ENGINE CONTROL SYSTEM
Engine control system is a computerized emission, ignition and fuel injection control system. Engine control system lowers exhaust emissions while maintaining good fuel economy and driveability. Engine control system consists of various sensors, switches and control units. (Scheme 1)
An Engine Control Module (ECM) controls engine control system based on input signals received from various input devices. The ECM contains preprogrammed data to maintain optimum engine performance under all operating conditions.
Scheme 1
ENGINE CONTROL MODULE
The Engine Control Module (ECM) microcomputer receives input signals from various sensors, switches, and ignition and starting system components. The ECM uses this information for controlling various functions. See OUTPUT SIGNALS under COMPUTERIZED ENGINE CONTROLS.
The ECM has constant battery voltage at BATT terminal. The ECM contains a fail-safe function, used in case of sensor or switch failure. Fail-safe function uses preprogrammed values to provide a limp-in mode for minimal driveability. If a failure exists, ECM will inform the driver by turning on Malfunction Indicator Light (MIL) on the instrument panel.
Note. The MIL may also be referred to as the CHECK ENGINE light.
The ECM is equipped with a self-diagnostic function. Diagnostic trouble codes may be set by the malfunction of various engine sensors, switches or circuits, and stored in the ECM memory. When certain diagnostic trouble code is stored, Malfunction Indicator Light (MIL) on instrument panel may come on.
| Model | Location |
|---|---|
| RAV4 | Bottom Center Of Instrument Panel, In Front Of Console |
ECM LOCATION
Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the Engine Control Module (ECM). The second category covers OUTPUT SIGNALS , which are components controlled by the ECM.
INPUT DEVICES
Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input device usage on a specific model, see appropriate wiring diagram in WIRING DIAGRAMS article. The available input signals include the following
A/C Switch
When A/C is turned on, input signal is delivered to Engine Control Module (ECM). The ECM uses input signal to control engine idle speed during A/C operation.
Battery Signal
Battery voltage is always present at BATT terminal of Engine Control Module (ECM). When ignition is turned on, voltage for ECM operation is applied through EFI main relay to +B on ECM.
Camshaft & Crankshaft Position Sensors
Crankshaft position sensor and camshaft position sensor deliver input signals to Engine Control Module (ECM). Camshaft position sensor is a pick-up coil located in the distributor. Crankshaft position sensor is located at front (timing belt end) of engine, behind timing belt cover, near sprocket on crankshaft. The ECM may use input signals for controlling fuel injection system, ignition timing (spark advance) and idle speed control system.
Electrical Load Signal
An input signal is delivered to ELS terminal of Engine Control Module (ECM) to indicate when high electrical output is required. This signal is delivered when items such as rear window defroster, headlights, etc. are turned on. The ECM uses input signal to maintain proper idle speed.
Engine Coolant Temperature (ECT) Sensor
The ECT contains a built-in thermistor in which resistance varies according to engine coolant temperature. The ECT delivers an input signal to THW terminal of Engine Control Module (ECM). The ECM may use input signal for controlling fuel injection system, overdrive operation on electronically controlled transmissions/transaxles, ignition timing (spark advance), idle speed control system, fuel pressure control system (if equipped), heated oxygen sensor system (if equipped) and EGR system (if equipped).
Engine Cranking Signal
While engine is cranking and voltage is applied to the starter an input signal is also delivered to STA terminal of Engine Control Module (ECM). The ECM may use input signal for controlling fuel injection system, heated oxygen sensor system (if equipped), ignition timing (spark advance) and idle speed control system.
Intake Air Temperature Sensor
Intake air temperature sensor is mounted in air filter housing. Intake air temperature sensor measures incoming intake air temperature and delivers an input signal to THA terminal of Engine Control Module (ECM). The ECM may use input signal for controlling fuel injection system.
Knock Sensor
Knock sensor No. 1 monitors ignition knock conditions and delivers input signal to KNK terminal of Engine Control Module (ECM). The ECM may use input signal to determine ignition timing (spark advance) and control fuel injection system.
Manifold Absolute Pressure (MAP) Sensor
The MAP sensor monitors intake manifold intake air volume and delivers an input signal to Engine Control Module (ECM). The ECM may use input signal for controlling fuel injection system and ignition timing (spark advance).
Oxygen Sensor
Oxygen sensor monitors exhaust gas oxygen content and delivers an input signal to Engine Control Module (ECM). The ECM may use the input signal to determine ignition timing (spark advance) and control fuel injection system. Some models may be equipped with more than one oxygen sensor. On some models, a heated oxygen sensor may be used. On heated oxygen sensors, a heater is used to warm the oxygen sensor to improve oxygen sensor detection operation. The heater is controlled by the ECM.
Park/Neutral Position (PNP) Switch (A/T Models)
The PNP switch delivers an input signal to Engine Control Module (ECM), indicating gear position. The ECM may use input signal to control engine idle and fuel injection system.
Throttle Position (TP) Sensor
The TP sensor, mounted on throttle body, delivers an input signal indicating throttle position to the Engine Control Module (ECM). The ECM may use input signal for controlling fuel injection system, ignition timing (spark advance), idle speed control system, A/C-cut control system (if equipped), intake air control valve system (if equipped), EGR system (if equipped) and electronically controlled automatic transmissions/transaxles.
Note. Vapor pressure sensor may be referred to as EVAP vapor pressure sensor. Vapor pressure sensor VSV may be referred to as EVAP Vapor Pressure Sensor Vacuum Switching Valve (EVAP-VPSVSV).
Vapor Pressure Sensor
The Engine Control Module (ECM) monitors fuel tank pressure to determine if a leak or an abnormality exists in the EVAP system. A vapor pressure sensor Vacuum Switching Valve (VSV) is located in vapor line between fuel tank and charcoal canister. The ECM will operate the VSV, allowing vapor pressure sensor to monitor the fuel tank pressure. Vapor pressure sensor delivers an input signal to ECM to indicate fuel tank pressure.
Vehicle Speed Sensor
Vehicle speed sensor is mounted on transmission/transaxle. Vehicle speed sensor monitors vehicle speed and delivers an input signal to instrument cluster where the input signal is converted to a rectangular waveform and then sent to the Engine Control Module (ECM). The ECM determines vehicle speed by using input signal and may use input signal for controlling fuel injection system, idle speed control system and electronically controlled automatic transmission/transaxle (if equipped).
OUTPUT SIGNALS
Note. Vehicles are equipped with different combinations of computer-controlled components. Not all components listed below are used on every vehicle. For theory and operation on each output component, refer to system indicated after component.
The Engine Control Module (ECM) receives input from data sensors and switches, depending on model application, to control following components and sub-systems
A/C-Cut Control System
See IDLE SPEED under FUEL SYSTEM.
A/C Idle-Up System
See IDLE SPEED under FUEL SYSTEM.
Circuit Opening Relay
See FUEL DELIVERY under FUEL SYSTEM.
EGR Vacuum Switching Valve (VSV)
See EXHAUST GAS RECIRCULATION (EGR) SYSTEM under EMISSION SYSTEMS.
Electronically Controlled Transmission/Transaxle
See TRANSMISSION/TRANSAXLE CONTROLS under MISCELLANEOUS CONTROLS.
Electronic Spark Advance System
See DISTRIBUTOR TYPE IGNITION SYSTEM under IGNITION SYSTEM.
EVAP Vacuum Switching Valve (VSV)
See EVAPORATIVE EMISSION (EVAP) SYSTEM under EMISSION SYSTEMS.
Fuel Pressure Control System Vacuum Switching Valve (VSV)
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Pump
See FUEL DELIVERY under FUEL SYSTEM.
Idle Speed Control System
See IDLE SPEED under FUEL SYSTEM.
Self-Diagnostic System
See SELF-DIAGNOSTIC SYSTEM .
Vapor Pressure Sensor Vacuum Switching Valve (EVAP-VPSVSV)
See EVAPORATIVE EMISSION (EVAP) SYSTEM under EMISSION SYSTEMS.
FUEL DELIVERY
Vehicles are equipped with different combinations of fuel system electrical components. For complete wiring circuit of electrical components on a specific model, see appropriate wiring diagram in WIRING DIAGRAMS article.
Note. EFI main relay may also be referred to as EFI relay.
EFI Main Relay
The EFI fuse supplies constant battery voltage to EFI main relay. When ignition is turned on, voltage is supplied through IGN fuse to EFI main relay. EFI main relay is then energized and provides battery voltage to circuit opening relay, data link connector No. 1 and various other electrical components. The EFI main relay also provides battery voltage to +B terminal of Engine Control Module (ECM) when ignition is turned on. The EFI main relay is located in engine compartment relay box.
Circuit opening relay controls fuel pump circuit. When EFI main relay is energized, EFI main relay provides battery voltage to one side of circuit opening relay. When ignition is turned on, voltage is supplied to the other side of circuit opening relay. When proper input signals are delivered to the Engine Control Module (ECM), the circuit opening relay ground circuit is grounded at ECM terminal FC. Circuit opening relay then provides voltage to fuel pump for fuel pump operation. Circuit opening relay is located in relay box. See CIRCUIT OPENING RELAY LOCATIONS table.
| Application | Relay Location |
|---|---|
| RAV4 | Top Rear Relay In Relay Box Below Driver's Side Of Instrument Panel, Behind Kick Panel |
CIRCUIT OPENING RELAY LOCATIONS
Electric fuel pump is mounted in the fuel tank. Fuel pump operates at one specified speed.
Fuel Pressure Regulator
Fuel system is a returnless fuel system with fuel pressure regulator mounted on the fuel pump in the fuel tank. Fuel pressure regulator maintains constant fuel pressure to fuel injectors.
Fuel-Cut System
Controlled through input signals, the Engine Control Module (ECM) will shut off fuel delivery momentarily during closed throttle deceleration.
Fuel Injectors
Fuel injectors are electrically operated solenoids which deliver fuel to individual cylinders. The Engine Control Module (ECM) controls fuel injector duration based on various input signals to determine air/fuel mixture.
The Engine Control Module (ECM) uses various input signals for controlling the A/C-cut control system. The A/C-cut control system interrupts A/C compressor operation for a fixed period of time when vehicle accelerates from low engine speed.
Note. Idle speed control system may also be referred to as idle air control system.
Engine Control Module (ECM) is programmed with engine idle speed values. Idle speed control system provides a stable idle speed when engine is cold or idle speed decreases due to electrical load. The Engine Control Module (ECM) uses various input signals to maintain proper idle speed by controlling Idle Air Control (IAC) valve.
Throttle Opener
Throttle opener, mounted on throttle body, is vacuum controlled and allows engine to return to specified RPM after throttle is released.
DISTRIBUTOR TYPE IGNITION SYSTEM
Note. The distributor type ignition system may be referred to as Electronic Spark Advance (ESA) system.
Ignition system uses the Engine Control Module (ECM) for determining ignition timing (spark advance). ECM determines ignition timing (spark advance) based on various input signals. Following input signals may be used: engine coolant temperature, intake air temperature sensor, airflow meter, throttle position, engine RPM, vehicle speed sensor, A/C switch, brakelight signal, knock sensor, electrical load, MAP sensor and cranking (starter) signal. Input signals may vary depending on model application. Integrated (ignition coil on distributor) and remote ignition coil designs are used depending on model.
Crankshaft position and engine RPM input signals are delivered to Engine Control Module (ECM) by camshaft position sensor (pick-up coil) in the distributor and crankshaft position sensor. The ECM uses input signal for controlling ignition timing (spark advance). Crankshaft position sensor is located near crankshaft pulley. (Scheme 1)
Note. Camshaft position sensor in the distributor may be referred to as pick-up coils in distributor.
The ECM determines ignition timing and delivers an output ignition signal to the ignitor on the IGT wire. Since the width of the IGT signal is constant, the dwell angle control circuit in the ignitor determines the time the control circuit starts primary current flow to the ignition coil based on engine RPM and ignition timing one revolution ago.
When ignition timing in obtained, the primary circuit is turned off when ECM delivers a signal to ignitor on the IGT wire, causing ignition coil to fire the spark plug. After delivering a command to turn off primary circuit on the IGT wire, the ECM monitors IGF circuit to ignitor to ensure primary switching occurred. The ECM stops fuel injection as a fail-safe function when IGF reference signal has not been received.
EXHAUST GAS RECIRCULATION (EGR) SYSTEM
The EGR system reduces oxides of nitrogen (NOx) emissions by lowering combustion temperatures. Combustion temperatures are lowered by recycling metered amount of exhaust gases back into the intake system.
The EGR system contains a vacuum-operated EGR valve and a vacuum modulator. (Scheme 2) Vacuum modulator regulates exhaust backpressure and balances atmospheric pressure and vacuum to allow EGR operation at heavy throttle.
A check valve, EGR cooler, EGR Vacuum Switching Valve (VSV) and EGR gas temperature sensor may also be used depending on vehicle application.
The EGR cooler, used on some models, assists in reducing exhaust gas temperature before entering combustion chamber. The EGR operation is controlled by a EGR Vacuum Switching Valve (VSV) which is controlled by the Engine Control Module (ECM).
The ECM may use various input signals such as engine coolant temperature, engine RPM, throttle position, airflow meter and vehicle speed for controlling the EGR VSV. Various model and engine types have different EGR system components. For EGR system and component testing, see EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM/COMPONENT TESTS article.
Scheme 2
EVAPORATIVE EMISSION (EVAP) SYSTEM
Note. The EVAP may also be referred to as fuel evaporation.
The EVAP system prevents fuel tank gasoline vapors from escaping into the atmosphere. Fuel tank gasoline vapors are routed through charcoal canister into intake manifold for combustion in the cylinders. (Scheme 3)
The Engine Control Module (ECM) monitors fuel tank pressure to determine if a leak or an abnormality exists in the EVAP system. A vapor pressure sensor Vacuum Switching Valve (VSV) is located in vapor line between fuel tank and EVAP canister. The ECM will operate the VSV, allowing vapor pressure sensor to monitor the fuel tank pressure. Vapor pressure sensor delivers an input signal to ECM to indicate fuel tank pressure. If a leak or an abnormality exists in the EVAP system, a diagnostic trouble code will be stored in the Engine Control Module (ECM).
An EVAP Vacuum Switching Valve (VSV) is used to control EVAP system. The Engine Control Module (ECM) controls EVAP VSV which controls the vacuum flow for EVAP operation.
For EVAP system and component testing, see FUEL EVAPORATION under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM/COMPONENT TESTS article.
Scheme 3
POSITIVE CRANKCASE VENTILATION
The Positive Crankcase Ventilation (PCV) system prevents crankcase hydrocarbon (HC) vapors from escaping into the atmosphere. Crankcase vapors are routed from crankcase through a vacuum-controlled PCV valve and then delivered back into the cylinders. (Scheme 4)
The PCV system provides primary control of crankcase blow-by vapors, according to manifold vacuum. When manifold vacuum is high (at idle), PCV restricts vapor flow to maintain a smooth idle condition.
Scheme 4
TRANSMISSION/TRANSAXLE CONTROLS
Note. Only electronically controlled transmissions/transaxles are covered. Some models have transmissions and transaxles that are not electronically controlled.
Electronically Controlled Transmission/Transaxle (ECT)
The Engine Control Module (ECM) uses input signals for controlling transmission/transaxle operation.