Your engine's oil provides the vital function of lubricating the engine's moving parts. Without adequate oil pressure, the engine would not get the oil it needs to function properly. The engine is equipped with a sending unit or switch, that monitors the amount of oil pressure the oil pump is producing and sending through the system. If the oil gauge stops working, but the oil seems to be flowing correctly, the problem is likely a faulty oil pressure sending unit. Once you locate it, you can change it in just a few minutes.
Locate the oil pressure sending unit. This is a cylindrical component with an attached wiring harness that plugs into the engine. On four-cylinder 4Runners, the sending unit is located in the engine compartment, towards the passenger's side front of the engine. On six-cylinder engines, the oil pressure sending unit is under the engine, on the driver's side next to the oil filter.
Disconnect the sending unit wiring harness. The connection will attach directly to the rear of the sending unit. Pull the wire connector off the sending unit.
Place a socket over the sending unit and use a socket wrench to rotate the sending unit counterclockwise to loosen it. Continue to remove the unit by hand. Once removed, a small amount of oil may leak from the empty socket.
Clean the area around the socket and insert the new sending unit. Use the socket to tighten the unit. Re-attach the wiring connector.
Start the vehicle and watch the oil gauge. It should now function. If it still isn't working, the problem is probably with the gauge itself.
