INTRODUCTION
This article covers basic description and operation of engine performance-related systems and components. Read this article before diagnosing vehicles or systems with which you are not completely familiar.
AIR INDUCTION SYSTEM
Main components of air intake system are air cleaner, Mass Air Flow (MAF) sensor, air cleaner outlet hose, throttle body (with fast idle control system), Idle Air Control (IAC) valve and intake manifold.
Air (by amount corresponding to throttle valve opening and engine speed) is filtered by air cleaner, passes to throttle body, is distributed by intake manifold and finally drawn into each combustion chamber. When IAC valve is opened according to signal from ECM, air bypasses throttle valve through bypass passage and finally drawn into intake manifold.
When engine is cold, fast idle control system increases engine speed by opening throttle valve to send air to intake manifold, and thus engine warm up. To identify air intake system and fast idle control (Scheme 1), (Scheme 2) or (Scheme 3).
Scheme 1
Scheme 2
Scheme 3
COMPUTERIZED ENGINE CONTROLS
Note. Some states have adopted California emission standards. Refer to underhood vehicle emissions control information label for specific emission specifications and adjustment procedures.
All engines use Sequential Multiport Fuel Injection (SFI) and Distributorless Ignition System (DIS) controlled by Engine Control Module (ECM). Input devices supply ECM with signals which indicate operating conditions of the vehicle. ECM output signals control systems which control vehicle operation to optimize emission control and vehicle performance.
ENGINE CONTROL MODULE
Note. See PIN VOLTAGE/CIRCUIT RESISTANCE CHARTS article and ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS in ELECTRICAL for ECM connector and wire terminal identification.
Engine Control Module (ECM) monitors system inputs and controls system outputs accordingly to obtain optimal fuel economy and engine performance, while maintaining acceptable exhaust emission levels. In event of an input or output failure, ECM will memorize and store information as a Diagnostic Trouble Code (DTC). DTCs can be used by technician to diagnose various driveability and emission related problems. DTCs are accessed through On-Board Diagnostics II (OBD II) Data Link Connector (DLC) with use of a Suzuki scan tool or other OBD II compatible scan tool. DLC is located under instrument panel, accessible from driver's side. (Scheme 4)
ECM incorporates a fail-safe (limp-in) mode. If a fault occurs during vehicle operation, ECM will substitute a predetermined value and/or signal for continued operation. Driving performance will be affected, but vehicle may still be driven. When ECM detects a system fault, Malfunction Indicator Light (MIL) will flash or illuminate steadily to notify driver of a developing problem.
Scheme 4
ECM Voltage Supply
See ENGINE CONTROL MODULE POWER & GROUND CIRCUIT CHECK/ENGINE DOES NOT START under SYSTEM TESTS in appropriate SELF DIAGNOSTICS article.
On-Board Diagnostic System Description
Engine Control Module (ECM) has the following function in compliance with OBD-II regulations
- When ignition switch is turned to ON position with engine not running, Malfunction Indicator Light (MIL) turns ON to check of MIL bulb.
- When ECM detects a malfunction which gives an adverse effect to vehicle emission while engine is running, it makes MIL in instrument cluster turn ON or flash (flashing only when detecting a misfire which can damage to catalyst) and store malfunction Diagnostic Trouble Code (DTC) related to affected area in its memory (DTC according to SEA J2012).
- As a condition for detecting a malfunction in some areas in system being monitored by ECM and turning ON MIL due to that malfunction, 2 driving cycles detection logic is adopted to prevent erroneous detection.
- When a malfunction is detected, engine and driving conditions then are stored in ECM memory as freeze frame data. See «FREEZE FRAME DATA»(/suzuki/grand-vitara/i-2000-2006/remont/theory-operation/#engine-controls-theory-operation__freeze-frame-data) .
- It is possible to communicate via Data Link Connector (DLC) by using Suzuki scan tool. Also OBD-II generic scan tool which are in compliance with SEA J1978 (Diagnostic information can be accessed by using a scan tool).
Warm-Up Cycle
A warm-up cycle means sufficient vehicle operation such that coolant temperature has risen by a least 40 °F (22 °C) from engine starting and reaches a minimum temperature of 160 °F (70 C).
Driving Cycle
A drive cycle consist s of two parts, engine start-up and engine shutoff.
2 Driving Cycle Detection Logic
Malfunction detected in first driving cycle is stored in ECM memory (in form of pending DTC) but MIL does not illuminate at this time. MIL illuminates when detection of same malfunction is detected in next drive cycle.
Pending DTC
Pending DTC means a DTC detected and stored temporarily at one drive cycle of DTC which is detected in two driving cycle detection logic.
Freeze Frame Data
ECM stores engine and driving conditions at moment of detection of a malfunction in its memory. This data is called "Freeze Frame Data".
Therefore it is possible to know engine and driving conditions (e.g. whether engine is warm or not, where vehicle was running or stopped, where air/fuel mixture was lean or rich) when a malfunction was detected by checking freeze frame data. Also, ECM has a function to store each freeze frame data for three different malfunctions in order as malfunction is detected. Utilizing this function, it is possible to know order of malfunction that have been detected. Its use is helpful when rechecking or diagnosing a trouble.
INPUT DEVICES
Note. Components are grouped into 2 categories. First category is INPUT DEVICES , which are components that control or produce voltage signals monitored by ECM. Second category is OUTPUT SIGNALS , which are components controlled by ECM.
A/C Signal
See MISCELLANEOUS CONTROLS .
Camshaft Position Sensor
Camshaft Position (CMP) sensor is Hall Effect-type mounted to rear of engine, beside camshaft. As camshaft turns, signal rotor interrupts magnetic field, generating a high/low AC signal (2 per revolution). ECM uses this signal to determine which cylinder is in compression stroke.
Crankshaft Position Sensor
Crankshaft Position (CKP) sensor is mounted on bottom front side of oil pan. CKP sensor consists of a pick-up coil and magnet. CKP sensor generates an AC voltage signal as signal rotor on crankshaft timing belt pulley rotates. This signal is sent to ECM and is used to monitor misfire conditions, calculate engine speed and cylinder identification.
Electric Load Signal
This signal is sent to ECM from headlights, clearance lights, heater fan, stop lights or rear window defogger as one or more accessory is turned on. ECM uses this signal to control operation of idle control system to compensate for electrical load on engine.
Engine Coolant Temperature Sensor
Engine Coolant Temperature (ECT) sensor is a thermistor which changes resistance with respect to coolant temperature. High temperature causes low resistance. Low temperature causes high resistance. A reference voltage (supplied and monitored by ECM) is modified by sensor resistance. ECM uses this information to control operation of various devices.
Engine Start Signal
This signal is sent from starter circuit to ECM as engine is cranked. ECM uses this signal to monitor when engine is cranking to activate fuel pump relay and fuel injector(s).
Fail-Safe Function
When a malfunction has occurred in engine and emission control system, a failure signal is sent to ECM. Control over injection, IAC actuator and others is maintained on basis of standard signals and/or back-up program stored in the ECM. When in fail-safe mode failure signal and/or CPU input is ignored. When in this function, a certain level of engine performance is available even when failure occurs and disability in running is avoided.
Fuel Level Signal
Fuel level signal is sent from the fuel level sensor installed in fuel tank. ECM uses this signal to monitor conditions for detecting malfunctions.
Fuel Tank Pressure Sensor
Fuel Tank Pressure (FTP) sensor receives a 5-volt reference from ECM. As fuel tank pressure changes, resistance of sensor changes and sends a voltage signal back to ECM. This signal is used by ECM to determine if a leak exists in EVAP system.
Heated Oxygen Sensor No. 1
Heated Oxygen Sensor (HO2S) No. 1 is mounted in exhaust manifold in front of catalytic converter. HO2S No. 1 produces 0.1-0.9 volt when exhaust system temperatures are greater than 600 °F (316 °C). ECM uses HO2S No. 1 voltage to determine exhaust gas oxygen concentration during engine operation. Low voltage indicates a lean exhaust mixture and a higher voltage indicates a rich exhaust mixture. HO2S No. 1 works similar to a non-heated sensor, except HO2S No. 1 is heated to operating temperatures to allow system to quickly enter closed loop operation.
Heated Oxygen Sensor No. 2
Heated Oxygen Sensor (HO2S) No. 2 is mounted just after catalytic converter. HO2S No. 2 operates similar to HO2S No. 1 and is used by ECM to monitor catalyst efficiency. HO2S No. 2 is normal when its activity appears lazy or inactive, indicating converter is functioning properly.
Intake Air Temperature Sensor
Intake Air Temperature (IAT) sensor is located on side of air cleaner housing. IAT sensor is a thermistor which changes resistance with respect to temperature. High temperature causes low resistance. Low temperature causes high resistance. A reference voltage (supplied and monitored by ECM) is modified by sensor resistance. ECM uses this information to help control fuel injector(s), ignition timing and EGR operation.
Manifold Absolute Pressure Sensor
Manifold Absolute Pressure (MAP) sensor is connected to ECM by a 3-wire harness and to engine by a manifold vacuum hose. MAP sensor has an internal mechanical resistor which varies resistance based on changes in engine load (manifold vacuum). As internal resistance varies, return voltage signal to ECM varies. ECM interprets this voltage change as changes in engine load and uses this signal to help determine control of fuel injectors and other various sensors and switches.
Mass Airflow Sensor
Mass Airflow (MAF) sensor is located between air cleaner and throttle body. MAF sensor consists of a thermal resistor, metering duct and control circuit. Sensor uses thermal resistor to detect amount of air drawn into engine and sends information to ECM as a current signal. ECM uses this signal to control fuel injectors.
Power Steering Pressure Switch
ECM applies and monitors reference voltage to PSP switch. When steering wheel is turned, pressure switch closes, pulling reference voltage low. ECM uses this signal to help determine control of idle speed control system.
Throttle Position Sensor
Throttle Position (TP) sensor is connected to the throttle valve, and detects throttle valve opening. ECM supplies throttle position sensor with a 5-volt reference signal. Sensor contains a potentiometer (variable resistor) that returns a varying voltage back to ECM based on throttle position. ECM uses these signals to help determine control of air/fuel ratio during acceleration, deceleration and idle.
Park/Neutral Position Switch (A/T Only)
Park/Neutral Position (PNP) switch is located on transmission, next to shift linkage. PNP signal is sent from Transmission Control Module and sends a voltage signal to ECM when transmission is in Reverse, Drive, 2 or Low positions. ECM uses this signal to control fuel injectors, idle control system and ignition timing.
Vehicle Speed Sensor
Vehicle Speed Sensor (VSS) consists of a reed switch and magnet mounted on transmission. As magnet rotates within VSS, magnet causes reed switch to turn on and off. Switching action increases or decreases in proportion with vehicle speed. ECM supplies and monitors a voltage signal to VSS. ECM uses this signal to help determine control of idle speed control system as well as other control devices.
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 the system indicated after component.
Canister Purge Valve
See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS.
Malfunction Indicator Light
See SELF-DIAGNOSTIC SYSTEM .
EGR Solenoid Vacuum Valve
See EXHAUST GAS RECIRCULATION under EMISSION SYSTEMS.
Fuel-Cut System
See FUEL CONTROL under FUEL SYSTEM.
Fuel Injector(s)
See FUEL CONTROL under FUEL SYSTEM.
Fuel Pump Relay
See FUEL DELIVERY under FUEL SYSTEM.
Heated Oxygen Sensor Heater
See FUEL CONTROL under FUEL SYSTEM.
Idle Air Control System
See IDLE SPEED under FUEL SYSTEM.
Ignition Control System
See IGNITION TIMING CONTROL SYSTEM under IGNITION SYSTEM.
Torque Converter Clutch Relay Control
See TRANSMISSION CONTROL under MISCELLANEOUS CONTROLS.
Transmission Control Module
See TRANSMISSION CONTROL under MISCELLANEOUS CONTROLS.
Fuel Pump
Electric fuel pump is located in fuel tank. Fuel pump receives power when ECM provides ground to fuel pump relay. When power is supplied to fuel pump, motor and impeller inside pump turn. This causes a pressure difference to occur between both sides of impeller. When fuel is drawn through fuel pump inlet port, pressure is increased and discharged through outlet port.
The fuel pump also incorporates a relief valve to prevent excessive rise of discharge pressure and a check valve to keep residual pressure in fuel feed line when fuel pump is not activated.
Fuel pump relay is energized based upon ignition switch and RPM inputs. Power for fuel pump is supplied by main relay, which receives its power from FI fuse. Main relay is energized for several seconds by ECM when ignition is turned on. While engine is cranking or running, ECM maintains relay operation.
Fuel Pressure Regulator
Fuel pressure regulator is a spring/vacuum operated diaphragm-type relief valve which maintains a constant regulated fuel pressure under all vehicle operating modes. When manifold vacuum is high (low fuel requirements), diaphragm is drawn in, counteracting spring pressure and routing excess fuel back to fuel tank. When manifold vacuum decreases (engine load), spring pressure overcomes vacuum, closing off fuel tank return line. This maintains appropriate pressure and volume to injector(s) under different operating conditions.
All models use Sequential Multiport Fuel Injection (SFI), which incorporates fuel injectors mounted in a fuel rail assembly. When solenoid coil of fuel injector is energized by ECM, coil becomes an electromagnet. (Scheme 5) This lifts injector plunger, allowing fuel under pressure to be injected into cylinder head. Since fuel pressure is relatively constant, air/fuel mixtures are controlled by injector pulse width ("on" time). ECM determines proper pulse width based upon input signals received from various sensors and switches.
Scheme 5
Fuel injector triggering and timing is determined by ECM based upon ignition signals from Camshaft Position (CMP) sensor. Since ECM interprets CMP sensor signal as an indication of spark presence, fuel injector triggering will cease if CMP sensor signal is lost.
Battery Voltage Compensation
A drop in battery voltage directly affects pulse width of injector(s). As battery voltage drops, pulse width decreases. This causes a leaner air/fuel mixture than desired. To compensate for this, ECM monitors battery voltage. If battery voltage drops, ECM will increase injector pulse width.
The fuel-cut system will stop fuel injection during deceleration to prevent excess fuel build-up during periods when oxygen is insufficient for combustion (i.e., closed throttle, high RPM). Fuel-cut system will also deactivate injectors when engine speed exceeds a predetermined RPM to prevent engine damage due to excessive engine speed. As engine speed drops back down, injection will once again occur.
An electrical heating element is located inside oxygen sensor to bring oxygen sensor up to operating temperature quickly. When vehicle is cold, ECM grounds oxygen sensor heating element circuit. Power to sensor is provided when ignition is on.
Idle Air Control Valve
An air passage by-passing throttle valve is provided to route intake air directly into intake manifold. ECM-energized IAC valve regulates airflow through this passage. IAC valve is located on side of throttle body.
Air is allowed to pass through IAC valve when it is energized. Solenoid portion of valve is energized whenever idle speed drops to less than desired RPM due to engine load (i.e., electrical, A/C, P/S, automatic transmission in Drive, etc.). IAC valve is also energized each time engine is started and during periods of deceleration (to compensate for rich mixtures caused by a fully closed throttle). Duration of IAC valve operation is dependent on coolant temperature.
Fast Idle Cam
Fast idle cam is installed on the throttle body to maintain adequate engine speed while the engine is cold. It is operated by a volumetric change in wax located inside the thermo-element. The thermo-element is operated by engine coolant temperature.
ELECTRONIC IGNITION SYSTEM
All models use a distributorless ignition system. (Scheme 6), (Scheme 7) or (Scheme 8). All models engines use an ignition coil and igniter assembly mounted on top of each spark plug.
ECM relies on signals from Camshaft Position (CMP) sensor, Throttle Position (TP) sensor, Electronically Controlled Transmission (ECT) sensor and Mass Air Flow (MAF) sensor to control ignition spark. See INPUT DEVICES . Spark is achieved by ECM triggering igniter and in turn igniter grounding and opening ignition coil circuit.
Scheme 6
Scheme 7
Scheme 8
Ignition timing is controlled by ECM based upon sensor input signals. ECM controls ignition timing to a precise point by matching vehicle operating conditions to preprogrammed timing advance specifications stored in ECM memory.
Signals generated by Camshaft Position (CMP) sensor are transmitted to ECM. These signals are used in ECM calculations along with input signals from Engine Coolant Temperature (ECT) sensor, Knock Sensor (KS), Mass Airflow (MAF) sensor, Manifold Absolute Pressure (MAP) sensor, Throttle Position (TP) sensor, Closed Throttle Position (CTP) switch, Vehicle Speed Sensor (VSS) and monitored battery voltage.
Knock Control Compensation
Ignition timing is controlled by ECM based upon sensor input signals. When knock sensor (if equipped) detects engine knock, compensation is added, so as to recover from a knocking state immediately.
EXHAUST GAS RECIRCULATION
To lower oxides of nitrogen (NOx) exhaust gas emissions, an EGR system is used. EGR system introduces exhaust gases into intake system. Exhaust gases are noncombustible gases which, when combined with incoming air/fuel mixture, lower peak combustion chamber temperatures.
EGR Control
EGR valve is controlled by ECM using a stepper motor attached to EGR valve. ECM uses signals from Camshaft Position (CMP) sensor, Engine Coolant Temperature (ECT) sensor, Mass Airflow (MAF) sensor and Vehicle Speed Sensor (VSS) to determine control of stepper motor.
EVAPORATION EMISSION CONTROL SYSTEM
To identify EVAP control system components, see appropriate illustration: (Scheme 9), (Scheme 10), (Scheme 11) or (Scheme 12).
Scheme 9
Scheme 10
Scheme 11
Scheme 12
Emission Control System Description
Evaporative Emission (EVAP) control system's role (with On-board Refueling Vapor Recovery System), is to prevent fuel vapor from emitting into the atmosphere. The vapor produced in fuel tank is stored in the EVAP canister. While filling fuel vapor in fuel tank flows to the EVAP canister through EVAP vapor control valve and is stored there. When fuel tank becomes full, a float in the vapor control valve works to close vapor passage, rejecting further refueling. When fuel tank is filled with fuel, the vapor produced in the fuel tank passes through the tank pressure control valve and flows into the EVAP canister through the refuel vapor control valve and is stored there. When fuel tank is not filled with fuel the vapor produced in the fuel tank flows into the EVAP canister through the refuel vapor control valve and is stored there. When the EVAP canister purge valve opens, fuel vapor stored in EVAP canister is drawn into the intake manifold together with air coming in through the suction filter and burned. EVAP canister purge valve is controlled by ECM according to signals from various sensors. When engine is at normal operating temperature, throttle valve is open wider than closed throttle position and engine is operating in closed loop mode, ECM controls ON/OFF (open/close) switching of EVAP canister purge valve at a constant rate of 10 times/sec. Length of EVAP purge valve On time depends on; engine speed, engine load and concentration of fuel vapor in purge line (fuel vapor concentration is calculated based on short term fuel trim and vapor purge rate) so as to prevent air/fuel mixture from being changed suddenly. The EVAP canister vent valve and the fuel tank pressure sensor are among component parts installed so that ECM diagnoses leakage of fuel vapor from EVAP control system. The EVAP canister vent valve is usually open, but is closed by ECM when checking for EVAP system leakage.
EVAP Canister
Vapors generated in fuel tank pass through a check valve and enter EVAP canister where charcoal absorbs and stores fuel vapors. Canister is purged or cleaned by air drawn through filter at bottom of canister and sucked into intake manifold through purge control valve and purge line. Throttle body vacuum is applied to canister purge control valve to open valve under following conditions
- Engine speed is greater than 1500 RPM.
- Engine is at operating temperature.
EVAP Canister Purge Valve
ECM controls EVAP canister purge valve according to signals from various sensors. When ECM signals EVAP canister purge valve, fuel vapors flow from charcoal canister into combustion chambers for burning.
EVAP Canister Air Valve
When ECM signals canister purge valve, fuel vapors flow from charcoal canister into combustion chambers for burning. A condition then exist, where after, EVAP canister is purged or cleaned by air drawn through filter and EVAP canister air valve. Also ECM signals EVAP canister air valve ON (closed) when specific conditions are met to run a leak detection monitor.
Fuel Vapor Separator
When engine is not running, vapor from expanding fuel in fuel tank collects in fuel vapor separator. Fuel which condenses in fuel vapor separator returns to fuel tank. Fuel vapor flows from fuel vapor separator into charcoal canister where it is contained by activated charcoal. When engine is started, ported vacuum purges stored vapors from canister.
Fuel Tank Pressure Control Valve
Fuel tank pressure or vacuum is controlled by Fuel Tank Pressure Control Valve (FTPCV). When fuel tank pressure reaches a specified value, FTPCV opens and allows fuel vapors to enter EVAP canister. When fuel tank pressure becomes negative and reaches a specified value, FTPCV opens and allows outside air to flow into fuel tank.
POSITIVE CRANKCASE VENTILATION
PCV system consists of a crankcase hose from intake manifold to PCV valve in rocker cover. System draws crankcase blow-by gases (hydrocarbons) into air induction system rather than allowing them to escape to atmosphere. Crankcase gases are mixed with air/fuel mixture and burned in combustion chamber.
SELF-DIAGNOSTIC SYSTEM
When a system fault occurs, MIL (check engine light) on dash will illuminate to inform driver a problem exists. Light will remain ON until fault goes away or system is serviced. If fault goes away (system parameter returns to normal operation) before it is serviced, MIL will go out. Related fault code will still remain in ECM memory until cleared. Stored codes may later be accessed and identified by counting flashes of MIL or accessing Data Link Connector (DLC) with appropriate scan tool.
Note. MIL may also be referred to as CHECK ENGINE or SERVICE ENGINE SOON light.
All vehicles are equipped with a Malfunction Indicator Light (MIL) located on instrument panel. MIL will illuminate when ignition switch is turned to ON position (bulb check) and engine is not running. Light should not flash at this time and should go out when engine is started.
MISCELLANEOUS CONTROLS
Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.
This signal is sent from A/C amplifier to ECM. ECM uses this signal to detect when A/C is operating and sends a signal to Idle Air Control (IAC) valve or Idle Speed Control (ISC) actuator to increase idle speed.
Transmission Control Module (TCM) communicates with ECM and various engine sensors to help control shift points and torque converter lock-up to achieve maximum performance while maintaining optimal fuel economy.
Transmission Signal
After receiving throttle position signal from throttle position sensor, ECM converts signal into duty signal (voltage signal) and sends it to transmission control module. The transmission control module uses this information for controlling 2nd and 3rd gear shifts and torque converter clutch lock-up.
Torque Converter Clutch (TCC) relay controls TCC solenoid valve operation using signals from various engine sensors. TCC relay will only turn on when the following conditions are met
- Engine running
- Engine coolant near operating temperature (varies between models).
- Throttle valve open (degree of opening varies between models).
- Brake not applied (brake switch off).
- Vehicle speed more than specified mph (varies between models).
- 4WD LOW switch OFF (Grand Vitara, Vitara and XL-7).