COMPUTERIZED ENGINE CONTROLS
Computerized engine control system consists of a Powertrain Control Module (PCM), various sensors (inputs), control devices and actuators (outputs), and related wiring which links system together. PCM 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, PCM 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 Tech 1 or other OBD II compatible scan tool. DLC is located under instrument panel, accessible from driver's side.
PCM incorporates a fail-safe (limp-in) mode. If a fault occurs during vehicle operation, PCM will substitute a predetermined value and/or signal for continued operation. Driving performance will be affected, but vehicle may still be driven. When PCM detects a system fault, Malfunction Indicator Light (MIL) will flash or illuminate steadily to notify driver of a developing problem.
POWERTRAIN CONTROL MODULE (PCM)
Note. See PIN VOLTAGE CHARTS article and appropriate wiring diagram in WIRING DIAGRAMS article for PCM connector and wire terminal identification.
PCM Voltage Supply
PCM is located behind glove box. PCM power is sent from main relay to following terminals
- On Esteem and Swift, 26-pin connector terminals No. 2 and 15.
- On Vitara, 35-pin connector terminal No. 9.
- On Grand Vitara 2.5L V6, 35-pin connector terminal No. 8.
PCM backup power is sent from fuse box to following terminals
- On Esteem and Swift, 26-pin connector terminals No. 14.
- On Vitara, 35-pin connector terminal No. 2.
- On Grand Vitara 2.5L V6, 35-pin connector terminal No.35.
Note. Components are grouped into 2 categories. First category is INPUT DEVICES , which are components that control or produce voltage signals monitored by PCM. Second category is OUTPUT SIGNALS , which are components controlled by PCM.
INPUT DEVICES
Note. See PIN VOLTAGE CHARTS article and appropriate wiring diagram in WIRING DIAGRAMS article for PCM connector and wire terminal identification.
A/C Signal
See MISCELLANEOUS CONTROLS .
Camshaft Position (CMP) Sensor
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). PCM uses this signal to determine position of No. 1 and 3 pistons.
Crankshaft Position (CKP) Sensor
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 PCM and is used to monitor misfire conditions.
Electric Load Signal
This signal is sent to PCM from headlights, clearance lights, heater fan, stop lights or rear window defogger as one or more accessory is turned on. PCM uses this signal to control operation of idle control system to compensate for electrical load on engine.
Engine Coolant Temperature (ECT) Sensor
ECT sensor thermistor changes resistance with respect to coolant temperature. High temperature causes low resistance. Low temperature causes high resistance. A reference voltage (supplied and monitored by PCM) is modified by sensor resistance. PCM uses this information to control operation of various devices.
Engine Start Signal
This signal is sent from starter circuit to PCM as engine is cranked. PCM uses this signal to monitor when engine is cranking to activate fuel pump relay and fuel injector(s).
Fuel Tank Pressure Sensor
Fuel tank pressure sensor receives a 5-volt reference from PCM. As fuel tank pressure changes, resistance of sensor changes and sends a voltage signal back to PCM. PCM uses this signal to determine if a leak exists in EVAP system.
Heated Oxygen Sensor (HO2S) No. 1
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). PCM 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 (HO2S) No. 2
HO2S No. 2 is mounted just after catalytic converter. HO2S No. 2 operates similar to HO2S No. 1 and is used by PCM to monitor catalyst efficiency. HO2S No. 2 is normal when its activity appears lazy or inactive, indicating converter is functioning properly.
Intake Air Temperature (IAT) Sensor
On Esteem and Swift, IAT sensor is located on air cleaner pipe leading to throttle body. On Vitara and Grand Vitara, IAT sensor is located on side of air cleaner housing. On all models, air temperature sensor thermistor changes resistance with respect to temperature. High temperature causes low resistance. Low temperature causes high resistance. A reference voltage (supplied and monitored by PCM) is modified by sensor resistance. PCM uses this information to help control fuel injector(s), ignition timing and EGR operation.
Manifold Absolute Pressure (MAP) Sensor
MAP sensor is connected to PCM 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 PCM varies. PCM 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 (MAF) Sensor (Vitara & Grand Vitara)
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 PCM as a current signal. PCM uses this signal to control fuel injectors.
Power Steering Pressure (PSP) Switch
PCM applies and monitors reference voltage to PSP switch. When steering wheel is turned, pressure switch closes, pulling reference voltage low. PCM uses this signal to help determine control of idle speed control system.
Throttle Position (TP) Sensor
PCM supplies throttle position sensor with a 5-volt reference signal. Sensor contains a potentiometer (variable resistor) that returns a varying voltage back to PCM based on throttle position. PCM uses these signals to help determine control of air/fuel ratio during acceleration, deceleration and idle.
Transmission Range Switch (TRS) A/T Only
TRS is located on transmission, next to shift linkage. TRS switch is an on/off switch that turns on and sends a voltage signal to PCM when transmission is in Park or Neutral. PCM uses this signal to control fuel injectors and idle control system.
Vehicle Speed Sensor (VSS)
VSS consists of a reed switch and magnet mounted on transmission (in speedometer head on Swift M/T). As magnet rotates within VSS, magnet causes reed switch to turn on and off. Switching action increases or decreases in proportion with vehicle speed. PCM supplies and monitors a voltage signal to VSS. PCM uses this signal to help determine control of idle speed control system and up-shift indicator light on Swift.
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 (MIL)
See SELF-DIAGNOSTIC SYSTEM .
EGR Solenoid Vacuum Valve
See EXHAUST GAS RECIRCULATION (EGR) 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 (IAC) System
See IDLE SPEED under FUEL SYSTEM.
Ignition Control (IC) System
See IGNITION TIMING CONTROL SYSTEM under IGNITION SYSTEM.
Transmission Control Module (TCM)
See TRANSMISSION CONTROL under MISCELLANEOUS CONTROLS.
Fuel Pump
Electric fuel pump is located in fuel tank. Fuel pump receives power when PCM 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 PCM when ignition is turned on. While engine is cranking or running, PCM 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 4 fuel injectors mounted in a fuel rail assembly. MFI system injects fuel into each cylinder head intake port. When solenoid coil of fuel injector is energized by PCM, coil becomes an electromagnet. (Scheme 1) 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). PCM determines proper pulse width based upon input signals received from various sensors and switches.
Scheme 1
Fuel injector triggering and timing is determined by PCM based upon ignition signals from Camshaft Position (CMP) sensor. Since PCM 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, PCM monitors battery voltage. If battery voltage drops, PCM 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, PCM grounds oxygen sensor heating element circuit. Power to sensor is provided when ignition is on.
Idle Air Control (IAC) Valve
An air passage by-passing throttle valve is provided to route intake air directly into intake manifold. PCM-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.
ELECTRONIC IGNITION SYSTEM
All models use a distributorless ignition system. (Scheme 2)or (Scheme 3). Grand Vitara V6 engine uses an ignition coil and igniter assembly mounted on top of each spark plug. All other models use a waste-spark ignition with 2 ignition coil and igniter assemblies that fire 2 spark plugs simultaneously.
PCM 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 PCM triggering igniter and in turn igniter grounding and opening ignition coil circuit.
Note. Esteem and Swift use a manifold absolute pressure (MAP) sensor in place of a (MAF) sensor.
Scheme 2
Scheme 3
Ignition timing is controlled by PCM based upon sensor input signals. PCM controls ignition timing to a precise point by matching vehicle operating conditions to preprogrammed timing advance specifications stored in PCM memory.
Signals generated by Camshaft Position (CMP) sensor are transmitted to PCM. These signals are used in PCM calculations along with input signals from Engine Coolant Temperature (ECT) sensor, 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.
EMISSION SYSTEMS
For additional information, see EMISSION APPLICATIONS and VACUUM DIAGRAMS articles.
EXHAUST GAS RECIRCULATION (EGR)
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 (Esteem, Vitara & Grand Vitara)
EGR valve is controlled by PCM using a stepper motor attached to EGR valve. PCM 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.
FUEL EVAPORATION SYSTEM
Note. To identify fuel evaporation system components, use appropriate illustration. see scheme 4or see scheme 5. No illustration is available for Grand Vitara 2.5L V6.
Charcoal Canister
Vapors generated in fuel tank pass through a check valve and enter charcoal 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.
PCM controls canister purge valve according to signals from various sensors. When PCM signals canister purge valve, fuel vapors flow from charcoal canister into combustion chambers for burning.
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.
Tank Pressure Control Valve
Fuel tank pressure or vacuum is controlled by tank pressure control valve. When fuel tank pressure reaches a specified value, tank pressure control valve opens and allows fuel vapors to enter EVAP canister. When fuel tank pressure becomes negative and reaches a specified value, tank pressure control valve opens and allows outside air to flow into fuel tank.
POSITIVE CRANKCASE VENTILATION (PCV)
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.
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. See PIN VOLTAGE CHARTS article and appropriate wiring diagrams in WIRING DIAGRAMS article for PCM connector and wire terminal identification.
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 PCM. PCM 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.
TCM communicates with PCM 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, PCM 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.