Fuel and Emissions System Description (4D)

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.

Fail-safe Function

When an abnormality occurs in the signal from a sensor, the ECM/PCM ignores that signal and assumes a pre-programmed value for that sensor that allows the engine to continue to run.

Back-up Function

When an abnormality occurs in the ECM/PCM, the injectors are controlled by a back-up circuit independent of the system to permit minimal driving.

Self-diagnosis

When an abnormality occurs in the signal from a sensor, the ECM/PCM supplies ground for the malfunction indicator lamp (MIL) and stores the diagnostic trouble code (DTC) in erasable memory. When the ignition is first turned on, the ECM/PCM supplies ground to the MIL for 2 seconds to check the MIL bulb condition.

Two Driving Cycle Detection Method

To prevent false indications, the ‘‘two driving cycle detection method'' is used for some self-diagnostic functions. When an abnormality occurs, the ECM/PCM stores it in its memory. When the same abnormality recurs after the ignition switch is turned OFF and ON (II) again, the ECM/PCM turns on the MIL.

Self Shut Down Mode (SSD)

After the ignition switch is turned off, the ECM/PCM stays ON (up to 15 minutes).
If the ECM/PCM connector is disconnected during this mode, the ECM/PCM may be damaged.
To cancel this mode, disconnect the negative cable from the battery or jump the SCS line with the Honda PGM Tester or the HDS after the ignition switch is turned off.

ECM/PCM Inputs and Outputs at Connector A (31P)

NOTE: Standard battery voltage is 12 V.

Terminal number	Wire color	Terminal name	Description	Signal
1	RED/BLU	KS (KNOCK SENSOR)	Deyects knock sensor signal	With engine knocking: pulses
2	YEL/BLK	IGP2 (POWER SOURCE)	Power source for ECM/PCM circuit	With ignition switch ON (II): battery voltage With ignition switch OFF: about 0 V
3	YEL/BLK	IGP1 (POWER SOURCE)	Power source for ECM/PCM circuit	With ignition switch ON (II): battery voltage With ignition switch OFF: about 0 V
4	BLK	PG2 (POWER GROUND)	Ground circuit for the ECM/PCM	Less than 1.0 V at all times
5	BLK	PG1 (POWER GROUND)	Ground circuit for the ECM/PCM	Less than 1.0 V at all times
6	GRN	CMPB (CAMSHAFT POSITION SENSOR B)	Detects CMP sensor B signal	With engine running: pulses With the ignition switch ON (II): about 5 V
7	BLU	CKP (CRANKSHAFT POSITION SENSOR)	Detects CKP sensor signal	With engine running: pulses With the ignition switch ON (II): about 5 V
8	BRN/YEL	LG2 (LOGIC GROUND)	Ground circuit for the ECM/PCM	Less than 1.0 V at all times
9	BRN/YEL	LG1 (LOGIC GROUND)	Ground circuit for the ECM/PCM	Less than 1.0 V at all times
10	GRN	AFSHTC (AIR FUEL RATIO (A/F) SENSOR HEATER CONTROL)	Drives A/F sensor heater	With ignition switch ON (II): battery voltage With fully warmed up engine running: about 0 V
12^*1	BLK/RED	IACV (IDLE AIR CONTROL (IAC) VALVE)	Drives IAC valve	With engine running: duty controlled
13	BRN	IGPLS4 (No. 4 IGNITION COIL PULSE)	Drives No. 4 ignition coil	With ignition switch ON (II): about 0 V With engine running: pulses
14	WHT/BLU	IGPLS3 (No. 3 IGNITION COIL PULSE)	Drives No. 3 ignition coil
15	BLU/RED	IGPLS2 (No. 2 IGNITION COIL PULSE)	Drives No. 2 ignition coil
16	YEL/GRN	IGPLS1 (No. 1 IGNITION COIL PULSE)	Drives No. 1 ignition coil
18	BLK/BLU	NC (COUNTERSHAFT SPEED SENSOR)	Detects countershaft speed sensor signal	With ignition switch ON (II): about 0 V or about 5 V While driving: about 2.5 V
19	BLU/WHT	CMP A (CAMSHAFT POSITION SENSOR A)	Detects CMP sensor A signal	With engine running: pulses With ignition switch ON (II): about 5 V

*1:	K20A6 engine

ECM/PCM Inputs and Outputs at Connector A (31P)

NOTE: Standard battery voltage is 12 V.

Terminal number	Wire color	Terminal name	Description	Signal
20	YEL/BLU	VCC2 (SENSOR VOLTAGE)	Provides sensor voltage	With ignition switch ON (II): about 5 V With ignition switch OFF: about 0 V
21	YEL/RED	VCC1 (SENSOR VOLTAGE)	Provides sensor voltage	With ignition switch ON (II): about 5 V With ignition switch OFF: about 0 V
23	GRN/YEL	SG2 (SENSOR GROUND)	Sensor ground	Less than 1.0 V at all times
24	GRN/WHT	SG1 (SENSOR GROUND)	Sensor ground	Less than 1.0 V at all times
25^*2	RED/YEL	APSB (ACCELERATOR PEDAL POSITION (APP) SENSOR B)	Detects APP sensor B signal	With ignition switch ON (II) and accelerator pedal pressed: about 2.3 V With ignition switch ON (II) and accelerator pedal released: about 0.2 V
26^*2	RED/BLU	APSA (ACCELERATOR PEDAL POSITION (APP) SENSOR A)	Detects APP sensor A signal	With ignition switch ON (II) and accelerator pedal pressed: about 4.5 V With ignition switch ON (II) and accelerator pedal pressed: about 0.5 V
28	RED/YEL	AFS - (AIR FUEL RATIO (A/F) SENSOR, SENSOR 1 - SIDE)	Detects A/F sensor (sensor 1) signal
29^*1	RED/BLK	TPS (THROTTLE POSITION SENSOR)	Detects TP sensor signal	With throttle fully open: about 4.5 V typically With throttle fully closed: about 0.5 V
30	GRN/RED	MAP (MANIFOLD ABSOLUTE PRESSURE SENSOR)	Detects MAP sensor signal	With ignition switch ON (II): about 3V At idle: about 1.0 V (depending on engine speed)
31	RED	AFS + (AIR FUEL RATIO (A/F) SENSOR, SENSOR 1 + SIDE)	Detects A/F sensor (sensor 1) signal

*1:	K20A6 engine
*2:	K24A3 engine

ECM/PCM Inputs and Outputs at Connector B (24P)

NOTE: Standard battery voltage is 12 V.

Terminal number	Wire color	Terminal name	Description	Signal
1	BLU/WHT	VTC (VTC OIL CONTROL SOLENOID VALVE)	Drives VTC oil control solenoid valve	With ignition switch ON (II): 0 V
2	YEL	INJ4 (No. 4 INJECTOR)	Drives No. 4 injector	At idle: duty controlled With the ignition switch ON (II): battery voltage
3	BLU	INJ3 (No. 3 INJECTOR)	Drives No. 3 injector
4	RED	INJ2 (No. 2 INJECTOR)	Drives No. 2 injector
5	BRN	INJ1 (No. 1 INJECTOR)	Drives No. 1 injector
6	GRN/YEL	VTS (VTEC SOLENOID VALVE)	Drives VTEC solenoid valve	At idle: about 0 V
8	RED/WHT	ECT (ENGINE COOLANT TEMPERATURE SENSOR)	Detects ECT sensor signal	With ignition switch ON (II): about 0.1-4.8 V (depending on engine coolant temperature) With fully warmed up engine: about 0.5-0.7 V
10	WHT/BLU	ALTL (ALTERNATOR L SIGNAL)	Detects alternator signal	With ignition switch ON (II): about 0 V With engine running: battery voltage
11^*3	BLU/BLK	VTPSW (VTEC OIL PRESSURE SWITCH)	Detects VTEC oil pressure switch signal	With engine at low engine speed: about 0 V With engine at high engine speed: battery voltage
12^*1	WHT/BLK	EGRP (EXHAUST GAS RECIRCULATION (EGR) VALVE POSITION SENSOR))	Detects EGR valve position sensor signal	With engine running: 1.2 V-3.0 V (depending on EGR valve lift)
13	WHT/RED	ALTF (ALTERNATOR FR SIGNAL)	Detects alternator FR signal	With engine running: about 0 V-5 V (depending on electrical load)
15	BLU/YEL	MCS (ENGINE MOUNT CONTROL SOLENOID VALVE)	Drives engine mount control solenoid valve	At idle: about 0 V Above idle: battery voltage With ignition switch ON (II): battery voltage
16^*1	BLU/RED	EGR (EXHAUST GAS RECIRCULATION (EGR) VALVE)	Drives EGR valve	With EGR operating: duty controlled With EGR not operating: about 0 V
17	RED/YEL	IAT (INTAKE AIR TEMPERATURE SENSOR)	Detects IAT sensor signal	With ignition switch ON (II): about 0.1 V-4.8 V (depending on intake air temperture)
18	WHT/GRN	ALTC (ALTERNATOR CONTROL)	Sends alternator control signal	With engine running: and fully warmed up: about 8 V
19^*2	GRN	SEFD (THROTTLE ACTUATOR CONTROL SERIAL SIGNAL)	Sends throttle actuator control serial signal
20^*2	BLU	SEDF (THROTTLE ACTUATOR CONTROL SERIAL SIGNAL)	Detects throttle actuator control serial signal
21	YEL/BLU	PCS (EVAPORATIVE EMISSION CANISTER PURGE VALVE)	Drives EVAP canister purge valve	With engine running, engine coolant below 65°C (149°F): battery voltage With engine running, engine coolant above 65°C (149°F): duty controlled

*1:	K20A6 engine
*2:	K24A3 engine
*3:	Except KQ model

PCM Inputs and Outputs at Connector C (22P)

NOTE: Standard battery voltage is 12 V.

Terminal number	Wire color	Terminal name	Description	Signal
1^*4	RED/BLK	LSA (A/T CLUTCH PRESSURE CONTROL SOLENOID VALVE A)	Drives A/T clutch pressure control solenoid valve A	With ignition switch ON (II): duty controlled
2^*4	GRN	SHC (SHIFT SOLENOID VALVE C)	Drives shift solenoid valve C	With engine running in Neutral and [1] position, or in D or D3 position (in 1st, 3rd and 5th gears): battery voltage With engine running in Park, R position, [2], or D or D3 position (in 2nd, 4th gears): about 0 V
3^*4	YEL	SHE (SHIFT SOLENOID VALVE E)	Drives shift solenoid valve E	With engine running in Park, R position: battery voltage With engine running in Neutral position, or in D, D3, [2], and [1] position: about 0 V
4^*4	GRN/WHT	SHB (SHIFT SOLENOID VALVE B)	Drives shift solenoid valve B	With engine running in Park, R, Neutral [2], and [1] position, or D, D3 position (in 1st, 2nd gears): battery voltage With engine running in D, D3 position (in 3rd, 4th, 5th gears): about 0 V
5^*4	GRN/RED	SHD (SHIFT SOLENOID VALVE D)	Drives shift solenoid valve D	With engine running in [2] or D, D3 position (in 2nd, 5rd gears): battery voltage With engine running in Park, R, Neutral, [1] position, or D, D3 position (in 1st, 3rd, 4th, gears): about 0 V
6^*4	BLU/BLK	SHA (SHIFT SOLENOID VALVE A)	Drives shift solenoid valve A	With engine running in R and [1] position, or D, D3 position (in 1st, 4th, 5th gears): battery voltage With engine running in Park, Neutral and [2] position, or D, D3 position (in 2nd, 3rd gears): about 0 V
7^*4	BLU/YEL	LSB (A/T CLUTCH PRESSURE CONTROL SOLENOID VALVE C)	Drivers A/T clutch pressure control solenoid valve C	With the ignition switch ON (II): duty controlled
9^*4	RED	ATPD3 (TRANSMISSION RANGE SWITCH D3 POSITION)	Detects transmission range switch D3 position signal input	In D3 position: about 0 V In any other positioin: battery voltage
10^*4	BLU/WHT	OP3SW (3RD OIL PRESSURE SWITCH)	Detects 3rd oil pressure switch signal output	With ignition switch ON (II): about 5 V With 3rd clutch pressure: 0 V
12^*4	RED/WHT	ATPRVS (TRANSMISSION RANGE SWITCH R POSITION)	Detects transmission range switch R position signal input	In R position: about 0 V In any other position: battery voltage
13^*4	BLU/RED	OP2SW (2ND OIL PRESSURE SWITCH)	Detects 2nd oil pressure switch signal input	With ignition switch ON (II): about 5 V With 2nd clutch pressure: 0 V
14^*4	RED/YEL	ATFT (ATF TEMPERATURE SENSOR)	Detects ATF temperature sensor signal input	With ignition switch ON (II): about 0.2 V-4.8 V (depending on ATF temperature)

*4:

A/T

PCM Inputs and Outputs at Connector C (22P)

NOTE: Standard battery voltage is 12 V.

Terminal number	Wire color	Terminal name	Description	Signal
15^*4	BLU/WHT	LSB (A/T CLUTCH PRESSURE CONTROL SOLENOID VALVE B)	Drives A/T clutch pressure control solenoid valve B	With the ignition switch ON (II): duty controlled
17^*4	YEL/GRN	ATPD (TRANSMISSION RANGE SWITCH D POSITION)	Detects transmission range switch D position signal	In D position: about 0 V In any other position: battery voltage
18^*4	BLU/YEL	ATPFWD (TRANSMISSION RANGE SWITCH D/D3 POSITION)	Detects transmission range switch D, D3, [2] position signal	In D, D3, and [2] position: about 0 V In any other position: battery voltage
19^*4	WHT/RED	NM (MAINSHAFT SPEED SENSOR)	Detects mainshaft speed sensor signal	With ignition switch ON (II): about 0 V or about 5 V With engine running in [N] position: about 2.5 V
20^*4	RED/BLK	ATPN (TRANSMISSION RANGE SWITCH NEUTRAL POSITION)	Detects transmition range switch Neutral position signal	In Neutral position: about 0 V In any other position: battery voltage

*4:

A/T

ECM/PCM Inputs and Outputs at Connector D (17P)

NOTE: Standard battery voltage is 12 V.

Terminal number	Wire color	Terminal name	Description	Signal
2^*4	BRN	S MODE (SEQUENTIAL SPORT SHIFT MODE)	Detects sequential sportshift mode switch signal	In sequential sportshift mode (shift lever is positioned in sequential sportshift mode): 0 V In other than sequential sportshift mode: about 5 V
3^*4	WHT	SUP (UP SHIFT SWITCH)	Detects upshift switch signal	In sequential sportshift mode and shift lever pushed toward upshift position: 0 V In sequential sportshift mode and shift lever in neutral position: about 5 V
5^*4	GRN (WHT)^*7	ATPR (TRANSMISSION RANGE SWITCH R POSITION)	Detects transmission range switch R position signal	In R position: about 0 V In any other position: battery voltage
6^*4	BLU (BLU/RED)^*7	ATPP (TRANCMISSION RANGE SWITCH PARK POSITION)	Detects transmission range switch Park position signal	In Park position: about 0 V In any other position: battery voltage
8^*2	BRN	BKSWNC (BRAKE PEDAL POSITION SWITCH)	Detects brake pedal position switch signal	With ignition switch ON (II) and brake pedal released: battery voltage With ignition switch ON (II) and brake pedal pressed: about 0 V
9^*4	ORN	SDN (DOWN SHIFT SWITCH)	Detects downshift switch signal	In sequential sportshift mode and shift lever pushed toward downshift position: 0 V In sequential sportshift mode and shift lever in neutral position: about 5 V
9^*5	LT BLU	CRMTCLS (CRUISE CLUTCH PEDAL POSITION SIGNAL)	Detects cruise clutch pedal position switch signal	With ignition switch ON (II) and clutch pedal released: about 0 V With ignition switch ON (II) and clutch pedal pressed: battery voltage
10^*4	GRN	METINH (METER DISPLAY INHIBIT SIGNAL)	Send inhibit signal	With ignition switch ON (II): battery voltage
11^*4	PNK	ATCCFWD (TRANSMISSION RANGE SWITCH CRUISE CONTROL FWD SIGNAL)	Send Park and D3 transmission range switch signal to cruise control unit	In D, D3 position: about 0 V In any other than D, D3 position: battery voltage
12^*6	BLU/BLK	CCS (CRUISE CONTROL SIGNAL)	Detects cruise control signal	With cruise control: pulses
15^*2	BRN	DBWRLY (THROTTLE ACTUATOR CONTROL MODULE RELAY)	Drives throttle actuator control module relay	With ignition switch ON (II): 0 V

*2:	K24A3 engine
*4:	A/T
*5:	With cruise control (M/T)
*6:	With cruise control
*7:	RHD model

ECM/PCM Inputs and Outputs at Connector E (31P)

NOTE: Standard battery voltage is 12 V.

Terminal number	Wire color	Terminal name	Description	Signal
2^*4	GRN	SLS (SHIFT LOCK SOLENOID)	Drives shift lock solenoid	With ignition switch ON (II), in the Park position, brake pedal pressed, and accelerator released: 0 V
2^*8	GRN	RVS (REVERSE LOCK SOLENOID VALVE)	Drives reverse lock solenoid valve	With vehicle speed below 15 km/h (9.4 mph): battery voltage With vehicle speed above 20 km/h (12.5 mph): 0 V
3	BLK	LG3 (LOGIC GROUND)	Ground for ECM/PCM control circuit	Less than 1.0 V at all times
4	BLK	SG3 (SENSOR GROUND)	Sensor ground	Less than 1.0 V at all times
7	RED/BLK	MRLY (PGM-FI MAIN RELAY)	Drives PGM-FI main relay 1 (FI MAIN) Power source for DTC memory	With ignition switch ON (II): about 0 V With ignition switch OFF: battery voltage
8	ORN	AFSHTCR (AIR FUEL RATIO (A/F) SENSOR HEATER CONTROL RELAY)	Drives A/F sensor heater relay	With ignition switch ON (II): 0 V
9	BLK/YEL	IG1 (IGNITION SIGNAL)	Detects ignition signal	With ignition switch ON (II): battery voltage With ignition switch OFF: about 0 V
11	WHT	CAN H (CAN COMMUNICATION SIGNAL HIGH)	Sends communication signal	With ignition switch ON (II): pulses
12	GRN	FANC (RADIATOR FAN CONTROL)	Drives radiator fan relay	With radiator fan running: about 0 V With radiator fan stopped: battery voltage
15	BLU	ELD (ELECTRICAL LOAD DETECTOR)	Detects ELD signal	With ignition switch ON (II): about 0.1 V-4.8 V (depending on electrical load)
16	GRY	PSPSW (POWER STEERING PRESSURE SWITCH SIGNAL)	Detects PSP switch signal	At idle with steering wheel straight ahead: 0 V At idle with steering wheel at full lock: battery voltage
16^*9	GRY	EPSLD (ELECTRICAL POWER STEERING LOAD DETECT)	Detects power steering load signal	At idle with steering wheel in straight ahead position: about 0 V At idle with steering wheel at full lock: battery voltage momentarily
17	WHT	IMO FPR (IMMOBILIZER FUEL PUMP RELAY)	Drives PGM-FI main relay 2 (FUEL PUMP)	0 V for 2 seconds after turning ignition switch ON (II), then battery voltage
18	BRN	ACC (A/C CLUTCH RELAY)	Drives A/C clutch relay	With compressor ON: about 0 V With compressor OFF: battery voltage
20	WHT/RED	SHO2S (SECONDARY HEATED OXYGEN SENSOR (SECONDAY HO2S), SENSOR 2)	Detects secondary HO2S (sensor 2) signal	With throttle fully closed and idle with fully warmed up engine: above 0.6 V With throttle quickly closed: below 0.4 V
21	BLK/WHT (LT GRN)^*7	SHO2SHTC (SECONDARY HEATED OXYGEN SENSOR (SECONDAY HO2S) HEATER CONTROL)	Drives secondary HO2S heater	With ignition switch ON (II): battery voltage With fully warmed up engine running: duty controlled

*7:	RHD model
*8:	M/T
*9:	with EPS model

ECM/PCM Inputs and Outputs at Connector E (31P)

NOTE: Standard battery voltage is 12 V.

Terminal number	Wire color	Terminal name	Description	Signal
22	WHT/BLK	BKSW (BRAKE PEDAL POSITION SWITCH)	Detects brake pedal position switch signal	With brake pedal released: about 0 V With brake pedal pressed: battery voltage
23	LT BLU	K-LINE	Sends and receives scan tool signals	With ignition switch ON (II): pulses or battery voltage
24	RED	CANL (CAN COMMUNICATION SIGNAL LOW)	Sends the communication signal	With ignition switch ON (II): pulses
25	WHT	NEP(ENGINE SPEED PULSE)	Outputs engine speed pulse	With engine running: pulses
26	BLU	VSSOUT (VEHICLE SPEED SENSOR OUTPUT SIGNAL)	Sends vehicle speed sensor signal	Depending on vehicle speed: pulses With ignition switch ON (II): battery voltage
27	RED	IMOCD (IMMOBILIZER CODE)	Detects immobilizer signal
29	BRN	SCS (SERVICE CHECK SIGNAL)	Detects service check signal	With the service check signal shorted using PGM Tester or HDS: about 0 V With the service check signal open: about 5 V
30	RED (RED/WHT)^*7	WEN (WRITE ENABLE SIGNAL)	Detects write enable signal	With ignition switch ON (II): about 0 V

*7:

RHD model

Vacuum Hose Routing

Vacuum Distribution

K24A3 engine:

K20A6 engine:

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 B

The CMP sensor B detects the position of the No. 1 cylinder as a reference for sequential fuel injection to each cylinder.

Countershaft Speed Sensor

This sensor detects countershaft speed.

Crankshaft Position (CKP) Sensor

The CKP sensor detects crankshaft speed and determines ignition timing and timing for fuel injection of each cylinder as well as detecting engine misfire.

Engine Coolant Temperature (ECT) Sensor

The ECT sensor is a temperature dependent resistor (thermistor). The resistance of the thermistor decreases as the engine coolant temperature increases.

Ignition Timing Control

The 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 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 a diagnostic trouble code (DTC).

Intake Air Temperature (IAT) Sensor

The IAT sensor is a temperature dependent resistor (thermistor). The resistance of the thermistor decreases as the intake air temperature increases.

Knock Sensor

The knock control system adjusts the ignition timing to minimize knock.

Malfunction Indicator Lamp (MIL) Indication

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.

Manifold Absolute Pressure (MAP) Sensor

The MAP sensor converts manifold absolute pressure into electrical signals to the ECM/PCM.

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 located on the TWC.

Throttle Position (TP) Sensor (K20A6 engine)

The TP sensor is a potentiometer connected to the throttle valve shaft. As the throttle position changes, the sensor varies the signal voltage to the ECM/PCM. The TP sensor is not replaceable apart from the throttle body.

Electronic Throttle Control System (K24A3 engine)

The throttle is electronically controlled by the electronic throttle control system. Refer to the System Diagram to see the 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 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.

VTEC/VTC

The i-VTEC has a VTC (Variable Valve Timing Control) mechanism on the intake camshaft in addition to the usual VTEC.
This mechanism improves fuel efficiency and reduces exhaust emissions at all levels of engine speed, vehicle speed, and engine load.
The VTEC mechanism changes the valve lift and timing by using more than one cam profile.
The VTC changes the phase of the intake camshaft via oil pressure. It changes the intake valve timing continuously.

Driving Condition	VTC Control	Description
(1) Light-load	Base Position	Cam angle is retarded to reduce the entry of exhaust gas into the intake port.
(2) Medium/high-load	Advance Control	To reduce pumping loss, the intake valve is closed quickly to help reduce the entry of air/fuel mixture into the intake port and improve the charging effect.
(3) High speed	Advance-Base Position	Cam phase angle is controlled for optimum valve timing and maximum engine power.

VTC system

The VTC system makes continuous intake valve timing changes based on operating conditions.
Intake valve timing is optimized to allow the engine to produce maximum power.
Cam angle is advanced to obtain the EGR effect and reduce pumping loss. The intake valve is closed quickly to reduce the entry of the air/fuel mixture into the intake port and improve the charging effect.
The system reduces the cam advance at idle, stabilizes combustion, and reduces engine speed.
If a malfunction occurs, the VTC system control is disabled and the valve timing is fixed at the fully retarded position.

VTEC system

The VTEC system changes the cam profile to correspond to the engine speed. It maximizes torque at low engine speed and output at high engine speed.
The low lift cam is used at low engine speeds, and the high lift cam is used at high engine speeds.

VTEC/VTC

System Diagram

Camshaft Position (CMP) Sensor A

This sensor detects camshaft angle position for the VTC system.

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 controls current to the idle air control (IAC) valve to maintain the correct idle speed. Refer to the System Diagram to see the functional layout of the system.

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 control)

The EPS signals the ECM/PCM when the power steering load is high.

Idle Air Control (IAC) Valve (K20A6 engine)

To maintain proper idle speed, the IAC valve changes the amount of air bypassing the throttle body in response to an electrical signal from the ECM/PCM.

Power Steering Pressure (PSP) Switch (without EPS control)

The PSP switch signals the ECM/PCM when the power steering load is high.

Fuel Supply System

Fuel Cut-off Control

During deceleration with the throttle valve closed, current to the injectors is cut off to improve fuel economy at engine speeds over 1,000 rpm (min^-1)
(M/T: 1,000 rpm (min^-1)). Fuel cut-off control also occurs when the engine speed exceeds 7,300 rpm (min^-1)
(K20A6 engine: 6,900 rpm (min^-1)), 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 (min^-1) (M/T: 4,500 rpm (min^-1)).

Fuel Pump Control

When the ignition is turned on, the ECM/PCM grounds the PGM-FI main relay which feeds current to the fuel pump for 2 seconds to pressurize the fuel system. With the engine running, the ECM/PCM grounds the PGM-FI main relay and feeds current to the fuel pump. When the engine is not running and the ignition is on, the ECM/PCM cuts ground to the PGM-FI main relay which cuts current to the fuel pump.

PGM-FI Main Relay 1 and 2

The PGM-FI relay consists of two separate relays. PGM-FI main relay 1 (FI MAIN) 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 is energized to supply power to the fuel pump for 2 seconds when the ignition switch is turned ON (II), and when the engine is cranking or running.

Intake Air System

Refer to the System Diagram to see the functional layout of the system.

Intake Air Bypass Control Thermal Valve (with TWC model)

When the engine is running, the intake air bypass control thermal valve sends air to the injector.
The amount of air is regulated by engine coolant temperature.

Throttle Body (K20A3 engine)

The throttle body is a single-barrel side draft type. The lower portion of the idle air control (IAC) valve is heated by engine coolant from the cylinder head to prevent icing of the throttle plate.

Catalytic Converter System (with TWC model)

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.

Evaporative Emission (EVAP) Control System

Refer to the System Diagram to see the 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 65°C (149°F), the ECM/PCM turns off the EVAP canister purge valve which cuts vacuum to the EVAP canister.

Idle Control System Diagram

The idle speed of the engine is controlled by the idle air control (IAC) valve:

After the engine starts, the IAC valve opens for a certain amount of time. The amount of air is increased to raise the idle speed.
When the engine coolant temperature is low, the IAC valve is opened to obtain the proper fast idle speed. The amount of bypassed air is controlled in relation to engine coolant temperature.

Intake Air System Diagram

This system supplies air for engine needs. A resonator in the intake air duct provides additional silencing as air is drawn into the system.

Electronic Throttle Control System Diagram

The electronic throttle control system consists of the throttle actuator, throttle position (TP) sensor, accelator pedal position (APP) sensor, throttle actuator control module, and the ECM/PCM. The throttle is electronically controlled by this system.

Exhaust Gas Recirculation (EGR) System Diagram

The EGR system reduces oxides of nitrogen (NOx) emissions by recirculating exhaust gas through the EGR valve and the intake manifold into the combustion chambers. 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 to 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 65°C (149°F).

ECM/PCM Circuit Diagram

ECM/PCM Circuit Diagram (cont'd)

NOTE:

Connector with male terminals (double outline): view from terminal side
Connector with female terminals (single outline): view from wire side

ECM/PCM Circuit Diagram (cont'd)

LHD model:

ECM/PCM Circuit Diagram (cont'd)

LHD model:

ECM/PCM Circuit Diagram (cont'd)

LHD model:

ECM/PCM Circuit Diagram (cont'd)

RHD model:

ECM/PCM Circuit Diagram (cont'd)

RHD model:

ECM/PCM Circuit Diagram (cont'd)

RHD model: