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Engine Oil Pressure Switch
1. Introduction of Oil Pressure Switch
Oil pressure switches are typically used as an actuator which directly activates the oil warning light in driver dashboard when the oil pressure in the engine will fall below the preset critical level or brings a signal to the ECU (engine control unit), so to be warned about low pressure of engine oil and prevent damage to the engine.
Oil pressure switches are typically used as an actuator which directly activates the oil warning light in driver dashboard when the oil pressure in the engine will fall below the preset critical level or brings a signal to the ECU (engine control unit), so to be warned about low pressure of engine oil and prevent damage to the engine.
Depending on the engine construction, the oil pressure switch usually can be found in one of the most common locations: in the cylinder block of the engine or in the oil filter housing as well as at some engine types can be found in the engine head.
2. Operating Principles
The switch is operated by a self-elastic diaphragm or movable diaphragm with fitted hairspring, whose position is determined by the pressure applied to it. The required critical pressure for moving up the diaphragm and activating (Switching ON or switching OFF) the switch contacts is determined by the oil pressure of the engine. This critical value of oil pressure is individual for every engine type and can vary. Usual value is between 0.25 and 0.75 bar.
If the oil pressure falls below this critical value, the switch directly activates the oil warning light in driver dashboard or in some engine management systems the switch returns a signal to the ECU, so to be warned about low pressure of engine oil and prevent damage to the engine. The switch contacts can be either normally open or normally closed.
The switch is operated by a self-elastic diaphragm or movable diaphragm with fitted hairspring, whose position is determined by the pressure applied to it. The required critical pressure for moving up the diaphragm and activating (Switching ON or switching OFF) the switch contacts is determined by the oil pressure of the engine. This critical value of oil pressure is individual for every engine type and can vary. Usual value is between 0.25 and 0.75 bar.
If the oil pressure falls below this critical value, the switch directly activates the oil warning light in driver dashboard or in some engine management systems the switch returns a signal to the ECU, so to be warned about low pressure of engine oil and prevent damage to the engine. The switch contacts can be either normally open or normally closed.
1. Washer for sealing, 2. Diaphragm, 3. Switch housing, 4. Connector
5. Switch contacts (A normally open, B normally closed), 6. Thread for tightness.
(A) shows illustrative drawing of one type of oil pressure switch with normally open contacts, and (B) one type of switch with normally closed contacts. The operation of these types of switches is fundamentally similar in all instances, although the type, size and construction can vary upon the manufacturer application or requirement of a used system.
At the switches with normally open contacts, when the engine oil pressure reaches the preset critical level, produces movement of the diaphragm and activates the contacts of the switch, so the contacts are connected together, i.e. the switch is closed (Switched ON). The switches with normally closed contacts works opposite, when the engine oil pressure reaches the preset critical level, deactivates the already connected contacts of the switch, so now the contacts are disconnected, i.e. the switch is open (Switched OFF).
At the switches with normally open contacts, when the engine oil pressure reaches the preset critical level, produces movement of the diaphragm and activates the contacts of the switch, so the contacts are connected together, i.e. the switch is closed (Switched ON). The switches with normally closed contacts works opposite, when the engine oil pressure reaches the preset critical level, deactivates the already connected contacts of the switch, so now the contacts are disconnected, i.e. the switch is open (Switched OFF).
3. Diagnostics and Testing Procedures
Switch with Normally Open Contacts
• Check that there is an open circuit between the contacts when the engine is not running.
• Check that there is a short circuit (continuity) between the contacts when the engine is running.
• Check the continuity and condition of the pins, terminals and wires.
Switch with Normally Closed Contacts
• Check that there is a short circuit (continuity) between the contacts when the engine is not running.
• Check that there is an open circuit between the contacts when the engine is running.
• Check the continuity and condition of the pins, terminals and wires.
Switch with Normally Open Contacts
• Check that there is an open circuit between the contacts when the engine is not running.
• Check that there is a short circuit (continuity) between the contacts when the engine is running.
• Check the continuity and condition of the pins, terminals and wires.
Switch with Normally Closed Contacts
• Check that there is a short circuit (continuity) between the contacts when the engine is not running.
• Check that there is an open circuit between the contacts when the engine is running.
• Check the continuity and condition of the pins, terminals and wires.
4. Testing Procedures with Multimeter
Unplug the connector from oil pressure switch and check the connectivity between the contacts. If the switch is with two pins, the check should be between the pins. In case when the switch is with only one pin, then the check should be between the pin and mass (negative pole).
When the engine is not running, the read value of the electrical resistance from a multimeter in case of switch with normally open contacts should be infinite (contacts are disconnected – switched OFF), and in case of switch with normally closed contacts should be zero (contacts are connected – switched ON).
When the engine is running, the read value of the electrical resistance from a multimeter in case of switch with normally open contacts should be zero (contacts are connected – switched ON), and in case of switch with normally closed contacts should be infinite (contacts are disconnected – switched OFF).
Unplug the connector from oil pressure switch and check the connectivity between the contacts. If the switch is with two pins, the check should be between the pins. In case when the switch is with only one pin, then the check should be between the pin and mass (negative pole).
When the engine is not running, the read value of the electrical resistance from a multimeter in case of switch with normally open contacts should be infinite (contacts are disconnected – switched OFF), and in case of switch with normally closed contacts should be zero (contacts are connected – switched ON).
When the engine is running, the read value of the electrical resistance from a multimeter in case of switch with normally open contacts should be zero (contacts are connected – switched ON), and in case of switch with normally closed contacts should be infinite (contacts are disconnected – switched OFF).
