What Does the Valve timing control (VTC) oil control solenoid Do?
As their name suggests, the function of VTC (Valve Timing Control) solenoids is to control the flow of pressurized engine oil to and from the actuators that ultimately control variable valve timing systems.
Why is the Valve timing control (VTC) oil control solenoid Needed?
Except for systems on Honda* and some VAG-group engines that employ different camshaft profiles to vary or change the valve timing, most VVT (Variable Valve Timing) and /or VCT (variable Camshaft Timing) systems use actuators to rotate camshafts with fixed profiles relative to a set reference point to change the valve timing.
*Honda had recently introduced the i-VTEC system, which, like most other VVT systems, employs an actuator to rotate the intake camshaft, in addition to the existing system that switches between high and low camshaft lobe profiles.
In practice, changing the valve timing, i.e., advancing or retarding the valve timing in respect of the position of the pistons changes the engine’s volumetric efficiency. Put differently, this means that by opening and closing valves earlier or later (depending on current operating conditions), it is possible to make engines more efficient at high engine speeds than they would be with standard valve timing settings.
One reason for improved efficiencies is that by opening intake valves earlier (relative to the position of the pistons), more air can be drawn into the cylinders. Similarly, by keeping intake valves open for longer (again, relative to the position of the pistons), the mixing of the air and fuel is improved, thus producing improved combustion, which in turn creates fewer harmful exhaust emissions.
However, all VVT/VCT systems have base settings, which can be thought of as the position the adjustable camshafts would be in had the engine not been fitted with a VVT system. In this base position, the engine operates efficiently at low to moderate speeds, but as both the engine speed and load increase, it becomes progressively more difficult for the cylinders to draw in enough air through the intake tract.
The first reason involves the fact that since the time that is available to draw air in reduces the faster the engine rotates, and the second reason is that the length, average diameter, and configuration of the inlet tract combine to limit the speed at which air can flow through the inlet tract.
Thus, to overcome these problems, the PCM can alter the valve timing by controlling solenoids that allow pressurized engine oil to act on actuators on the camshaft(s). The effect of the pressurized oil is to rotate the camshaft either against or along the direction of rotation (of the camshaft) to advance or retard the valve timing.
When the PCM activates the VVT/VCT system, it opens an oil control solenoid to allow oil to act on the actuator. However, the PCM monitors the degree of rotation with a sensor known as the CMP (Camshaft Position Sensor, which is referenced to the CKP (Crankshaft Position Sensor). We need not delve into the complexities of this correlation here, beyond saying that the PCM monitors the position of the (now adjusted) camshaft against the positions of the pistons via the crankshaft position sensor.
When operating conditions allow, the PCM deactivates the VVT/VCT system by removing power from the oil control solenoid. This action removes oil pressure from the actuator and in a fully functional VVT/VCT system, the camshaft returns to its base position automatically. To verify this, the PCM will compare the position of the camshaft (measured in degrees of rotation) with input data from the crankshaft position sensor.
If based on current operating conditions, the data from both sensors agree, the PCM will recognize that the camshaft had returned to its rest position. As a result, the PCM will make appropriate adjustments to the fuel and ignition timing strategies to suit the valve timing setting.
Unlike Honda’s VTEC system, which produces noticeable changes in the engine’s power output, the advance or retardation of the valve timing on non-Honda engines occurs seamlessly, and most drivers are unable to detect the change in an engine’s power output if the oil control solenoids work as designed.
How Does the Valve timing control (VTC) oil control solenoid Work?
In terms of operating principles, VVT/VCT oil control solenoids are no different from any other control solenoid.
Like all other solenoids, the unit consists of an electromagnetic coil that acts on a moveable plunger within the solenoid body when the PCM energizes the coil. In addition, like all other solenoids, one or more springs hold the plunger in one position to prevent uncommanded movements of the plunger.
In practice, the plunger (aka spool valve) on VVT oil control solenoids is held in a position that blocks pressurized oil from passing through the valve part of the solenoid. Depending on the commanded position, the coil moves the plunger in one direction to allow oil to pass through the valve, thus activating the VVT/VCT system. When the PCM reverses the command, the plunger moves in the opposite direction to remove oil pressure from the VVT/VCT system, which both deactivates the VVT/VCT system and isolates it from the engine’s oil circulation system.
Where is the Valve timing control (VTC) oil control solenoid Located on the Engine?
This image shows the location (arrowed) where the VVT oil control solenoid fits on 2007 – 2013 Toyota Corolla engines. In this example, the solenoid had been removed from the engine.
Be aware that while the VVT oil control solenoid is easily accessible on this particular Toyota engine, this is not the case for most other Toyota models, or indeed, most other vehicle makes and models. In many cases, the solenoid may be located inside the valve cover, behind a timing belt cover, or in locations that require the removal and/or disassembly of other unrelated components to gain access to the solenoid.
Thus, since the location of VVT oil control solenoids varies greatly between different vehicle makes and models, we highly recommend that you obtain reliable service information for the affected vehicle to identify and locate the solenoid correctly. This is particularly important in applications that use VVT on both intake and exhaust camshafts because it is easy to test/remove/replace the wrong solenoid on these engines.
What Does the Valve timing control (VTC) oil control solenoid Look Like?
This image shows a typical VVT oil control solenoid. In this case, the solenoid is suitable for use on some Toyota Camry models.
Note though that while there are some design differences between VVT oil control solenoids for different applications, all VVT oil control solenoid designs follow this general pattern. However, even in cases where two VVT solenoids appear identical in all respects, bear in mind that VVT solenoids are not interchangeable since most VVT solenoids have application-specific calibrations.
In other words, the fact that a VVT solenoid fits on any given engine does not guarantee that it will work on that engine. Therefore, we strongly recommend that you use only OEM or OEM-equivalent replacement parts to ensure the proper operation of the VVT system.
What are the Symptoms that the Valve timing control (VTC) oil control solenoid is Bad?
The most common symptoms of a bad VVT oil control solenoid are much the same across all applications but be aware that what might appear to be a solenoid failure and/or malfunction might not necessarily involve an actual failure of the solenoid. Nonetheless, common symptoms could include one or more of the following-
- Stored trouble code(s) and illuminated warning light, with the most common trouble codes (by far) being codes that relate to camshaft/crankshaft correlation issues. Note that this category of trouble codes can be set as the result of a wide variety of possible causes, which may or may not include a failure of the VVT oil control solenoid
- A hard starting condition may be present
- In some cases, and depending on the nature of the problem, a no-start condition may be present
- The engine may lack power at high engine speeds
- The engine may run roughly at low engine speeds
- The idle quality may be poor, or the engine may not idle at all
- The engine may exhibit misfires at some engine speeds
- Fuel consumption may increase dramatically
- The oil control solenoid may leak oil, and in serious cases, the leak may prevent the operation of the VVT system, which may or may not set VVT-related trouble codes
How do you test the Valve timing control (VTC) oil control solenoid?
It is possible to test the operation of the VVT oil control solenoid on a DIY basis simply by measuring and verifying the solenoid coil’s electrical resistance and continuity. However, we do not recommend that non-professional mechanics engage in diagnostic and/or repair attempts because of the sheer number of possible causes of problems that can mimic the effects of a defective oil control solenoid. For instance, some potential causes include, but are not limited to-
- Insufficient engine oil pressure as the result of mechanical wear inside the engine
- Low oil levels
- The use of unsuitable engine oil
- The use of dirty, degraded, or contaminated engine oil that blocks the solenoid’s filter screen
- PCM failures and/or malfunctions
- A defective, failed, or failing VVT oil control solenoid, but note that actual solenoid failures are rare
- Burnt, damaged, corroded, shorted, or disconnected wiring and/or electrical connectors
- Serious oil leaks, some of which may not be detectable because they could occur inside the VVT oil control solenoid
Note that with the possible exception of camshaft/crankshaft correlation issues, most, if not all of the above issues can a) mimic the effects of a failed or defective VVT oil control solenoid and b) not set trouble codes. Therefore, unless you are a skilled mechanic, we recommend you seek professional assistance to diagnose and repair suspected VVT oil control solenoid issues.
How do you replace the Valve timing control (VTC) oil control solenoid?
As mentioned elsewhere, it can be challenging to access the VVT oil control solenoid on some models. Nonetheless, even on models that offer relatively easy access to the solenoid assembly, you may require special tools to unscrew the assembly’s retaining bolts from the engine because of-
- limited workspace in the engine compartment
- the potential to damage other parts and components while trying to force standard tools into spaces that are too small for them to fit into
The actual replacement is simply a matter of removing a single retaining bolt, removing the old solenoid from the engine, and installing a replacement. However, the effort involved in accessing the oil control solenoid (and the cost of special tools) is often far more trouble than it is worth to many non-professional mechanics. Therefore, we recommend that you seek professional assistance with diagnosing and replacing a suspected defective VVT oil control solenoid.