TURBOCHARGERS
| CAUTION | Because turbocharger impeller speeds can sometimes exceed 100,000 RPM, always allow a turbocharged engine to return to idle for several seconds before shutting off. If an engine is revved up before being shut down, the impeller will continue to spin at a high rate of speed and turbo bearing will run dry because of lack of engine oil pressure. |
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 increases under acceleration, 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 2.0L and 2.3L engines. This is the system's safety valve, preventing excessive boost pressure which can cause engine damage. A signal from ECM energizes the charge air control valve, which provides vacuum to a diaphragm that opens wastegate to control optimum boost pressure.
Models with 3.0L engines do not use a wastegate to control boost pressure. This is a low boost system, comprising of one turbocharger driven by a single engine bank. The bypass feature of this system is enough to control optimum boost pressure.
This system also incorporates a bypass valve to reroute boost pressure back to inlet side of turbo during deceleration. In de-energized state, the bypass valve control solenoid will allow intake manifold vacuum to be present at bypass valve. 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 using Engine Control Module (ECM). 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 fuel injection system. The Trionic engine management system uses ECM to control throttle position at idle. Trionic engine management system also uses pedal position sensors to regulate throttle body position. Throttle body is not directly connected to accelerator pedal unless a throttle-related malfunction occurs. Then, a limp-home solenoid directly links throttle body with accelerator 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 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, ECM uses the 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. ECM can substitute data for any malfunctioning input sensor except Crankshaft Position (CKP) sensor. ECM contains an integrated absolute pressure sensor. After ignition is turned off, all sensors (supplied with 5 volts) are active for an additional 15 minutes.
COMPUTERIZED ENGINE CONTROLS
| CAUTION | Electronic components used in control systems are designed to carry very low voltage. As little as a 30-volt charge created by static electricity can cause a total or degrading failure in ECM or other electronic components containing integrated circuits. Before servicing such components, ground yourself and ground work area to discharge stored static electricity. Repeat grounding process periodically during service procedure. |
ENGINE CONTROL MODULE (ECM)
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 Engine Performance wiring diagram in WIRING DIAGRAMS. The available input devices include
Absolute Pressure Sensor
Absolute pressure sensor is an integral part of the ECM. Information from the absolute pressure sensor is used by the ECM to correct charge air control valve ratio, correct EVAP canister purging ratio and protect turbo from overrevving. It also allows for blocking certain diagnoses at pressures lower than 72 kPa, and allowing certain diagnoses at pressures higher than 78 kPa.
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 throttle control motor on T-7 to increase idle speed.
Charge Air Pressure Sensor
Charge air pressure sensor works in conjunction with intake air temperature sensor to determine air charge density. Charge air pressure sensor is an integral part of the intake air temperature sensor. It receives a 5 volt reference signal from ECM, and returns a varying analog 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 0.02-0.05" (0.4-1.3 mm) from 60 tooth sprocket mounted on crankshaft. CKP sensor position is not adjustable. Sensor generates a voltage signal to ECM. Two teeth are missing after 58th tooth on sprocket, giving ECM a reference point to determine crankshaft position of 117 degrees before top dead center. Information form CKP sensor allows ECM to ground the fuel pump relay, and is also used to control ignition, fuel injection and knock detection.
Engine Coolant Temperature (ECT) Sensor
Sensor transmits an engine temperature signal to ECM. ECM sensor is a Negative Temperature Coefficient (NTC) type. ECM sensor receives a 5 volt reference signal from ECM trough a one kohm resistor integrated in ECM. ECT then returns a varying voltage depending on engine coolant temperature. If ECT sensor indicates that engine coolant temperature is lower than 19.4°F (-7°C), ECM will stop specific diagnosing procedure. If ECT sensor indicates that engine coolant temperature is higher than 140°F (60°C), ECM will start specific diagnosing procedure. If ECT sensor information is faulty, ECM defaults to a substitute temperature value equal to engine coolant temperature on start-up. It then increases that value by 1.8°F (1°C) for every 60 grams of air passing through the Mass Air Flow (MAF) sensor until a value equal to 194° (90°C) is reached. ECM uses ECT sensor information to control fuel injection duration and correct idle speed.
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 throttle control motor on T-7 to increase idle speed.
Heated Oxygen Sensor (HO2S)
All models are equipped with a primary heated oxygen (HO2S-1) and secondary heated oxygen (HO2S-2) sensors. They are located in exhaust before and after the catalytic converter. These sensors measure quantity of oxygen left in exhaust gas after combustion. ECM uses signal from HO2S-1 to adjust air/fuel mixture and HO2S-2 to monitor converter efficiency by comparing readings from both sensors. HO2S-2 is also used to correct for minor faults in HO2S-1. If voltage signals from both sensors are the same, ECM sets a DTC and turns on CHECK ENGINE light, indicating 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 all the time.
Intake Air Temperature (IAT) Sensor
IAT sensor is an integral part of the charge air pressure sensor. IAT sensor is a Negative Temperature Coefficient (NTC) type. IAT sensor receives a 5 volt reference signal from ECM through a 2.74 kohm resistor integrated in ECM. IAT then returns a varying voltage depending on intake manifold temperature. This sensor is used together with charge air pressure sensor to provide air charge density information to ECM. IAT sensor is used to modify pulse-width modulation of EVAP canister purge valve during changes in manifold vacuum/pressure. IAT sensor is also used to correct ignition timing. If IAT sensor indicates that intake air temperature is lower than 19.4°F (-7°C), ECM will stop specific diagnosing procedure. If IAT sensor indicates that intake air temperature is higher than 41°F (5°C), ECM will start specific diagnosing procedure. If IAT sensor information is faulty, ECM will substitute IAT sensor information with a value of 104°F (40°C).
Manifold Absolute Pressure (MAP) Sensor
This MAP 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 analog voltage depending on intake manifold pressure. MAP sensor is also used to modify pulse-width modulation of EVAP canister purge valve during changes in manifold vacuum/pressure.
Mass Airflow (MAF) Sensor
The MAF sensor contains 3 Positive Temperature Coefficient (PTC) resistors. 2 PTC resistors are used to measure air flow. They are connected in parallel in the airstream, and are heated electrically to 428°F (220°C) above incoming air temperature. The third is used to measure air temperature. 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. MAF sensor signals are a measurement of engine load. If a fault is detected in the MAF sensor circuit, substitute values will be used for intake pressure and intake air temperature.
Throttle/Pedal Position Sensors
This system is equipped with a redundant sensor system. These sensors are located on throttle body. There are 2 Throttle Position (TP) sensors, and 2 Pedal Position (PP) sensors. The TP sensor are connected to throttle spindle. When throttle position increases, TP sensor No. 1 voltage increases, TP sensor No. 2 voltage decreases, PP sensor No. 1 voltage decreases and PP sensor No. 2 voltage increases. These sensors 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 ECM. Voltage from TP sensor No. 1 is used by ECM as a value for current throttle position. Voltage from PP sensor No. 1 is used by ECM to measure driver's torque request. Return voltage (the sum of both PP sensors or TP sensors) 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 ECM). A sprocket spring loaded by the throttle arm return spring will release the throttle arm return spring when the limp-home solenoid is activated. This will disengage the throttle control motor and allow throttle operation via redundant accelerator cable. Accelerator pedal feel will not be affected when vehicle is in limp-home mode. The sprocket must be reset manually after repair and clearing of the Diagnostic Trouble Code (DTC). In case of PP sensor malfunction, maximum engine speed will be limited to 2200 RPM.
Vehicle Speed Sensor (VSS)
ECM receives vehicle speed signal from ABS control module 29 times per 1 wheel rotation. On M/T vehicles, 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.
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.
EVAP Canister Purge Valve
See EVAP CANISTER PURGE VALVE under EMISSION SYSTEMS.
Charge Air Control Valve
See TURBOCHARGERS under AIR INDUCTION SYSTEM.
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 .
Throttle Control Motor
The throttle control motor is a brushless motor controlled by the ECM.
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. On some models, 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 2.0L and 2.3L engines, passages in intake manifold feed a stream of air to tip of spray nozzle in order to better atomize fuel at point of injection and cool injectors. Signals from ECM control injection pulse duration. Injectors must not be rotated. Fuel injector connector must point straight up. If injectors are rotated, fuel will hit walls of the intake passages and affect emissions and driveability. If a fuel injector fault is present, closed loop operation will be cancelled.
The ECM sends a signal to a heating element in the oxygen sensor. The function of the heating element is quickly bring the sensing element to operating temperature during cold engine operation. It also keeps HO2S hot at proper temperature under any driving condition to prevent system from going back into open loop. The heating element of the secondary heated oxygen sensor (HO2S-2) is activated only after engine coolant temperature exceeds 86°F (30°C). To control heating element of HO2S, grounding circuit is pulse width modulated. The ECM estimates exhaust gas temperature based on load and engine speed. When exhaust gas temperature is high, heating element of HO2S is turned off to avoid damaging the HO2S.
Once sensor is up to operating temperature, a chemical/mechanical 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 0.9 volts. Likewise, when the mixture is lean, a greater amount of oxygen is present and HO2S produces as low as 0.1 volts. The ECM is able to quickly compensate for a rich or lean mixture based largely on HO2S input. The limits for correcting air fuel mixture during closed loop operation is between 1.25 volts (25 percent) and 0.75 volts (-25 percent).
In order to enter close loop operation, flowing conditions must be met
- Engine speed must exceed 500 RPM.
- Engine must have been running for 100-300 revolutions, depending on engine coolant temperature.
- HO2S voltage must have been less than 0.4 volts or more than 0.6 volts.
- At idle, engine coolant temperature must be more than 59-86°F (15-30°C), depending on engine staring temperature.
- During partial engine load, engine coolant temperature must be more than 50-86°F (10-30°C), depending on engine starting temperature.
- No fuel compensation for knocking or high load.
- Engine load must be more than 50 mg/c.
- No fuel compensation for load change when engine coolant temperature is less than 104°F (40°C).
IDLE SPEED
ECM adjusts throttle opening to maintain desired engine RPM and does not use an IAC. There are no adjustment provisions. If idle speed is either too high or too low, ECM will store a DTC and turn CHECK ENGINE light on. When ignition is turned off, main relay will remain on for 10 seconds to enable throttle valve motor to completely close throttle valve.
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 . During starting of vehicle, the ECM does not know if No. 1or No. 4 cylinder is at TDC. So it fires both cylinders simultaneously. Cylinder No. 2 and No. 3 are fired the same way.
AIR INJECTION SYSTEM (9-5 - 3.0L)
Air injection pump is an electric pump that is activated by the ECM. Air injection pump is used to pump ambient air into both exhaust manifolds in order to speed up the activation of the catalytic converter during cold starting. Additional fuel is supplied to compensate for the extra air.
Air pump will not start if battery voltage exceeds 16 volts. This is to prevent overloading the air pump. Air pump will not start if mass air flow is sufficient enough for normal combustion to heat up the catalytic converter. Air pump will start when engine is started provided the charge air temperature and engine coolant temperature are 16-86°F (-9-30°C).
Engine is allowed to rotate through 40-75 combustion cycles (depending on engine coolant temperature) before the air pump is turned on. Air pump will continue to run through another 15 combustion cycles after the system stopped calling for air pump operation.
When vehicle is started and engine coolant temperature is less than 86°F (30°C), the vehicle must have been turned off for at least 15 minutes before air pump will be activated.
Air injection system is equipped with one-way valves on each cylinder bank, to prevent exhaust gasses leaking from air injection system. They will close when pump operation stops.
THREE-WAY CATALYTIC CONVERTER (TWC)
| WARNING | DO NOT use leaded fuels, as lead coats the layers of converter and renders catalyst ineffective. |
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 carbon monoxide, hydrogen carbons and nitrogen oxide to carbon dioxide, water and nitrogen without being affected by process themselves.
EVAP 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 EVAP canister purge valve after receiving signal from ECM.
EVAP canister purge valves 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. EVAP canister purge valve is closed when de-energized.
EVAP Canister Purging
Under normal (non-boost) driving conditions, vapor is drawn through canister purge solenoid and a one-way check valve in to the intake manifold. During turbo boost, intake vacuum is lost, the one-way check valve leading to the intake manifold will close and a second one-way check valve leading to the suction side of the turbocharger, drawing vapor in to the turbocharger. In order for EVAP vapor canister purging to begin, following conditions must be met
- Closed loop must be active.
- No fuel adaptation in progress. This should take place for 30 seconds every 5 minutes.
- Engine coolant temperature must be more than 122°F (50°C).
- If engine coolant temperature is less than 41°F (5°C) when engine is started, vehicle speed must be more than 6 MPH. EVAP canister purge valve is noisier when it is cold. This step allow quieter operation of EVAP canister purge valve.
- Battery voltage is less than 16 volts.
- Fuel tank leak test, off.
- Engine speed is more than 770 RPM.
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.
Fuel Shutoff (Rollover) Valve
The rollover valve is in the fuel evaporation line on top of fuel tank and closes if vehicle rolls over. It also allows remaining fuel tank vapor pressure to slowly pass through it, in to the EVAP canister, after refueling.
Fuel Tank Float Valve
During refueling, vapors are pressed through float valve and into vapor canister. When tank is 95 percent 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
| CAUTION | Fuel tank non-return valve will be damaged if fuel tank is drained through filler pipe. |
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.
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 to the ECM. Return voltage fluctuates up or down from there, depending on whether fuel tank is under pressure or vacuum.
9-3 & 9-5 (2.3L Engine)
Crankcase gases are carried to external oil trap via a nipple on camshaft cover. (Scheme 1)or (Scheme 2). Gasses are then evacuated to turbo inlet pipe where they are mixed with intake air and burned in engine. A drainage hose runs from oil trap down below oil level in sump. Positive crankcase ventilation system is water heated to prevent it from icing up.
Scheme 1
Scheme 2
9-5 (3.0L Engine)
With vacuum in intake manifold, crankcase gases are sucked out via oil trap small nipple and pass through a check valve on their way to throttle body. (Scheme 3) To ensure that volume of air passing through throttle will not be excessive (and make idle speed race), small nipple in oil trap in restricted to.08" (2 mm). To prevent vacuum from becoming excessive, fresh air is admitted to oil trap through large diameter crankcase ventilation line. Fresh air comes from turbocharger intake pipe.
With pressure in intake manifold, check valve closes and prevents intake manifold air from going down into crankcase. Flow of air in large diameter line has changed direction, with result that crankcase gases pass out of oil trap large diameter connection. Crankcase gases are sucked into turbocharger intake pipe and continue through turbocharger charge air cooler into engine where accompanying hydrocarbons are burnt. Positive crankcase ventilation system is water heated to prevent it from icing up.
Scheme 3
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.
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 (9-3)
All 9-3 models have one cooling fan. Depending on market location, fan will have either 1 or 2 speeds. If vehicle is not equipped with A/C, cooling fan is controlled by engine coolant temperature only. If vehicle is equipped with A/C, cooling fan is controlled by DICE (Dashboard Integrated Control System) based on inputs from coolant temperature, A/C pressure and status (on or off), vehicle speed and ambient 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, if equipped with a 2 speed fan) for up to 3 1/2 minutes. This is due to coolant temperature information being read for 30-60 seconds after the ignition has been turned off.
Cooling Fan (9-5)
Vehicles not equipped with A/C, have one, 2-speed fan mounted behind radiator that is controlled by DICE (Dashboard Integrated Control System) based on inputs from coolant temperature.
Vehicles equipped with A/C, have two, 2-speed fans controlled by DICE based on inputs from coolant temperature, A/C pressure, vehicle speed and ambient temperature.
Cooling fan can come on up to 20 minutes after engine is turned off and can continue to run (at low speed, if equipped with a 2 speed fan) for up to 3 1/2 minutes. This is do to coolant temperature information being read for 30-60 seconds after the ignition has been turned 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. Relay(s) are controlled by DICE (Dashboard Integrated Control System) via coolant temperature signals, A/C pressure, vehicle speed and ambient 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. All relays are controlled by DICE (Dashboard Integrated Control System) via coolant temperature signals (also A/C pressure, vehicle speed and ambient temperature on A/C equipped cars) received from Trionic Engine Management System.
CRUISE CONTROL
Cruise control is operated with switch on turn signal lever. The cruise control switch has 3 outputs to ECM. When cruise control switch is in ON position, a message is sent to the ECM. ECM will than send a message, along the bus line, to the main instrument unit to turn on CRUISE light.
When the SET button is pressed, ECM will store current speed in its memory only when all conditions for setting the cruise control have been met. The ECM will then read through a table containing rolling resistance (on level ground and various speed), and set a drive wheel torque. At this point the drive wheel torque is converted to requested engine torque.
The requested engine torque is converted to requested air mass/combustion and constitutes cruise control input signal to air mass control. ECM is programmed for cruise control from factory, even if vehicle is not equipped with cruise control.