Engine Controls - Theory & Operation: Other Saab 9-3 I

TURBOCHARGERS

On all models, turbocharger and wastegate assembly are mounted on exhaust manifold. At idle and light throttle, turbocharged engine operates like a standard engine. When engine speed is raised, increased exhaust gas flow spins impeller and turbine at a higher rate of speed, causing intake manifold to go from a negative pressure (vacuum) to a positive pressure (boost).

A wastegate is used on all 4-cylinder engines and is the system safety valve, preventing excessive boost pressure which can cause engine damage. A signal from ECM energizes a solenoid, which opens wastegate to control optimum boost pressure. In the event of control system failure, wastegate will open automatically to limit boost pressure.

System also incorporates a bypass valve to reroute boost pressure back to inlet side of turbo during deceleration. When throttle is suddenly closed, boost pressure between turbo compressor outlet and throttle valve rises sharply. This causes violent pulsations to occur in compressor inlet and outlet, and compressor damage can occur. By rerouting boost pressure back in front of the turbo, these pulsations are rendered harmless.

TRIONIC ENGINE MANAGEMENT SYSTEM

Trionic engine management system controls idle speed, fuel, turbo boost and ignition from one Engine Control Module (ECM). Mass air flow control is achieved by regulating turbocharger boost pressure on Trionic T-5 and Trionic T-7 4-cylinders, and throttle position on T-7 V6 engines. Fuel injection system control relies heavily on HO2S, Engine Coolant Temperature (ECT), Throttle Position (TP) Sensor and Mass Airflow (MAF) sensors to regulate fuel injector opening and duration times. Several other sensors are used to fine-tune EFI system. T-5 system uses an Idle Air Control (IAC) valve to regulate idle speed, while T-7 uses ECM to control throttle position at idle. T-7 also uses pedal position sensors to regulate throttle position, and is not directly connected to accelerator pedal unless a throttle-related malfunction occurs. Then, a limp-home solenoid directly links throttle with gas pedal.

Each spark plug has an individual coil that is integrated into ignition discharge module, which sits on top of the engine. Ignition timing is established by ECM by measuring resistance of each spark plug. As fuel in the cylinders is compressed and ionization of fuel molecules takes place, resistance across spark plug electrode drops. At a predetermined point, the ECM uses resistance drop to trigger ignition. Because resistance is also affected by knocking or pinging, ignition timing, fuel system and turbo boost can all be controlled in this manner. The need for Camshaft Position (CMP) sensor or Knock Sensor (KS) is eliminated.

When ignition is switched on, both main relay and fuel pump relay operate for a few seconds. As soon as ECM senses that crankshaft has begun to rotate, coolant temperature dependent fuel injection takes place through injectors simultaneously. This enables short starting time to be achieved. If engine is started and shortly afterward switched off again, a fresh pre-injection sequence will be obtained if 45 seconds is allowed to pass with ignition switched off.

COMPUTERIZED ENGINE CONTROLS

ENGINE CONTROL MODULE (ECM)

On 9-3 models, ECM is located above right side kick panel, behind glove box. On 9-5 models, ECM is located in engine compartment, between inner and outer firewall below windshield, on passenger side. For ECM pin and wire color identification, see appropriate SELF-DIAGNOSTICS article.

ECM controls all engine functions: fuel injection, ignition timing, turbo boost pressure, idle speed, emission control, combustion analysis and self-diagnostics. For a description of ECM controlled functions, see TRIONIC ENGINE MANAGEMENT SYSTEM .

Note. Components are grouped into 2 categories. The first category is INPUT DEVICES , which are components that control or produce voltage signals monitored by ECM. The second category is OUTPUT SIGNALS , which are controlled by 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 devices include

A/C Switch

When A/C is on, switch sends a signal to the ECM. To compensate for increased load, ECM sends a signal to Idle Air Control (IAC) valve on T-5 or throttle control motor on T-7 to increase idle speed.

Charge Air Absolute Pressure (CAAP) Sensor

CAAP sensor works in conjunction with IAT sensor to determine air charge density, and is connected to intake manifold by a hose before throttle body. It receives a 5 volt reference signal from ECM, and returns a varying voltage depending on intake air pressure between turbocharger and throttle valve.

Crankshaft Position (CKP) Sensor

CKP sensor is mounted in side of engine block, and is positioned approximately .04" (1 mm) from slotted ring mounted on crankshaft. No adjustment provision exists. Sensor generates a voltage signal to ECM, and slotted ring determines frequency of signal. Two ribs are missing after 58th rib on slotted ring, giving ECM a reference point to determine crankshaft position. See appropriate SYSTEM & COMPONENT TESTING article for further diagnostic procedures.

Engine Coolant Temperature (ECT) Sensor

On Trionic T-5 systems, ECT is located in intake manifold between cylinders No. 3 and 4. On Trionic T-7 systems, ECT is located on left side of cylinder head. Sensor transmits an engine temperature signal to ECM. If ECM fails to receive this signal, it defaults to a substitute temperature value equal to intake air temperature on startup. It then increases that value by 1.8°F (1°C) for every 150 revolutions of the crankshaft until a value equal to 194° (90°C) is reached.

Gear Selector Switch

A/T models are equipped with a switch that signals ECM whenever transmission is in a range other than Park or Neutral. To compensate for increased load, ECM sends a signal to Idle Air Control (IAC) valve on T-5 or throttle control motor on T-7 to increase idle speed.

Heated Oxygen Sensor (HO2S)

All models are equipped with 2 HO2S sensors. They are located in exhaust before and after catalytic converter. These sensors measure quantity of oxygen left in exhaust gas after combustion. ECM uses signal from HO2S in front of converter to adjust air/fuel mixture. HO2S behind catalytic converter is used to monitor converter efficiency by comparing readings from both sensors. If voltage signals from both sensors are the same, ECM sets a DTC and turns on CHECK ENGINE light, due to the fact that catalytic converter is not affecting oxygen content of exhaust. The electric heating element built into each sensor provides improved cold engine driveability, and ensures that HO2S operating temperature is maintained at idle.

Intake Air Temperature (IAT) Sensor

This sensor is used together with Charge Air Absolute Pressure (CAAP) sensor to provide air charge density information to ECM. IAT sensor is located on the intake air duct leading to the throttle body.

Manifold Absolute Pressure (MAP) Sensor

This sensor is used to compensate for inaccurate mass air flow input signals that can vary during rapid throttle changes. Map sensor receives a 5 volt reference signal from ECM and returns a varying voltage depending on intake manifold pressure. Map sensor is also used to modify pulse-width modulation of EVAP system purge valve during changes in manifold vacuum/pressure.

Mass Airflow (MAF) Sensor (9-3 With Trionic T-7 & 9-5)

The MAF sensor is located between the air cleaner and throttle body. Sensor contains 2 PTC resistors which are heated electrically to 428°F (220°C). When airflow increases, heating element requires higher voltage to maintain temperature. The voltage required is converted into ground pulses, which increase in frequency as air flow increases. ECM uses ground pulse frequency to calculate mass air flow.

Throttle Position (TP) Sensor (9-3 With Trionic T-5)

TP sensor is located on side of throttle body. TP sensor receives a 5 volt reference signal from ECM. It is connected to throttle, and returns a voltage proportional to throttle position. At idle, return voltage is about .5 volts and at full throttle, it is about 4.5 volts. Return voltage signal is used by ECM to enrichen fuel mixture during acceleration, and shut off fuel delivery during deceleration until a specified RPM is reached. TP sensor signal is also used to adjust turbo boost pressure.

Throttle/Pedal Position Sensors (9-3 With Trionic T-7 & 9-5)

These sensors are located on throttle body. There are 2 throttle position sensors, and also 2 pedal position sensors. These are used to compare requested throttle position with actual throttle position. One sensor returns a low reference voltage at idle while other sensor returns a high reference voltage (around 5 volts). At wide open throttle, sensor values are reversed. The 2 voltage signals are combined and are inputted to PCM. Return voltage should always be around 5 volts. If voltage is not as specified, a Diagnostic Trouble Code (DTC) will set, and throttle control will go into limp-home mode (throttle angle is no longer controlled by PCM). See appropriate SELF-DIAGNOSTICS article for trouble shooting information.

Vehicle Speed Sensor (VSS)

ECM receives vehicle speed signal from ABS control module 29 times per 1 wheel rotation. On M/T vehicles with T-7, this is used to limit torque applied in reverse and 1st gears by controlling throttle angle, regardless of gas pedal position. On all models, in gears 2, 3, 4 and 5, ECM uses VSS to activate fuel shutoff on deceleration. It is also used to limit top speed, and to prevent idle speed control when vehicle is moving. See appropriate SYSTEM & COMPONENT TESTING article for further diagnostic procedures.

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 signal component, refer to system indicated after component.

Canister Purge Valve

See EVAP CANISTER PURGE VALVE under EMISSION SYSTEMS.

Fuel Pump Relay

See FUEL PUMP RELAY under FUEL SYSTEM.

Fuel Injectors

See FUEL INJECTORS under FUEL SYSTEM.

See HEATED OXYGEN SENSOR (HO2S) under FUEL SYSTEM.

Ignition Coil(s)

See IGNITION SYSTEM .

Malfunction Indicator Light (MIL)

See MALFUNCTION INDICATOR LIGHT (MIL) under SELF-DIAGNOSTIC SYSTEM.

Self-Diagnostics

See SELF-DIAGNOSTIC SYSTEM .

Wastegate Solenoid

See TURBOCHARGERS under AIR INDUCTION SYSTEM.

FUEL DELIVERY

The fuel system consists of a fuel tank, fuel pump, fuel lines, filter and a fuel pressure regulator. Fuel is supplied to each injector at a constant pressure.

Fuel Pressure Regulator

Fuel pressure regulator, located on fuel rail, controls fuel pressure at fuel injectors. Pressure is raised or lowered in direct proportion to engine vacuum or turbo boost present in intake manifold. Under boost conditions, fuel pressure is increased to offset positive pressure in intake system. Excess fuel bypasses injectors and returns to fuel tank.

Fuel Pump

Fuel pump is located inside tank. Fuel is strained through a mesh screen before entering the pump. A check valve, located on outlet side of pump, maintains pressure within the fuel system when engine is off. Fuel pump can be serviced through access panel under rear seat cushion.

Fuel pump relay supplies power to fuel pump and HO2S heater. When ignition is turned on, relay energizes for one second to build up fuel pressure before engine cranking. Relay is turned on and off by ECM.

ECM

ECM processes pulses from the crankshaft position sensor to determine basic fuel injection timing. It also processes signals from other sensors for calculating pulse duration to control fuel mixture.

Fuel injectors, located in intake manifold, spray atomized fuel directly toward associated intake valves. All injectors are supplied with fuel from a common fuel manifold. On 4-cylinder engines with T-7, passages in intake manifold feed a stream of air to tip of spray nozzle in order to better atomize fuel at point of injection. Signals from ECM control injection pulse duration.

The ECM sends a signal to a heating element in the oxygen sensor. The function of the heating element is to more quickly bring the sensing element to operating temperature during cold engine operation. It also keeps HO2S hot while idling to prevent system from going back into open loop.

Once sensor is up to operating temperature, a chemical process takes place as exhaust passes the sensing element, and a varying voltage is produced as a result. The voltage is dependent upon the level of oxygen in the exhaust. When the mixture is rich, there is very low oxygen content, and the HO2S produces as high as .9 volts. Likewise, when the mixture is lean, a greater amount of oxygen is present and HO2S produces as low as .1 volts. The ECM is able to quickly compensate for a rich or lean mixture based largely on HO2S input.

IDLE SPEED

On T-5 systems, idle speed is ECM-controlled by opening or closing an Idle Air Control (IAC) valve. On T-7 systems, ECM adjusts throttle opening to maintain desired engine RPM and does not use an IAC. There are no adjustment provisions on either system. If idle speed is either too high or too low, ECM will store a DTC and turn CHECK ENGINE light on.

IGNITION SYSTEM

Ignition system is a type of DIS ignition, but does not use a waste spark method. Instead, each spark plug acts as a variable resistor to trigger the coils to fire. Each spark plug has an individual coil sitting inside the ignition control module on top of engine. For a complete description of operation, see TRIONIC ENGINE MANAGEMENT SYSTEM .

THREE-WAY CATALYTIC CONVERTER (TWC)

All vehicles are equipped with a TWC. This device reduces oxides of nitrogen, hydrocarbons and carbon monoxide by placing a ceramic or metal material coated with rhodium, platinum or palladium in exhaust stream. These substances act as a catalyst by changing exhaust composition from harmful gases to carbon dioxide, water and nitrogen without being affected by process themselves.

FUEL EVAPORATIVE SYSTEM

Note. Starting in 1998, On-board Refueling Vapor Recovery (ORVR) systems became mandatory on all U.S. models. The following components are used to eliminate the loss of hydrocarbons to the atmosphere from fuel tank and system.

EVAP Vapor Canister

Fumes from fuel tank are stored in a charcoal canister when vehicle is not running. When engine is started, intake manifold vacuum purges fumes through a canister purge solenoid after receiving signal from ECM.

Fuel Tank Pressure (FTP) Sensor

FTP sensor is mounted on top of fuel tank and compares tank pressure to atmospheric pressure. When the two are the same, sensor returns a voltage value of approximately 2.5 volts the ECM. Return voltage fluctuates up or down from there, depending on whether fuel tank is under pressure or vacuum. For diagnostic procedures, see DTC P0452-P0453: FUEL TANK PRESSURE (FTP) SENSOR CIRCUIT under DIAGNOSTIC TESTS in appropriate SELF-DIAGNOSTICS article.

Fuel Shutoff (Rollover) Valve

The rollover valve is in the fuel evaporation line on top of fuel tank and closes if vehicle rolls over.

Fuel Tank Float Valve

During refueling, vapors are pressed through float valve and into vapor canister. When tank is full, a spring-loaded float closes valve to prevent liquid fuel from reaching vapor canister. Valve also closes in event of a rollover.

Fuel Tank Non-Return Valve

Non-return valve is a one-way check valve that only allows fuel to flow towards tank and not back. This prevents fuel from spitting back out of filler nozzle while refueling.

EVAP Shutoff Solenoid Valve

The EVAP canister fresh air supply is regulated by shutoff solenoid valve and is normally in open position. The valve is closed only during a tank integrity test and is used for OBD II diagnostics. See appropriate SYSTEM & COMPONENT TESTING article for further diagnostic procedures.

EVAP Canister Purge Valve

The purge valve is located in line between the EVAP canister and intake manifold. Its purpose is to regulate the amount of air and hydrocarbons purged from the EVAP canister. Valve is turned on at various times by ECM, and is also used during tank integrity test to check for leaks.

POSITIVE CRANKCASE VENTILATION

All vehicles have a completely closed crankcase ventilation system. Crankcase fumes are drawn into the intake manifold by manifold vacuum. Under load, the turbocharger starts to pressurize intake manifold. A venturi placed before the turbo inlet creates vacuum under load conditions and fumes are diverted into venturi in order to maintain lower pressure in crankcase.

Note. MIL is also known as CHECK ENGINE light.

All vehicles are equipped with a MIL located on instrument panel. MIL will come on when ignition is turned on (bulb check), and when ECM detects any abnormalities in fuel system or emission controls during normal operation. For additional information, see appropriate SELF-DIAGNOSTICS article.

MISCELLANEOUS CONTROLS

Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.

A/C CLUTCH

At full throttle, ECM opens ground circuit to A/C clutch to inhibit A/C operation.

Cooling Fan Motor (9-3)

All 9-3 models have one cooling fan. Depending on market location, fan will have either 1 or 2 speeds which are controlled by DICE (Dashboard Integrated Control System) based on inputs from coolant temperature, A/C pressure and status (on or off), vehicle speed and outside temperature. Failure of fan to operate may result in overheating and detonation. Cooling fan can come on up to 20 minutes after engine is turned off and can continue to run at low speed for up to 3 1/2 minutes.

Cooling Fan Motor (9-5)

Vehicles without A/C have one 2-speed fan mounted behind radiator that is controlled by Trionic T-7 Engine Management System based on coolant temperature. Cars with A/C have two 2-speed fans controlled by DICE (Dashboard Integrated Control System) based on inputs from coolant temperature, A/C pressure, vehicle speed and outside temperature. Failure of fan to operate may result in overheating and detonation. Cooling fan(s) can continue to run at low speed for up to 3 1/2 minutes after engine is shut off.

Cooling Fan Relays (9-3)

One cooling fan relay is used for single-speed fan equipped vehicles, and two relays are used on cars with 2-speed fans, one for low speed and one for high speed. They are located in power distribution box, on right rear of engine compartment. Relay(s) are controlled by DICE (Dashboard Integrated Control System) via coolant temperature signals, A/C pressure, vehicle speed and outside temperature.

Cooling Fan Relays (9-5)

Two cooling fan relays are used on cars without A/C, one for low speed and one for high speed. On cars with A/C, three relays are used. They are located in power distribution box, on right rear of engine compartment behind battery. All relays are controlled by DICE (Dashboard Integrated Control System) via coolant temperature signals (also A/C pressure, vehicle speed and outside temperature on A/C equipped cars) received from Trionic Engine Management System.