VTEC/VTC System Description

For locations of each component on the vehicle, refer to the Component Location Index .

VTEC 

Overview 

This VTEC system changes the exhaust valve lift timing and lift height depending on the engine speed and load in order to optimize the fuel efficiency and the engine output. The rocker arm oil control solenoid switches the VTEC system on and off; the solenoid is controlled by the PCM.

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Construction 

VTEC is composed of the VTEC camshaft, VTEC rocker arm, and rocker arm oil control valve.

Control 

Based on the vehicle speed signal, engine speed signal, engine load signal, throttle position signal, and engine coolant signal sent from various sensors, the PCM determines the lift amount and controls the ON/OFF of the rocker arm oil control solenoid. The PCM generates and determines the control amount based on signals from various sensors to subject the rocker arm oil control solenoid to a feedback control.

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Operation 

At low engine speed 

At low engine speed, the rocker arm oil control solenoid is turned off by the PCM. Oil pressure from the rocker arm oil control valve does not enter the intake rocker shaft. The primary and the secondary intake rocker arms are lifted by the low lift cam lobe.

Rocker Arm Oil Control Solenoid OFF 

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At high engine speed/high load operation 

At high engine speed, the rocker arm oil control solenoid is turned on by the PCM. Oil pressure from the rocker arm oil control solenoid enters the intake primary rocker arm via the intake rocker shaft, and it moves the VTEC switching piston in the rocker arm. This causes the VTEC switching piston to slide into the intake mid rocker arm, locking the intake secondary and mid rocker arms together. Both intake rocker arms are lifted by the high lift cam lobe.

Rocker Arm Oil Control Solenoid ON 

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VTC 

Overview 

The VTC system makes continuous intake and exhaust valve timing changes depending on the engine speed, engine load, and vehicle speed.

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Control 

The VTC system diagram is as follows. The PCM advances or retards the valve timing based on the data from various sensors, and performs feedback-control to the VTC oil control solenoid valves.

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Operation 

Advance Rotation Operation 

When the advance chamber is charged with pressured oil from the VTC oil control solenoid valve, the camshaft rotates to the advanced side. When there is no oil pressure (engine is stopped), the VTC actuator B is locked in the most advanced position by the return spring and the lock pin.

Intake Side (VTC Actuator A, VTC Oil Control Solenoid Valve A) 

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Exhaust Side (VTC Actuator B, VTC Oil Control Solenoid Valve B) 

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Retard Rotation Operation 

When the retard chamber is charged with pressured oil from the VTC oil control solenoid valve, the camshaft rotates to the retarded side. When there is no oil pressure (engine is stopped), the VTC actuator A is locked in the most retarded position by the lock pin.

Intake Side (VTC Actuator A, VTC Oil Control Solenoid Valve A) 

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Exhaust Side (VTC Actuator B, VTC Oil Control Solenoid Valve B) 

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