TechASSIST: Camshaft Adjustment Control Valves

The camshaft adjustment valve (also known as an oil control valve) is an integral part of the variable valve timing (VVT) system in modern engines. Each manufacturer has different technology and terminology for the system, some of the most recognisable names include VVT, VVTi, VTEC and VTi (For a full list please see Table 1). Many of which have been introduced with iconic VVT milestone vehicles.

There will also be some differences between manufacturers as to how the systems operate but fundamentally the concept remains the same…

So what is variable valve timing?

To understand how camshaft adjustment valves operate it is important to first understand the concept of variable valve timing.

In simplest terms, variable valve timing or camshaft adjustment advances or retards the opening times of valves in the engine to adapt to a range of operating conditions and desired results. As a result the operating efficiency of intake and exhaust valves  is greatly increased which in turn results in:

• Reduced fuel consumption
• Increased torque at lower engine speed
• Improved horsepower at higher engine speeds
• Internal exhaust gas recirculation
• Reduced harmful exhaust emissions

How do camshaft adjustment valves work?

Generally variable valve timing is controlled by oil pressure. The engine’s ECU/PCM uses a host of sensors including the camshaft sensor and mass airflow sensor to calculate the required valve timing based on the current driving conditions. This is communicated as a pulse width signal to the camshaft adjustment valve which then controls the flow of oil. The valve is able to direct the flow of oil to the VVT hub by using an integrated solenoid and spool valve to advance or retard valve timing.

Why do camshaft adjustment valves fail?

The camshaft adjustment valve is a mechanical, hydraulic and electronic component, so there are many causes of failure including:

• Contaminated, degraded, poor quality or incorrect engine oil can cause slow operation or seizure of the valve. This is one of the most common causes, usually as a result of missed or poor servicing.
• Damage to the electrical circuits, wiring or connectors.
• Natural wear to the valves internal gears and seals over time 

Also check for:

• Low engine oil pressure causing incorrect operation of the adjustment valves.
• Wear or slack in the timing chain/belt causing incorrect valve timing.

Symptoms of a faulty camshaft adjustment control valve

1. Check Engine Lights – in many cases, modern vehicles will recognise a fault, illuminate the check engine light and report the relevant error code. P0011 ‘Camshaft Position “A” – Timing Over-Advanced or System Performance (Bank 1)’ is common.
2. Rough Idle – A key role of the valve is to maintain a smooth engine when idling. If the valve is stuck in a retarded position the RPM will drop too low and may stall the engine.
3. Rough Acceleration and Misfires – Again, the valve ensures smooth engine performance throughout the RPM range. If stuck, acceleration will feel rough and there may be misfires.
4. Increased Fuel Consumption – If the valve is not functioning, fuel efficiency will suffer resulting in lower average MPG.
5. Poor Performance – The valve serves to improve performance by adjusting to suit driving conditions. Without it the driver will notice lower overall performance.

Table 1: Variable Valve Technology by Manufacturer

Form more information please contact ELTA Automotive on +44 (0)1675 466 999 or email sales@elta.co.uk