VTEC System - General Information

The VTEC system was developed by Honda engineers to provide dynamic control of valve timing and valve lift. Engines equipped with this system are marked with the VTEC lettering cast into the cylinder head cover. All V6 engines used on the vehicle models covered by this manual are equipped with the VTEC system.

The difference between VTEC-equipped engines and the base version lies solely in the principle of valve timing control and the design features of the valve train.

The engine control module of VTEC-equipped models is able to adjust the timing and lift of the intake valves by using camshaft lobes of different size and shape. Depending on data received from the information sensors, the module either engages or disengages the system.

VTEC system operation is determined by the following input parameters:

a) Engine speed (rpm);
b) Vehicle speed (mph);
c) Throttle Position (TP) sensor output signal;
d) Current engine load, determined from the Manifold Absolute Pressure (MAP) sensor reading;
e) Engine coolant temperature.

The camshaft has three lobes for actuating each intake valve of the engine, differing in profile shape and lift height, which determine the duration and amount of opening of the corresponding valves.

At low engine speed, the secondary intake valves are actuated by their own camshaft lobes, which have very low lift and a pointed shape (i.e., compared with the primary valves, these valves open only slightly and for a very short time), keeping the atomized fuel from pooling inside the cylinder head. This produces good low-end torque with fast response, which provides excellent traction and high vehicle responsiveness. The primary lobes operate in normal mode during this time, creating swirl of the air-fuel mixture in the combustion chambers.

When higher engine output is required, the secondary rocker arms are locked to the primary rocker arms by special synchronizing pistons. The synchronizing pistons are hydraulically actuated and electronically controlled. When the rocker arms are locked, both intake valves begin to open in the same manner, and the amount and duration of their opening are determined by the profile of the intermediate rocker arm lobe and are at a higher level.

The secondary rocker arms stop contacting their own lobes until the system is disengaged. In this condition, both valves open to full lift and maximum duration, providing increased engine speed and output.
Component Inspection


Inspection of some VTEC components requires removal of the rocker arm assembly (refer to Rocker Arm Assembly Removal, Inspection and Installation).