Honda 2004 Odyssey Service Manual page 356

Primary Heated Oxygen Sensors (Primary HO2S)
The primary HO2S detects the oxygen content in the
exhaust gas and sends signals to the 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 exhaust pipe.
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 PCM sets a DTC.
ZIRCONIA
ELEMENT
HEATER
Secondary Heated Oxygen Sensors (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 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.
ZIRCONIA
ELEMENT
HEATER
Starting Control
When the engine is started, the PCM provides a rich
mixture by increasing fuel 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 PCM. The TP
sensor is not available separately from the throttle body.
SENSOR
TERMINALS
Idle Control System
When the engine is cold, the A/C compressor is on, the
HEATER
transmission is in gear, the brake pedal is pressed, the
TERMINALS
power steering load is high, or the alternator is
charging, the PCM controls current to the IAC valve to
maintain the correct idle speed. Refer to the System
Diagram to see a functional layout of the system.
Brake Pedal Position Switch
The BPP switch signals the PCM when the brake pedal
is pressed.
Idle Air Control (IAC) Valve
To maintain proper idle speed, the IAC valve changes
SENSOR
the amount of air bypassing the throttle body in
TERMINALS
response to an electrical signal from the PCM.
HEATER
TERMINALS
BRUSH HOLDER
INNER
BUSHING
From AIR
CLEANER
VALVE
BRUSH
RESISTOR
TERMINAL
To INTAKE
MANIFOLD
(cont'd)
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