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Oil Pressure Switch
What Does the Oil Pressure Switch Do?
Also known as, the “Oil Pressure Sender Unit” or less commonly as the “Oil Pressure Sensor”, the function of the Oil Pressure Switch is to monitor the level of oil pressure in the engine’s oil circulation system.
Why is the Oil Pressure Switch Needed?
The lubrication requirements of modern engines demand that all moving parts of the engine be supplied with sufficient quantities of lubricating oil not only to prevent metal-to-metal contact between moving parts but also to assist in the cooling of some parts, including pistons and cylinder walls.
Therefore, all engines use high-volume, engine-driven oil pumps to deliver lubricating oil at pressures and volumes that meet the engine’s lubrication requirements. However, while modern oil pumps can deliver high oil flow rates and volumes, the actual flow rate and volume of oil being transported at any given moment are dependent on three important parameters, these parameters being-
- The viscosity of the oil, as a function of the oil’s temperature: the colder the oil is, the more difficult it is to pump around the engine. Conversely, the hotter the oil becomes, the easier it becomes to pump around the engine
- The engine speed, because the volume of oil an oil pump can displace during one revolution (of the pump) is fixed. As a result, a low engine speed will displace less oil per minute than an engine running at high speed will
- The mechanical condition of the engine, with reference to the amount of mechanical wear between sliding components. This is perhaps the most important parameter that determines an engine’s oil pressure, because the bigger the clearances between sliding components become, the more oil is passed through the enlarged clearances. Thus, when clearances become excessively large, some parts of the engine may be starved of lubrication because most of the available oil is pumped through excessively large clearances
In practice, an engine’s lubrication system has many “holes” between sliding components to ensure that all moving parts always receive sufficient quantities of lubricating oil. However, since these “holes” (for the most part) terminate in the gap between sliding surfaces, the clearances between the sliding surfaces act as restrictions to the oil flow to maintain pressure in the oil circulation system, while ensuring sufficient lubrication, at the same time.
As a practical matter, though, the engine management system cannot monitor or measure the pressure in the oil circulation system directly except through using one, or sometimes more, dedicated pressure switches that are located at various points in the oil circulation system.
On some applications, such as those that use pressurized engine oil to activate or control variable valve timing, or variable camshaft timing systems, the actual pressure in the circulation system becomes even more important. On these engines, the engine management system directs pressurized oil to actuators through dedicated oil control solenoids, and if there is insufficient oil pressure present, the actuators that adjust the valve or camshaft timing cannot function. Therefore, the engine management system depends on input data from the Oil Pressure Switch to control critically important engine management functions.
How Does the Oil Pressure Switch Work?
This image shows a simplified schematic diagram of the inner workings of the most common type of Oil Pressure Switch in use today.
As shown here, the pressurized oil enters the Switch from the bottom and pushes against a spring-loaded diaphragm. As the oil pressure rises, the oil pushes the diaphragm up against the spring tension until the diaphragm closes a circuit, which extinguishes the oil warning light on the dashboard.
Conversely, when the oil pressure decreases, such as when the engine is switched off, the internal springs force the diaphragm back down: this opens the internal circuit to cause the oil warning light to come on again.
Note that Oil Pressure Switches are calibrated differently for different engines, even though any given two Oil Pressure Switches may appear to be identical from the outside. The problem is that while all Oil Pressure Switches monitor the oil pressure continuously while the engine is running, the point at which the internal spring tension overcomes the effect of the oil pressure is different for different engine types and designs.
Put differently, this means that while Oil Pressure Switches do not affect the actual oil pressure in any way, using the wrong, or an unsuitable Oil Pressure Switch could generate false warnings of low oil pressure. Thus, while the actual oil pressure on an engine with variable valve timing might be sufficient to activate and control the system, the engine management system might deactivate the system based on invalid input data from an unsuitable Oil Pressure Switch.
If this happens, the engine management system might initiate and enforce a limp mode, which severely limits the engine’s power output as a safety precaution. In some instances, the engine management system might even force the engine to shut down, which has obvious negative consequences.
NOTE: One other type of Oil Pressure sensor works by converting the oil pressure it senses into an electrical signal, which the PCM (Powertrain Control Module) uses to calculate a numerical value. In these designs, the actual oil pressure is displayed on an instrument on the dashboard much like a fuel gauge displays the fuel level.
These types of Oil pressure Switches typically have two, or sometimes three wires, one of which is usually a ground, while one connects to the OIL warning light, and the other connecting to the PCM.
Where is the Oil Pressure Switch Located on the Engine?
This image shows the location (arrowed) of the Oil Pressure Switch on a Ford Bronco application. Note though that, while the Oil Pressure Switch on many, if not most applications are located on, or close to the oil filter, the actual location of these switches vary greatly not only between different manufacturers but also between models from the same manufacturer.
Thus, on many applications, the Oil Pressure Switch can be located somewhere on the cylinder block, or in some cases, on the cylinder head(s). Note also that on some applications, such as many VAG-group vehicles, there may be two Oil Pressure Switches installed; one to monitor high pressure, and one to activate a dedicated (audible) alarm if the oil pressure drops below a minimum allowable threshold. In these cases, the two sensors have different calibrations and are therefore NOT interchangeable.
Because the locations of Oil Pressure Sensors vary so widely, we strongly recommend that you research the exact location of the sensor on your particular vehicle very thoroughly because Oil Pressure Sensors sometimes resemble Engine Coolant and Knock Sensors very closely, so it is easy to replace the wrong sensor.
What Does the Oil Pressure Switch Look Like?
This image shows a typical example of an Oil Pressure Switch; in this case, this switch is suitable for use on a range of Jeep models.
Note though that while most Oil Pressure Switch designs follow this general pattern, the actual appearance of both the switch and its electrical connector can vary greatly from the example shown here. As a result, we recommend that you only purchase replacement Oil Pressure Switches from an authorized dealership to ensure you buy the correct switch for your particular vehicle and model.
While there are many aftermarket replacement brands available, bear in mind that there is also plenty of room for mistakes in terms of how a particular aftermarket replacement switch is calibrated. Thus, if you decide to use an aftermarket replacement Oil Pressure Switch, be sure to only deal with reputable dealers that supply OEM-equivalent parts.
What are the Symptoms that the Oil Pressure Switch is Bad?
The most common symptoms of bad or failing Oil Pressure Switches are much the same across all applications. These could include the following, but note that the symptoms listed here assume that a) the Oil Pressure Switch is defective, and b), that the actual oil pressure is within specifications, but the Oil Pressure Switch is supplying the PCM with invalid input data-
- Illuminated OIL warning light, and possibly, multiple stored trouble codes on engines that are fitted with variable valve timing systems
- There may be evidence of an oil leak at, or around the Oil Pressure Switch if it is leaking, which is perhaps the most common failure of these switches
- On engines with VVT /VCT (variable valve Timing/Variable Camshaft Timing) systems, the engine may run roughly at some engine speeds, or the engine may be hard to start- depending on both the application and the nature of the VVT/VCT control system
- On engines with VVT /VCT (variable Valve Timing/Variable Camshaft Timing) systems, the engine management system may initiate and enforce either a no-start condition or a limp mode to protect the engine against damage
NOTE: While the symptoms listed above can result from false or invalid input data from a defective Oil Pressure Switch, they can also result from-
- Insufficient oil pressure
- The use of dirty, degraded, contaminated, or unsuitable engine oil
- Low oil level
- Blocked or dirty oil filter
- Stuck open or defective oil pressure relief valve
- Burnt, damaged, shorted, disconnected, or corroded wiring and/connectors in the Oil Pressure Switch wiring
How do you test the Oil Pressure Switch?
While there are some basic tests one can perform to verify the condition of a suspect Oil Pressure Switch, we do not recommend this course of action for the average DIY mechanic. Oil Pressure Switch calibrations vary too much for electrical resistance values obtained on a DIY basis to have conclusive diagnostic value. Similarly, using compressed air to “inflate” the Switch to see if it switches between “open” and “closed” states can, and usually does produce misleading and/or inaccurate results.
To confirm an Oil Pressure Switch as defective (or not), the actual oil pressure on the engine has to be checked and verified with a dedicated pressure gauge before an Oil Pressure Switch is condemned out of hand. In short, doing this test requires tools, equipment, and knowledge that the average home mechanic typically does not own or have access to.
Therefore, if you suspect that you have a faulty, defective, or malfunctioning Oil Pressure Switch, we strongly recommend that you seek professional assistance with diagnosing and repairing the problem definitively. Making a mistake could cause extensive, immediate, and almost always fatal engine damage.
How do you replace the Oil Pressure Switch?
While replacing an Oil Pressure Switch is usually as easy as unscrewing the old unit from the engine and screwing in a replacement, the fact is that in nine out of every ten cases, you need to remove unrelated engine parts/components to give you enough room to swing a wrench in. Moreover, if the Oil Pressure Switch is fitted with a wiring harness, you also need a special tool to unscrew the old switch and to screw the new unit into place without damaging the attached wiring.
While this is possible to do on a DIY basis on many vehicles, working space in most modern engine compartments is extremely limited, and an Oil Pressure Switch replacement can often be challenging even for professional mechanics. Therefore, we strongly recommend that you seek professional assistance with the replacement to avoid causing damage not only to the new Oil Pressure Switch but also to unrelated wiring and/or engine parts and components.