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Valve timing electronic control (VTEC) oil pressure switch
What Does the Valve timing electronic control (VTEC) oil pressure switch 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, an oil pressure switch is employed to monitor the status of the VTEC system, as opposed to monitoring the actual oil pressure in the VTEC system.
Why is the Valve timing electronic control (VTEC) oil pressure switch 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, since the PCM cannot monitor the actual operation of the VTEC system via position switches, it uses a dedicated oil pressure switch to determine whether (or not) the system’s status had changed in response to an activation command.
In terms of operation, the oil pressure switch is normally open, which indicates to the PCM that the VTEC system is not in operation. When the VTEC system is commanded ON (and the system works as expected) the voltage through the pressure switch drops to zero. The zero value serves as an indicator to the PCM that the VTEC system’s status had changed from inactive to active.
The process reverses when the engine speed drops below a certain threshold. The PCM deactivates the VTEC system, which removes oil pressure from the oil pressure switch. This returns the oil pressure switch to its normally- open state, which serves as a signal to the PCM that the VTEC system is no longer in operation.
NOTE: Several modifications and improvements had been made 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) oil pressure switch Work?
In terms of operating principles, the VTEC oil pressure switch is no different from most other oil pressure switches.
Put simply, the incoming oil pressure acts on a spring, and when the oil pressure overcomes the spring tension, the spring acts on a diaphragm that completes an electrical circuit when it touches the internal electrical contacts. In the case of VTEC oil pressure witches, however, the internal contacts are normally open, meaning that no current can flow through the switch.
When the PCM commands the VTEC system “ON”, the incoming oil pressure acts on the diaphragm via a spring until the diaphragm touches two internal electrical contacts, which closes an internal circuit. This allows the control current to flow through the switch, thereby alerting the PCM that the status of the VTEC system had changed. The process is reversed when the PCM deactivates the VTEC system.
Where is the Valve timing electronic control (VTEC) oil pressure switch Located on the Engine?
This image shows the location of the VTEC oil pressure switch on a 2004 Honda CRV engine. Note, though, that while the actual location of VTEC oil pressure switches varies somewhat between different Honda models, the pressure switch will always be located on the cylinder head, and close to the intake camshaft.
Note though that accessing the VTEC oil pressure witch 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 switch on the left side of the cylinder heads. The best way to access the pressure switch 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.
Note 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) oil pressure switch Look Like?
This image shows the oil pressure switch (arrowed) relative to the oil control solenoid on the housing that accommodates both components. The image below shows what the oil pressure switch looks like when it is removed from the housing-
While all VTEC oil pressure switches may appear to be identical in all respects, these switches are, in fact, not all the same. Apart from different calibrations, some pressure switches have different threads, which means that some pressure switches will not fit on some engines. Pay particular attention to this aspect when you purchase a replacement pressure switch because forcing incompatible threads into each other will cause irreparable damage to both the pressure switch and the housing.
Note also that Honda engines made for the Japanese domestic market do not have VTEC oil pressure switches.
What are the Symptoms that the Valve timing electronic control (VTEC) oil pressure switch is Bad?
The most common symptoms of a bad VTEC oil pressure switch are much the same across all Honda applications but note that what might appear to be some pressure switch failures and/or malfunctions do not necessarily involve actual failures of the pressure switch. 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 pressure switch-
- 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) oil pressure switch?
While it is possible to test the operation of the VTEC oil pressure switch on a DIY basis simply by verifying the switch’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 pressure switch. 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
- Defective oil pressure control solenoid
- Excessive mechanical wear of valve train components
- PCM failures and/or malfunctions
- A defective, failed, or failing VTEC oil control solenoid
- 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 solenoid control solenoid assembly
Note that while most, if not all of the above issues can mimic the effects of a failed or defective VTEC oil pressure switch, 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 pressure switch issues.
How do you replace the Valve timing electronic control (VTEC) oil pressure switch?
As mentioned elsewhere, it can be difficult to access the VTEC oil pressure switch on some Honda models. Nonetheless, even on models that offer relatively easy access to the pressure switch, you may require special tools to unscrew the switch from the control solenoid assembly 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
While the actual replacement is simply a matter of unscrewing the old switch and screwing in a replacement, for most non-professional mechanics, the effort involved in actually accessing the pressure switch is often far more trouble than it is worth. Therefore, we recommend that you seek professional assistance with replacing a suspected defective VTEC oil pressure switch.