If an emission systems related fault occurs according to preset criteria, a DTC will set and MIL will illuminate. Any fault must be repaired and DTC cleared. If PCM determines that system has returned to normal, MIL will be turned off by PCM.