Computers and Control Systems: Description and Operation
Fuel and Emissions System Description
Electronic Control System
The functions of the fuel and emission control systems are managed by the engine control module (ECM) on vehicles with manual transmissions or the powertrain control module (PCM) on vehicles with automatic transmissions.
Self-diagnosis
The ECM/PCM detects a failure of a signal from a sensor or another control unit and stores a Temporary DTC or a DTC. Depending on the failure, a DTC is stored in either the first or the second drive cycle ('06 model: DTC P0457 turn on the malfunction indicator lamp (MIL) during the third drive cycle). When a DTC is stored, the ECM/PCM turns on the malfunction indicator lamp (MIL) by a signal sent to the gauge via F-CAN.
- One Drive Cycle Detection Method
When an abnormality occurs in the signal from a sensor or from another control unit, the ECM/PCM stores a DTC and turns on the MIL immediately.
- Two Drive Cycle Detection Method
When an abnormality occurs in the signal from a sensor or from another control unit in the first drive cycle, the ECM/PCM stores a Temporary DTC. If the failure continues in the second drive cycle, the ECM/PCM stores a DTC and turns on the MIL.
Fail-safe Function
When an abnormality occurs in the signal from a sensor or another control unit, the ECM/PCM ignores the signal and substitutes a pre-programmed value that allows the engine to continue running. This causes a DTC to be stored and the MIL to come on.
MIL Bulb Check and Readiness Code Condition
When the ignition switch is turned to ON (II), the ECM/PCM turns on the MIL via the F-CAN circuit for about 15 to 20 seconds to check the bulb condition. If any readiness codes are not set to complete, the MIL flashes five times. If all readiness codes are set to complete, the MIL goes off.
Self Shut Down (SSD) Mode
After the ignition switch is turned to LOCK (0), the ECM/PCM stays on (about 30 minutes). If the ECM/PCM connector is disconnected during this time, the ECM/PCM may be damaged. To cancel this mode, disconnect the negative cable from the battery or jump the SCS line with the HDS after the ignition switch is turned to LOCK (0).
ECM/PCM Electrical Connections
Vacuum Hose Routing
Vacuum Distribution
ECM/PCM Inputs and Outputs at Connector A (square) (44P)
NOTE: Standard battery voltage is about 12 V.
*3: USA models and Canada models with EPS
*6: Without EPS
ECM/PCM Inputs and Outputs at Connector A (square) (44P)
NOTE: Standard battery voltage is about 12 V.
*1: A/T
*5: With EPS
ECM/PCM Inputs and Outputs at Connector A (square) (44P)
NOTE: Standard battery voltage is about 12 V.
*2: M/T with cruise control
*4: With cruise control
ECM/PCM Inputs and Outputs at Connector B (triangle) (44P)
NOTE: Standard battery voltage is about 12 V.
*1: A/T
ECM/PCM Inputs and Outputs at Connector B (triangle) (44P)
NOTE: Standard battery voltage is about 12 V.
*1: A/T
ECM/PCM Inputs and Outputs at Connector B (triangle) (44P)
NOTE: Standard battery voltage is about 12 V.
*1: A/T
*3: USA models and Canada models with EPS
ECM/PCM Inputs and Outputs at Connector C (circle) (44P)
NOTE: Standard battery voltage is about 12 V.
ECM/PCM Inputs and Outputs at Connector C (circle) (44P)
NOTE: Standard battery voltage is about 12 V.
PGM-FI System
The programmed fuel injection (PGM-FI) system is a sequential multiport fuel injection system.
Air Conditioning (A/C) Compressor Clutch Relay
When the ECM/PCM receives a demand for cooling from the A/C system, it delays the compressor from being energized, and enriches the mixture to assure smooth transition to the A/C mode.
Air Fuel Ratio (A/F) Sensor
The A/F sensor operates over a wide air/fuel range. The A/F sensor is installed upstream of the TWC, and sends signals to the ECM/PCM which varies the duration of fuel injection accordingly.
Barometric Pressure (BARO) Sensor
The BARO sensor is inside the ECM/PCM. It converts atmospheric pressure into a voltage signal that modifies the basic duration of the fuel injection discharge.
Camshaft Position (CMP) Sensor
The CMP sensor detects the position of the No. 1 cylinder as a reference for sequential fuel injection to each cylinder.
Crankshaft Position (CKP) Sensor
The CKP sensor detects crankshaft speed and is used by the ECM/PCM to determine the ignition timing, timing for the fuel injection of each cylinder, and engine misfire detection.
Engine Coolant Temperature (ECT) Sensor 1 and 2
ECT sensors 1 and 2 are temperature dependent resistors (thermistors). The resistance decreases as the engine coolant temperature increases.
Ignition Timing Control
ECM/PCM contains the memory for basic ignition timing at various engine speeds and manifold absolute pressure. It also adjusts the timing according to engine coolant temperature and intake air temperature.
Injector Timing and Duration
The ECM/PCM contains the memory for basic discharge duration at various engine speeds and manifold absolute pressures. The basic discharge duration, after being read out from the memory, is further modified by signals sent from various sensors to obtain the final discharge duration.
By monitoring long term fuel trim, the ECM/PCM detects long term malfunctions in the fuel system and sets diagnostic trouble codes (DTCs) if needed.
Knock Sensor
The knock control system adjusts the ignition timing to minimize knock.
Manifold Absolute Pressure (MAP) Sensor
The MAP sensor converts manifold absolute pressure into electrical signals to the ECM/PCM.
Malfunction Indicator Lamp (MIL) Indication (In relation to Readiness Codes)
The vehicle has certain readiness codes that are part of the on-board diagnostics for the emissions systems. If the vehicle's battery has been disconnected or gone dead, if the DTCs have been cleared, or if the ECM/PCM has been reset, these codes are reset. In some states, part of the emissions testing is to make sure these codes are set to complete. If all of them are not set to complete, the vehicle may fail the test, or the test cannot be finished.
To check if the readiness codes are set to complete, turn the ignition switch to ON (II), but do not start the engine. The MIL will come on for 15-20 seconds. If it then goes off, the readiness codes are complete. If it flashes five times, one or more readiness codes are not complete. To set each code, drive the vehicle or run the engine as described in the procedures. Monitors, Trips, Drive Cycles and Readiness Codes
Mass Air Flow (MAF) Sensor/Intake Air Temperature (IAT) Sensor
The mass air flow (MAF) sensor/intake air temperature (IAT) sensor contains a hot wire sensor, a cold wire sensor, and a thermistor. It is located in the intake air passage. The resistance of the hot wire sensor, the cold wire sensor, and the thermistor changes due to intake air temperature and air flow. The control circuit in the MAF sensor controls the current to keep the hot wire at a set temperature. The current is converted to voltage in the control circuit, then output to the ECM/PCM.
Output Shaft (Countershaft) Speed Sensor
This sensor detects countershaft speed.
Secondary Heated Oxygen Sensor (Secondary HO2S)
The secondary HO2S detects the oxygen content in the exhaust gas downstream of the three way catalytic converter (TWC), and sends signals to the ECM/PCM which varies the duration of fuel injection accordingly. To stabilize its output, the sensor has an internal heater. The ECM/PCM compares the HO2S output with the A/F sensor output to determine catalyst efficiency. The secondary HO2S is on the TWC.
Electronic Throttle Control System
The throttle is electronically controlled by the electronic throttle control system. Refer to the system diagram to see a functional layout of the system.
Idle control: When the engine is idling, the ECM/PCM controls the throttle actuator to maintain the proper idle speed according to engine loads.
Acceleration control: When the accelerator pedal is pressed, the ECM/PCM opens the throttle valve, depending on the accelerator pedal position (APP) sensor signal.
Cruise control: The ECM/PCM controls the throttle actuator to maintain the set speed when the cruise control is operating. The throttle actuator takes the place of the cruise control actuator.
Accelerator Pedal Position (APP) Sensor
As the accelerator pedal position changes, the sensor varies the signal voltage to the ECM/PCM.
Throttle Body
The throttle body is a single-barrel side draft type. The lower portion of the throttle valve is heated by engine coolant from the cylinder head to prevent icing of the throttle plate.
Idle Control System
When the engine is cold, the A/C compressor is on, the transmission is in gear, the brake pedal is pressed, the power steering load is high, or the alternator is charging, the ECM/PCM sends signals to the throttle position to maintain the correct idle speed.
Brake Pedal Position Switch
The brake pedal position switch signals the ECM/PCM when the brake pedal is pressed.
Electrical Power Steering (EPS) Signal (with EPS)
The EPS signals the ECM when the power steering load is high.
Power Steering Pressure (PSP) Switch
The PSP switch signals the ECM/PCM when the power steering load is high.
Fuel Supply System
Fuel Cutoff Control
During deceleration with the throttle valve closed, current to the injectors is cut off to improve fuel economy at engine speeds over 800 rpm (A/T model), or 820 rpm (M/T model). Fuel cutoff also occurs when the engine speed exceeds 6,900 rpm, regardless of the position of the throttle valve, to protect the engine from over-revving. When the vehicle is stopped, the ECM/PCM cuts the fuel at engine speeds over 5,000 rpm (A/T model), 6,900 rpm (M/T model). On a cold engine, fuel cut occurs at a lower engine speed.
Fuel Pump Control
When the ignition switch is turned to ON (II), the ECM/PCM grounds PGM-FI main relay 2 (FUEL PUMP) which feeds current to the fuel pump for 2 seconds to pressurize the fuel system. With the engine running, the ECM/PCM grounds PGM-FI main relay 2 (FUEL PUMP) and feeds current to the fuel pump. When the engine is not running and the ignition switch is turned to ON (II), the ECM/PCM cuts ground to PGM-FI main relay 2 (FUEL PUMP) which cuts current to the fuel pump.
PGM-FI Main Relay 1 and 2
PGM-FI main relay 1 is energized whenever the ignition switch is ON (II), to supply battery voltage to the ECM/PCM, power to the injectors, and power for PGM-FI main relay 2 (FUEL PUMP). PGM-FI main relay 2 (FUEL PUMP) is energized to supply power to the fuel pump for 2 seconds when the ignition switch is turned to ON (II), and when the engine is cranking or running.
VTEC System
- This system improves fuel efficiency and reduces exhaust emissions at all levels of engine speed, vehicle speed, and engine load.
- The VTEC system changes the valve lift and timing by using more than one cam profile.
- The VTEC system changes the cam profile (angle) at cruising speeds.
(Cam angle is changed to obtain the desired EGR effect and reduce pumping loss).
Operation
At engine start and high load
- The rocker arm oil control valve is OFF.
- Oil pressure enters secondary rocker arm B from the oil passage in the intake rocker shaft.
This forces the VTEC switching piston into secondary rocker arm A and against the return spring, and disengages the secondary rocker arm A from the secondary rocker arm B to stop valve actuation.
At cruise
The rocker arm oil control valve switches oil pressure to the oil passage in the intake rocker arm shaft. Oil pressure then enters secondary rocker arm A, and it moves the VTEC switching piston in the rocker arm.
This causes the VTEC switching piston to slide into secondary rocker arm B, locking secondary rocker arms A and B together.
Catalytic Converter System
Three Way Catalytic Converter (TWC)
The TWC converts hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) in the exhaust gas to carbon dioxide (CO2), nitrogen (N2), and water vapor.
Positive Crankcase Ventilation (PCV) System
The PCV valve prevents blow-by gasses from escaping into the atmosphere by venting them into the intake manifold.
Exhaust Gas Recirculation (EGR) System
Refer to the system diagram to see a functional layout of the system.
EGR Valve
The EGR valve lowers peak combustion temperatures and reduces oxides of nitrogen emissions (NOx) by recirculating exhaust gas through the intake manifold and into the combustion chambers.
Evaporative Emission (EVAP) Control System
Refer to the system diagram to see a functional layout of the system.
EVAP Canister
The EVAP canister temporarily stores fuel vapor from the fuel tank until it can be purged from the EVAP canister into the engine and burned.
EVAP Canister Purge Valve
When the engine coolant temperature is below 140 °F (60 °C), the ECM/PCM turns off the EVAP canister purge valve cutting vacuum to the EVAP canister.
Fuel Tank Pressure (FTP) Sensor
The FTP sensor converts fuel tank absolute pressure into an electrical input to the ECM/PCM.
EVAP Canister Vent Shut Valve
The EVAP canister vent shut valve is on the EVAP canister.
The EVAP canister vent shut valve controls the venting of the EVAP canister.
Fuel Cap Warning Message
The ECM/PCM detects a loose or missing fuel fill cap as an evaporative system leak, and alerts the driver by showing a warning message in the gauge display.
First drive cycle
The first time a leak is detected, a CHECK FUEL CAP message is shown in the gauge display (A). To scroll to another message, press the select/reset button. The CHECK FUEL CAP message appears each time you restart the engine until the system turns the message off. Turn the engine off, then replace or tighten the fuel fill cap until it clicks at least once.
To make the message go off (with the HDS)
Procedure
1. Tighten the fuel fill cap until it clicks.
2. Clear the Temporary DTC with the HDS.
3. Verify there is no leak by doing the EVAP FUNCTION TEST in the INSPECTION MENU with the HDS.
To make the message go off (without the HDS) ('06 model)
Procedure
4. Tighten the fuel fill cap until it clicks.
5. The message should go off after several days of normal driving.
To make the message go off (without the HDS) ('07-09 models)
Procedure
6. Tighten the fuel fill cap until it clicks.
7. Start the engine, then turn the ignition switch to LOCK (0).
8. Repeat step 7 two more times.
Electronic Throttle Control System Diagram
The electronic throttle control system consists of the throttle actuator, throttle position (TP) sensor A/B, accelerator pedal position (APP) sensor A/B, the electronic throttle control system (ETCS) control relay, and the ECM/PCM.
Intake Manifold Tuning (IMT) Valve System
Engine power is adjusted by opening and closing the intake manifold tuning (IMT) actuator. When the valve is closed, there is high torque at low engine speed. When the valve is open, there is high torque at high engine speed.
The intake manifold tuning (IMT) valve actuator contains a sensor that detects the IMT valve position and sends it to the ECM/PCM.
Exhaust Gas Recirculation (EGR) System Diagram
The EGR system reduces oxides of nitrogen (NOx) emissions by recirculating exhaust gas through the EGR pipe and the intake manifold, and into the combustion chambers. Routing the exhaust gas through the EGR pipe helps to prevent carbon deposits from forming in the intake manifold and the throttle body. The ECM/PCM memory includes the ideal EGR valve position for varying operating conditions.
The EGR valve position sensor detects the amount of EGR valve lift and sends it to the ECM/PCM. The ECM/PCM then compares it with the ideal lift in its memory (based on signals sent from other sensors). If there is any difference between the two, the ECM/PCM cuts current to the EGR valve.
Evaporative Emission (EVAP) Control Diagram
The EVAP controls minimize the amount of fuel vapor escaping into the atmosphere. Vapor from the fuel tank is temporarily stored in the EVAP canister until it can be purged from the canister into the engine and burned.
The EVAP canister is purged by drawing fresh air through it and into a port on the intake manifold.
The purging vacuum is controlled by the EVAP canister purge valve, which operates whenever engine coolant temperature is above 140 °F (60 °C).
ECM/PCM Circuit Diagram
ECM/PCM Circuit Diagram (cont'd)
ECM/PCM Circuit Diagram (cont'd)
ECM/PCM Circuit Diagram (cont'd)
ECM/PCM Circuit Diagram (cont'd)
ECM/PCM Circuit Diagram (cont'd)
