What Does the Valve timing electronic control (VTEC) solenoid Do?
Honda vehicles use a variable valve timing system known as VTEC, which stands for Variable Valve Timing with Electronic Control. Briefly, since this system uses pressurized engine oil to activate the valve timing system, the PCM (Powertrain Control Module) uses a control solenoid to control the flow of oil to the VTEC system.
Why is the Valve timing electronic control (VTEC) solenoid Needed?
We need not delve into the complexities of how VTEC systems on Honda vehicles work here, beyond saying that at engine speeds of about 4000 RPM, the PCM (Powertrain Control Module) activates the VTEC system to increase the engine’s volumetric efficiency.
In simple terms, this means that the PCM activates a system that increases the intake valves’ opening by switching the rocker arms to follow higher cam lobes. This means that the intake valves open earlier, stay open for longer, and achieve bigger openings than is possible with lower cam lobe profiles. In practice, bigger valve openings mean that the cylinders draw in more air, which improves combustion through improved mixing of the air and fuel.
The effect of this change is that engine efficiencies improve at high engine speeds without a commensurate fuel consumption penalty.
As a practical matter, the PCM accomplishes the switching between different cam lobe profiles by energizing an oil control solenoid that directs pressurized engine oil to the intake camshaft to activate the VTEC system. However, the PCM can only activate the VTEC system if certain preconditions such as, among others, a minimum engine speed/load, vehicle speed, and the throttle position are satisfied.
Thus, like all other variable valve timing systems, the PCM monitors input data from several engine sensors, and when conditions allow, the PCM energizes the VTEC control solenoid to allow pressurized engine oil to activate the VTEC system. As a practical matter, the PCM will keep the VTEC control solenoid open to maintain oil pressure on the system to keep the VTEC system in operation for as long as all preconditions for its operation are met.
When operating conditions no longer allow the operation of the VTEC system, such as when the engine speed drops below a minimum threshold, the PCM de-energizes the VTEC control solenoid, which does two things. The first thing is that oil pressure is removed from the VTEC system, thereby deactivating it, and the second thing is that the VTEC system is isolated from the engine’s oil circulation system, thus preventing activation of the VTEC system until all required enabling conditions are met again.
Based on the above, it should be clear that the correct operation of the VTEC system depends entirely on how effectively the PCM can control the operation of the VTEC oil control solenoid. Put differently; unless the VTEC control solenoid can switch the VTEC systems’ oil supply “ON” and “OFF” reliably and predictably, the PCM cannot control the operation of the VTEC system. IN such cases, the PCM will set one or more fault codes, and disable the VTEC system until the fault is found and corrected.
NOTE: Honda had made several modifications and improvements to the VTEC system since it was first introduced in 1991. The most significant of these improvements is using a variable camshaft timing system that can adjust the intake valve timing through a range of 25 degrees. This innovation greatly improves the engine’s efficiency over a much wider range of engine speeds than was possible to do with only the VTEC system.
How Does the Valve timing electronic control (VTEC) solenoid Work?
In terms of operating principles, VTEC 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 or inadvertent movement of the plunger.
In practice, the plunger (aka spool valve) on VTEC 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 VTEC system. When the PCM reverses the command, the plunger moves in the opposite direction to remove oil pressure from the VTEC system, which deactivates the VTEC system and isolates it from the engine’s oil circulation system.
Where is the Valve timing electronic control (VTEC) solenoid Located on the Engine?
This image shows the location (arrowed) of the VTEC oil control solenoid assembly on a 2004 Honda Civic engine. Note that although the actual location of VTEC oil control solenoids varies somewhat between different Honda models, the control solenoid assembly will always be located on the cylinder head, and close to the intake camshaft.
Note, though, that accessing the VTEC oil control solenoid assembly on some Honda models, including Civic SI and Accord models with2.3 L or 2.4 L four-cylinder engines, can be difficult because of the location of the assembly on the left side of the cylinder heads. The best way to access the oil control solenoid on these models is to remove the entire VTEC control solenoid assembly from the engine, but note that this requires a new gasket when you reinstall the assembly. Be aware that failing to replace this gasket will result in oil leaks that could cause the VTEC system to stop working.
What Does the Valve timing electronic control (VTEC) solenoid Look Like?
This image shows the VTEC oil control solenoid (arrowed in green) relative to the VTEC oil pressure switch on the oil control assembly.
Note that while it is possible to remove and replace only the solenoid, doing this usually requires that the whole assembly be removed from the engine to access the solenoid’s retaining screws/bolts. Moreover, while the rubber gasket shown here is new, these gaskets usually harden and shrink after a few years of use, meaning that replacing the assembly with the old gasket virtually guarantees an oil leak afterward.
Therefore, we recommend that when you replace a VTEC oil control solenoid, you replace the entire assembly to ensure that the pressure switch and the solenoid are matched and that the new gasket prevents oil leaks.
What are the Symptoms that the Valve timing electronic control (VTEC) solenoid is Bad?
The most common symptoms of a bad VTEC oil control solenoid are much the same across all Honda 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 and illuminated warning light, with the most common trouble code (by far) being P1259 – “VTEC system malfunction”. Note that this particular trouble code can be set as the result of a wide variety of possible causes, which may or may not include a failure of the oil control solenoid
- 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 pressure switch may leak oil, and in serious cases, the leak may prevent the operation of the VTEC system, which may or may not set VTEC-related trouble codes
How do you test the Valve timing electronic control (VTEC) solenoid?
It is possible to test the operation of the VTEC 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 VTEC oil control solenoid, but note that 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 occur inside the VTEC oil control assembly
Note that while most, if not all of the above issues can mimic the effects of a failed or defective VTEC oil control solenoid, most of these issues will also not set trouble codes. Therefore, unless you are a skilled mechanic, we recommend that you seek professional assistance to diagnose and repair suspected VTEC oil control solenoid issues.
How do you replace the Valve timing electronic control (VTEC) solenoid?
As mentioned elsewhere, it can be challenging to access the VTEC oil control solenoid on some Honda 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 unscrewing the old oil control assembly and installing a replacement. However, the effort involved in accessing the oil control assembly (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 suspected defective VTEC oil control components.