Welcome to our knowledge base of totally random and probably obscure stuff relating to PS262 oil pressure senders!

We've recorded these notes and observations not only for ourselves (because we forget stuff over time), but also in case anyone else can find it useful. If you find something incorrect or wish to contribute something, just let us know here.
 PS262 oil pressure sender PS262 oil pressure sender description and function
 PS262 oil pressure sender PS262 oil pressure sender common failures
 PS262 oil pressure sender PS262 oil pressure sender troubleshooting
 PS262 oil pressure sender PS262 oil pressure sender calibration

PS262 oil pressure sender description and function

This oil pressure sensor is used on a wide variety of mainly General Motors vehicles in the 1990's. It is used elsewhere, but that is the primary use. This sender is designed to both send a pressure reading, and to provide a switch cut-off to the fuel pump in the event of pressure loss. It has a three pin plug. The outer two pins provide the switch circuit, while the center pin provides the resistance reading for pressure. The sensor casing is a metal threaded base (1/4-18 NTPF) holding the diaphram chamber, with a plastic outer casing above containing the components and plug. The internal components consist of a diaphram to provide variable vertical movement within the sender upon the application of oil pressure. The diaphram acts upon a corresponding assembly that activates both the switch and the sender. The switch is activated by closing metal contacts when the diaphram reaches a certain height, i.e. certain oil pressure. The sender is activated by a lever arm that moves across a wire coil. One end of the coil is grounded through the lever arm down to the sensor base. The other end is the sender output.

When pressure is placed against the diaphragm, it rises which elevates the internal mechanism. The lever swings across the coil, altering the circuit resistance. The two switch circuit contacts on top are connected by the crossbar when it rises to a certain point. There is a small spring under the crossbar to allow play beyond this contact point.
ps262 sender function

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PS262 oil pressure sender common failures

When the oil pressure sender fails, there can be several symptoms. Obviously loss of oil pressure on the gauge, or the engine shutting off. Also there can be oil leaking from the sensor itself, at several possible points. Oil can leak around the diaphragm into the sensor, compromising the readings. The switch contacts may still close, allowing the engine to run. A sign of this problem can be good oil pressure on a cold engine, but loss of oil pressure as the engine warms up. This is because the sender casing slowly fills with oil, compromising the pressure difference behind the diaphragm.

oil can leak from the joint between the metal and plastic casing sections. It can also leak from a factory hole in the plug end, which is sealed with a drop of rubber sealant at the factory. If the plug is removed and the contacts are wet with oil, this is most likely the source of the leak since a waterproof connector is used.

internally, oil can either penetrate the diaphragm (rare), or leak around the diaphragm where it joins the casing. There is a rubber gasket here which is a common failure point. Oil can then leak into the sensor itself and compromise the reading.
ps262 sender breakdown

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PS262 oil pressure troubleshooting

Before suspecting anything else when oil pressure drops, it is easiest to check the sender first. The first thing to look for is leakage of oil from either the plug end or the o-ring seal between plastic and metal. If oil is present, the sender is most likely bad.

The outer two contacts should be a complete circuit when the engine is running; this can be verified with a meter. This checks the switch side. The resistance between the middle pin and ground can also be checked to verify the gauge reading. High resistance is at the bottom of the gauge, so if the sender is unplugged the gauge needle should fall completely. As the internal lever arm moves across the coil, resistance decreases. If the sender is removed from the vehicle, this operation can be verified by applying carefully calibrated amounts of compressed air to the sender while checking resistance with a meter. The switch contacts may be checked in a similar manner. Do not overpressurize the sender more than 60 psi or it could be damaged.

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PS262 oil pressure calibration

The switch circuit activation pressure can be adjusted without dissassembling the sender. With the plug removed from the sender, remove the rubber RTV seal placed over the center access hole in the end of the sensor. Insert a small standard (flat) blade screwdriver into the hole and gently adust the calibration screw. Tightening the screw will increase the oil pressure necessary to activate the switch. Loosening the screw will decrease the necessary pressure. Do not loosen the screw too far or the assembly may come apart.

The sender cannot be easily calibrated without dissassembling the unit. The gauge cluster needle may be removed and adjusted, or resistors may be added to the circuit. Those are really the only practical methods that do not risk damaging the sender.
ps262 sender calibration

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