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 a 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 for 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 informs the driver by turning on the MIL.

ECM/PCM Data


You can retrieve data from the ECM/PCM by connecting the scan tool or the Honda PGM Tester to the Data Link Connector (DLC). The items listed in the table below conform to SAE recommended practice. The Honda PGM Tester also reads data beyond that recommended by SAE so that this data may help you find the causes of intermittent problems.

NOTE:

Data Description Operating Value Freeze Data 
Diagnostic Trouble Code (DTC) If the ECM/PCM detects a problem, it will store it as a code consisting of one letter and four numbers. Depending on the problem, an SAE-defined code (P0xxx) or a Honda-defined code (P1xxx) will be output to the tester. If no problem is detected, there is no output. YES 
Engine Speed The ECM/PCM computes engine speed from the signals sent from the Crankshaft Position (CKP) sensor. This data is used for determining the time and amount of injected fuel. Nearly the same as tachometer indication
At idle speed: 650±50 rpm (min-1
YES 
Vehicle Speed The ECM/PCM converts pulse signals from the Vehicle Speed Sensor (VSS). Nearly the same as speedometer indication YES 
Manifold Absolute Pressure (MAP) The absolute pressure caused in the intake manifold by engine load and speed. With engine stopped: Nearly the same as atmospheric pressure
At idle speed: about 20-34 kPa (150-260 mmHg, 6-10 in.Hg), 0.7-1.1 V 
YES 
Engine Coolant Temperature (ECT) The ECT sensor converts coolant temperature into voltage and signals the ECM/PCM. The sensor is a thermistor whose internal resistance changes with coolant temperature. The ECM/PCM uses the voltage signals from the ECT sensor to determine the amount of injected fuel. With cold engine: Same as ambient temperature and IAT
With engine warmed up: about 80-100°C (176-212°F), 0.5-0.8 V 
YES 
Heated Oxygen Sensor ( HO2S), Secondary Heated Oxygen Sensor (Secondary HO2S) (Sensor 2) The HO2S detects the oxygen content in the exhaust gas and sends voltage signals to the ECM/PCM. Based on these signals, the ECM/PCM controls the air fuel ratio. When the oxygen content is high (that is, when the ratio is leaner than the stoichiometric ratio), the voltage signal is lower. When the oxygen content is low (that is, when the radio is richer than the stoichiometric ratio), the voltage signal is higher. 0.0-1.25 V
At idle speed:
about 0.1-0.9 V 
NO 

ECM/PCM Data (cont'd)


Data Description Operating Value Freeze Data 
Fuel System Status Fuel system status is indicated as ''open'' or ''closed''.
Closed: Based on the HO2S output, the ECM/PCM determines the air/fuel ratio and controls the amount of injected fuel.
Open: ignoring the HO2S output, the ECM/PCM refers to signals from the Throttle Position (TP), Manifold Absolute Pressure (MAP), Intake Air Temperature (IAT), Barometric Pressure (BARO) and Engine Coolant Temperature (ECT) sensors to control the amount of injected fuel. 
At idle speed: closed YES 
Short Term Fuel Trim The air/fuel ratio correction coefficient for correcting the amount of injected fuel when the Fuel System Status is ''closed.'' When the ratio is leaner than the stoichiometric ratio, the ECM/PCM increases short term fuel trim gradually, and the amount of injected fuel increases. The air/fuel ratio gradually gets richer, causing a lower oxygen content in the exhaust gas. Consequently, the short term fuel trim is lowered, and the ECM/PCM reduces the amount of injected fuel.
This cycle keeps the air/fuel ratio close to the stoichiometric ratio when in closed loop status. 
0.73-1.47 YES 
Long Term Fuel Trim Long term fuel trim is computed from short term fuel trim and indicates changes occurring in the fuel supply system over a long period.
If long term fuel trim is higher than 1.00, the amount of injected fuel must be increased. If it is lower than 1.00, the amount of injected fuel must be reduced. 
0.82-1.47 YES 
Intake Air Temperature (IAT) The IAT sensor converts intake air temperature into voltage and signals the ECM/PCM. When intake air temperature is low, the internal resistance of the sensor increases, and the voltage signal is higher. With cold engine:
Same as ambient temperature and ECT 
YES 
Throttle Position Based on the accelerator pedal position, the opening angle of the throttle valve is indicated. At idle speed:
about 10 %, 0.5 V 
YES 
Ignition Timing Ignition timing is the ignition advance angle set by the ECM/PCM. The ECM/PCM matches ignition timing to the driving conditions. At idle speed: 8° ± 2°
BTDC when the SCS service signal line is jumped with the Honda PGM tester 
NO 

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*3 BLK/WHT PO2SHTC (PRIMARY HEATED OXYGEN SENSOR HEATER CONTROL) Drives Primary HO2S heater With ignition switch ON (II): battery voltage
With fully warmed up engine running: duty controlled 
YEL/BLK IGP2 (POWER SOURCE) Power source for the ECM/PCM circuit With the ignition switch ON (II): battery voltage
With the ignition switch OFF: about 0 V 
YEL/BLK IGP1 (POWER SOURCE) Power source for the ECM/PCM circuit With the ignition switch ON (II): battery voltage
With the ignition switch OFF: about 0 V 
BLK PG2 (POWER GROUND) Ground for the ECM/PCM circuit Less than 1.0 V at all times 
BLK PG1 (POWER GROUND) Ground for the ECM/PCM circuit Less than 1.0 V at all times 
   6*3 RED PHO2S (PRIMARY HEATED OXYGEN SENSOR, Sensor 1) Detects Primary HO2S sensor (Sensor 1) signal With throttle fully opened from idle with fully warmed up engine: about 0.6 V
With throttle quickly closed: below 0.4 V 
BLU CKP (CRANKSHAFT POSITION SENSOR) Detects CKP sensor signal With engine running: pulses 
RED/BLU KS (KNOCK SENSOR) Detects knock sensor signal With ignition ON (II): about 0 V
With engine knocking: pulses 
10 GRN/YEL SG2 (SENSOR GROUND) Sensor ground Less than 1.0 V at all times 
11 GRN/WHT SG1 (SENSOR GROUND) Sensor ground Less than 1.0 V at all times 
12 BLK/RED IACV (IDLE AIR CONTROL (IAC) VALVE) Drives IAC valve With engine running: duty controlled 
15 RED/BLK TPS (THROTTLE POSITION SENSOR) Detects TP sensor signal With throttle fully open: about 4.8 V
With throttle fully closed: about 0.5 V 
   18*2 WHT/GRN VSS (VEHICLE SPEED SENSOR) Detects VSS signal With ignition switch ON (II) and front wheels rotating: cycles about 0 V-about 5 V or battery voltage 
19 GRN/RED MAP (MANIFOLD ABSOLUTE PRESSURE SENSOR) Detects MAP sensor signal With ignition switch ON (II): about 3 V
At idle: about 1.0 V (depending on engine speed) 
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 BRN/YEL LG2 (LOGIC GROUND) Ground for the ECM/PCM circuit Less than 1.0 V at all times 
24 BRN/YEL LG1 (LOGIC GROUND) Ground for the ECM/PCM circuit Less than 1.0 V at all times 
25 BLU/WHT CMP (CAMSHAFT POSITION SENSOR) Detects CMP sensor signal With engine running: pulses 
26 GRN TDC (TOP DEAD CENTER SENSOR) Detects TDC sensor With engine running: pulses 
27 BRN IGPLS4 (No.4 IGNITION COIL PULSE) Drives No.4 ignition coil With ignition switch ON (II): about 0 V
With engine running: pulses 
28 WHT/BLU IGPLS3 (No.3 IGNITION COIL PULSE) Drives No.3 ignition coil 
29 BLU/RED IGPLS2 (No.2 IGNITION COIL PULSE) Drives No.2 ignition coil 
30 YEL/GRN IGPLS1 (No.1 IGNITION COIL PULSE) Drives No.1 ignition coil 
*1: A/T
*2: M/T
*3: with TWC model
*4: KG, KS, KE, KR, KU, KZ, FO, KQ, KK, KM models
*5: KG, KS, KE, KR, KU (Hong Kong) models
*6: KG, KS, KE, KR, KU, KZ, FO, KQ models
*7: KG, KS, KE, KR, KU, KN, KH, KY, KZ, FO, KQ, KK, KM models
*8: except KG, KS, KE, KR, KU, KN, KH, KY, KZ, FO, KQ, KK, KM models
*9: except TWC model
*10: with cruise control

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

 

NOTE: Standard battery voltage is 12 V.

Terminal number Wire color Terminal name Description Signal 
BLU/WHT VTC+ (VTC OIL CONTROL SOLENOID VALVE +SIDE) Drives VTC oil control solenoid valve With ignition switch ON (II): 0 V 
YEL INJ4 (No. 4 INJECTOR) Drives No. 4 injector At idle: duty controlled
With ignition switch ON (II): battery voltage 
BLU INJ3 (No. 3 INJECTOR) Drives No. 3 injector 
RED INJ2 (No. 2 INJECTOR) Drives No. 2 injector 
BRN INJ1 (No. 1 INJECTOR) Drives No. 1 injector 
GRN FANC (RADIATOR FAN CONTROL) Drives radiator fan relay With radiator fan running: about 0 V
With radiator fan stopped: battery voltage 
RED/WHT ECT (ENGINE COOLANT TEMPERATURE SENSOR) Detects ECT sensor signal With the ignition switch ON (II): about 0.1-4.8 V
(depending on engine coolant temperature) 
   9*5 BLU/BLK VTPSW (VTEC OIL PRESSURE SWITCH) Detects VTEC oil pressure switch signal At idle: about 0 V 
10 WHT/BLU ALTL (ALTERNATOR L SIGNAL) Detects alternator L signal With ignition switch ON (II): about 0 V
With engine running: battery voltage 
13 WHT/RED ALTF (ALTERNATOR FR SIGNAL) Detects alternator FR signal With engine running:about 0 V-5 V
(depending on electrical load) 
   14*1 RED/BLK LSA+ (A/T PRESSURE CONTROL SOLENOID VALVE A +SIDE) Drives A/T pressure control solenoid valve A With the ignition switch ON (II): duty controlled 
15 GRN/YEL VTS (VTEC SOLENOID VALVE) Drives VTEC solenoid valve At idle: about 0 V 
   16*1 BRN/WHT LSB+ (A/T PRESSURE CONTROL SOLENOID VALVE B +SIDE) Drives A/T pressure control solenoid valve B With the ignition switch ON (II): duty controlled 
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 temperature) 
   18*4 WHT/GRN ALTC (ALTERNATOR CONTROL) Sends alternator control signal With engine running: about 0 V-5 V
(depending on electrical load) 
21 YEL/BLU PCS (EVAPORATIVE EMISSION CANISTER PURGE VALVE) Drives EVAP canister purge valve With engine running, engine coolant below 65°C (149°F): about 0 V
With engine running, engine coolant above 65°C (149°F): duty controlled 
22 RED/BLU IMRC (INTAKE MANIFOLD RUNNER CONTROL SOLENOID VALVE) Drives IMRC solenoid valve With engine speed below 4,700 rpm (min-1) (K24A1 engine: 4,300 rpm (min-1)): battery voltage
With engine speed above 4,700 rpm (min-1) (K24A1 engine: 4,300 rpm (min-1)): 0 V 
23 BLK/WHT VTC- (VTC OIL CONTROL SOLENOID VALVE -SIDE) Drives VTC oil control solenoid valve With the ignition switch ON (II): 0 V 
   24*1 BLU/YEL LSC+ (A/T PRESSURE CONTROL SOLENOID VALVE C +SIDE) Drives A/T pressure control solenoid valve C With the ignition switch ON (II): duty controlled 
*1: A/T
*2: M/T
*3: with TWC model
*4: KG, KS, KE, KR, KU, KZ, FO, KQ, KK, KM models
*5: KG, KS, KE, KR, KU (Hong Kong) models
*6: KG, KS, KE, KR, KU, KZ, FO, KQ models
*7: KG, KS, KE, KR, KU, KN, KH, KY, KZ, FO, KQ, KK, KM models
*8: except KG, KS, KE, KR, KU, KN, KH, KY, KZ, FO, KQ, KK, KM models
*9: except TWC model
*10: with cruise control

PCM Inputs and Outputs at Connector C (22P)*1

 

NOTE: Standard battery voltage is 12 V.

Terminal number Wire color Terminal name Description Signal 
WHT/BLK LSA- (A/T PRESSURE CONTROL SOLENOID VALVE A -SIDE) Ground for A/T pressure control solenoid valve A  
GRN SHC (SHIFT SOLENOID VALVE C) Drives shift solenoid valve C With engine running in Neutral position, or in D, M position (in 1st, 3rd, 5th gears): battery voltage
With engine running in Park, R position, or in D, M position (in 2nd, 4th gears): about 0 V 
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, M position (in 1st, 2nd, 3rd, 4th, 5th gears): about 0 V 
GRN/WHT SHB (SHIFT SOLENOID VALVE B) Drives shift solenoid valve B With engine running in Park, R, Neutral position, or D, M position (in 1st, 2nd gears): battery voltage
With engine running in D, M position (in 3rd, 4th, 5th gears): about 0 V 
BLU/BLK SHA (SHIFT SOLENOID VALVE A) Drives shift solenoid valve A With engine running in R position, or D, M position (in 1st, 4th, 5th gears): battery voltage
With engine running in Park, Neutral position, or D, M position (in 2nd, 3rd gears): about 0V 
WHT/RED NM (MAINSHAFT SPEED SENSOR) Detects mainshaft speed sensor signals With engine running: pulses 
BLK/RED LSB- (A/T PRESSURE CONTROL SOLENOID VALVE B -SIDE) Ground for A/T pressure control solenoid valve B  
10 BLU/WHT OP3SW (3RD OIL PRESSURE SWITCH) Detects 3rd oi pressure switch With the ignition switch ON (II): about 5 V
With engine running in 3rd gear: about 0 V 
11 GRN/RED ATP2 (TRANSMISSION RANGE SWITCH 2ND POSITION) Detects transmission range switch 2nd position signal In 2nd position: about 0 V
In any other position: battery voltage 
12 RED/WHT ATPRVS (TRANSMISSION RANGE SWITCH R POSITION) Detects transmission range switch R position signal In R position: about 0 V
In any other position: about 5 V or battery voltage 
13 BLU/RED OP2SW (2ND OIL PRESSURE SWITCH) Detects 2nd oil pressure switch With the ignition switch ON (II): about 5 V
With engine running in 2nd gear: about 0 V 
14 RED/YEL ATFT (ATF TEMPERATURE SENSOR) Detects ATF temperature sensor signal With the ignition switch ON (II): about 0.1 V-4.2 V
(depending on ATF temperature) 
15 BLU NC (COUNTERSHAFT SPEED SENSOR) Detects countershaft speed sensor signals With ignition switch ON (II), and front wheels rotating: pulses 
16 WHT/BLU LSC- (A/T PRESSURE CONTROL SOLENOID VALVE C -SIDE) Ground for A/T pressure control solenoid valve C With the ignition switch ON (II): duty controlled 
19 BRN ATP1 (TRANSMISSION RANGE SWITCH 1ST POSITION) Detects transmission range switch 1st position signal In 1st position: about 0 V
In any other position: battery voltage 
*1: A/T
*2: M/T
*3: with TWC model
*4: KG, KS, KE, KR, KU, KZ, FO, KQ, KK, KM models
*5: KG, KS, KE, KR, KU (Hong Kong) models
*6: KG, KS, KE, KR, KU, KZ, FO, KQ models
*7: KG, KS, KE, KR, KU, KN, KH, KY, KZ, FO, KQ, KK, KM models
*8: except KG, KS, KE, KR, KU, KN, KH, KY, KZ, FO, KQ, KK, KM models
*9: except TWC model
*10: with cruise control

PCM Inputs and Outputs at Connector D (17P)

 

NOTE: Standard battery voltage is 12 V.

Terminal number Wire color Terminal name Description Signal 
GRN ODSW (OVER-DRIVE SWEITCH) Detects over-drive switch signal With Over-Drive OFF (O/D OFF indicator light turned ON): about 0 V
With Over-Drive ON (O/D OFF indicator light turned OFF): about 5 V 
BLK/RED ATPN (TRANSMISSION RANGE SWITCH NEUTRAL POSITION) Detects transmission range switch Neutral position signal In Neutral position: about 0 V
In any other position: about 5 V or battery voltage 
WHT ATPR (TRANSMISSION RANGE SWITCH R POSITION) Detects transmission range switch R position signal In R position: about 0 V
In any other position: about 5 V or battery voltage 
BLU/BLK ATPP (TRANSMISSION RANGE SWITCH PARK POSITION) Detects transmission range switch Park position signal In Park position: about 0 V
In any other position: about 5 V or battery voltage 
10 LT BLU ATPD (TRANSMISSION RANGE SWITCH D POSITION) Detects transmission range switch D position signal In D position: about 0 V
In any other position: about 5 V or battery voltage 
   12*10 BLU/ORN CCS (CRUISE CONTROL SIGNAL) Detects cruise control signal With ignition switch ON (II): pulses 
*1: A/T
*2: M/T
*3: with TWC model
*4: KG, KS, KE, KR, KU, KZ, FO, KQ, KK, KM models
*5: KG, KS, KE, KR, KU (Hong Kong) models
*6: KG, KS, KE, KR, KU, KZ, FO, KQ models
*7: KG, KS, KE, KR, KU, KN, KH, KY, KZ, FO, KQ, KK, KM models
*8: except KG, KS, KE, KR, KU, KN, KH, KY, KZ, FO, KQ, KK, KM models
*9: except TWC model
*10: with cruise control

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

 

NOTE: Standard battery voltage is 12 V.

Terminal number Wire color Terminal name Description Signal 
   1*7 GRN/YEL IMO FPR (IMMOBILIZER FUEL PUMP RELAY) Drives PGM-FI main ralay 2 0 V for 2 seconds after turning ignition switch ON (II), then battery voltage 
   2*6 WHT/RED SHO2S (SECONDARY HEATED OXYGEN SENSOR, SENSOR 2) Detects Secondary HO2S (sensor 2) signal With throttle fully opened from idle with fully warmed up engine: above 0.6 V
With throttle quickly closed: below 0.4 V 
BRN/YEL LG3 (LOGIC GROUND) Ground for the ECM/PCM control circuit Less than 1.0 V at all times 
PNK SG3 (SENSOR GROUND) Sensor ground Less than 1.0 V at all times 
YEL/BLU VCC3 (SENSOR VOLTAGE) Provides sensor voltage With ignition switch ON (II): about 5 V
With ignition switch OFF: about 0 V 
   6*6 BLK/WHT SO2SHTC (SECONDARY HEATED OXYGEN SENSOR HEATER CONTROL) Drives Secondary HO2S heater With ignition switch ON (II): battery voltage
With fully warmed up engine running: duty controlled 
RED/YEL MRLY (PGM-FI MAIN RELAY) Drives PGM-FI main relay 1
Power source for the DTC memory 
With ignition switch ON (II): battery voltage
With ignition switch OFF: about 0 V 
YEL/BLK IG1 (IGNITION SIGNAL) Detects ignition signal With ignition switch ON (II): battery voltage
With ignition switch OFF: about 0 V 
   10*8 GRN/YEL FPR (FUEL PUMP RELAY) Drives PGM-FI main relay 2 0 V for 2 seconds after turning ignition switch ON (II), then battery voltage 
   13*1 WHT/BLU ILU (INTERLOCK CONTROL UNIT) Drives interlock control unit With ignition switch ON (II) and brake pedal depressed: about 8.5 V 
   15*4 GRN/RED ELD (ELECTRICAL LOAD DETECTOR) Drives ELD signal With ignition switch ON (II): about 0.1 V-4.8 V
(depending on electrical load) 
   15*9 ORN IMA (IDLE MIXTURE ADJUSTER (IMA)) Detects IMA signal With ignition switch ON (II): about 0.5-4.5 V (depending on idle mixture) 
16 LT GRN/BLK PSPSW (POWER STEERING PRESSURE SWITCH SIGNAL) Detects PSP switch signal At idle steering wheel in straight ahead position: about 0 V
At idle with steering wheel at full lock: battery voltage 
18 RED ACC (A/C CLUTCH RELAY) Drives A/C clutch relay With compressor ON: about 0 V
With compressor OFF: battery voltage 
22 WHT/BLK BKSW (BRAKE PEDAL POSITION SWITCH) Detects BPP 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 signal With ignition switch ON (II): pulses or battery voltage 
24 YEL SEFMJ Communicates with multiplex control unit With ignition switch ON (II): about 5 V
With engine running with load: pulses 
   25*1 BLU/WHT VSSOUT (VEHICLE SPEED SENSOR OUTPUT SIGNAL) Sends vehicle speed sensor signal Depending on vehicle speed: pulses 
26 BLU NEP (ENGINE SPEED PULSE) Outputs engine speed pulse With engine running: pulses 
   27*7 RED/BLU IMOCD (IMMOBILIZER CODE) Detects immobilizer signal  
29 BRN SCS (SERVICE CHECK SIGNAL) Detects service check signal With the service check signal shorted with the PGM Tester: about 0 V
With the service check signal opened: about 5 V battery voltage 
31 GRN/WHT MIL (MALFUNCTION INDICATOR LAMP) Drives MIL With MIL turned ON: about 0 V
With MIL turned OFF: battery voltage 

*1: A/T *6: KG, KS, KE, KR, KU, KZ, FO, KQ models 
*2: M/T *7: KG, KS, KE, KR, KU, KN, KH, KY, KZ, FO, KQ, KK, KM models 
*3: with TWC model *8: except KG, KS, KE, KR, KU, KN, KH, KY, KZ, FO, KQ, KK, KM models 
*4: KG, KS, KE, KR, KU, KZ, FO, KQ, KK, KM models *9: except TWC model 
*5: KG, KS, KE, KR, KU (Hong Kong) models *10: with cruise control 

Vacuum Hose Routing


 

Vacuum Distribution


 

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.

Alternator Control

The alternator signals the Engine Control Module (ECM)/ Powertrain Control Module (PCM) during charging.

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.

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 resistor of the thermistor decreases as the engine coolant temperature increases.

 

Idle Mixture Adjuster (IMA) (without TWA model)

The idle mixture adjuster (IMA) is selected resistance device used to control idle mixture.

 

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.

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 will set 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.

 


Manifold Absolute Pressure (MAP) Sensor

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

 

Primary Heated Oxygen Sensor (Primary HO2S)

The primary HO2S detects the oxygen content in the exhaust gas 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 primary HO2S is installed in the Three Way Catalytic Converter (TWC). By controlling the air fuel ratio with primary HO2S and secondary HO2S, the deterioration of the primary HO2S can be evaluated by its feedback period. When the feedback period exceeds a certain value during stable driving conditions, the sensor is considered deteriorated and the ECM/PCM sets a DTC.

 

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 secondary HO2S is installed in the TWC.

 

Starting Control

When the engine is started, the ECM/PCM provides a rich mixture by increasing injector duration.

Throttle Position (TP) Sensor

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.

 

Top Dead Center (TDC) Sensor

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

 

Vehicle Speed Sensor (VSS)

The VSS is driven by the differential. It generates a pulsed signal from an input of 5 volts. The number of pulses per minute increases/decreases with the speed of the vehicle.

VTEC/VTC


 

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 and to achieve stable fuel consumption during lean burn. 
(2) medium/high-load Advance Control Cam angle is advanced for EGR effect and to reduce this 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. 

VTEC/VTC


VTC system

 

VTEC system

 

System Diagram

 

Camshaft Position (CMP) Sensor

The CMP 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.

Idle Air Control (IAC) Valve

To maintain the 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

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 speeds over 850 rpm (min-1) (KY, KH, PH, KP, IN models: 900 rpm (min-1)). Fuel cut-off action also occurs when engine speed exceeds 6,900 rpm (min-1) (K24A1 engine: 6,700 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 6,500 rpm (min-1) (A/T: 5,000 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 is energized whenever the ignition switch is ON (II) which supplies battery voltage to the ECM/PCM, power to the injectors, and power for the PGM-FI main relay 2. 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 running.

Intake Air System


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

Throttle Body

The throttle body is a single-barrel side draft type. The lower portion of the IAC valve is heated by engine coolant from the cylinder head.

 

Intake Air Bypass Control Thermal Valve

When the engine is running, the intake air bypass control thermal valve sends air to the injector.

 

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), dinitrogen (N2), and water vapor.

KG, KS, KE, KR, KU, KZ, FO, KQ, models: 

KN, KM, KY, MA, PH, IN, KK models: 

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 back into the engine and burned (refer to the System Diagram to see the functional layout of the system).

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:

 

Intake Air System Diagram


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

 

Intake Manifold Runner Control (IMRC) System


Satisfactory power performance is achieved by closing and opening the Intake Manifold Runner Control (IMRC) valve. High torque at low engine speed is achieved when the valve is closed, whereas high power at high engine is achieved when the valve is opened.




 

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 EVAP canister into the engine and burned.