Manifold Absolute Pressure (MAP) Sensor
Malfunction Indicator Lamp (MIL) Indication (In relation
to Readiness Codes)
Mass Air Flow (MAF) Sensor/Intake Air Temperature
Output Shaft (Countershaft) Speed Sensor
Fuel and Emissions Systems
The knock control system adjusts the ignition timing to
The MAP sensor converts manifold absolute pressure
into electrical signals to the ECM/PCM.
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 (see page 11-69).
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 change 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.
This sensor detects countershaft speed.
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Secondary Heated Oxygen Sensor (Secondary HO2S)
Accelerator Pedal Position (APP) Sensor
Electronic Throttle Control System
APP SENSOR A/B
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.
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)
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.
As the accelerator pedal position changes, the sensor
varies the signal voltage to the ECM/PCM.
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Brake Pedal Position Switch
Electrical Power Steering (EPS) Signal
Fuel Cutoff Control
Fuel Pump Control
PGM-FI Main Relay 1 and 2
Idle Control System
Fuel Supply System
Fuel and Emissions Systems
(TP) SENSOR and
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
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 signal to the throttle
position to maintain the correct idle speed.
The brake pedal position switch signals the ECM/PCM
when the brake pedal is pressed.
The EPS signals the ECM/PCM when the power steering
load is high.
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. Fuel cutoff
control also occurs when the engine speed exceeds
6,900 rpm (K20Z3: 8,200 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
(K20Z3: 7,700 rpm). On a cold engine, fuel cut occurs at
a lower engine speed.
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 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 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.
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LOW SPEED CAM
HIGH SPEED CAM
• The i-VTEC system has a variable valve timing control (VTC) mechanism on the intake camshaft in addition to the
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 VTC system changes the phase of the intake camshaft via oil pressure. It changes the intake valve timing
For stable combustion, the cam angle is retarded, and
reduces the entry of exhaust gas into the cylinder.
Cam phase angle is controlled to optimize valve
timing, improving fuel efficiency and reducing
To reduce pumping loss, the intake valve is closed
quickly. This gives the air/fuel mixture a charging
effect that helps to maximize engine power.
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