1991 Nissan Pathfinder Oil Pump Replacement Cost

Engine oil is kept in the engine oil pan on most engines, and an external oil reservoir on many high performance engines. In either case, the oil pump is responsible for pumping oil into the engine faster than the engine can use the oil. This creates a constant pressure as the oil is pushed through oil passages. The oil passages use targeted outlets to send oil to precise locations which need protection. Oil is less of a lubricant, and more of a barrier, as it prevents metal contact between internal engine components. When that barrier is weak, metal contact will occur at an increasing rate, relative to the rate of oil pressure degradation. The barrier the oil creates is weakened or completely compromised without oil pressure. Oil pressure forces oil into the tight areas as fast as the oil is used. This means, when the oil pump fails, engine components will run out of oil, and damage will occur.

Low oil pressure can be caused by using the incorrect type of engine oil. Be sure to check with your owners manual to ascertain the correct type for your engine and climate.

When the engine oil pump fails, the fuel pressure sensor will send a signal to the computer, signaling low oil pressure. This causes the engine's computer to illuminate the check engine light, and store on-board diagnostic (OBD) trouble codes which reflect the oil pressure readings at the sensor. Also, the engine may be placed in reduced power mode for engine protection, but in most cases, the engine will stall, and fail to restart.

When the engine oil pump fails, the vehicle can not be driven. The engine may restart if it was turned off before damage was done, but will only run for a moment before the engine fails completely. No matter how much oil is in an engine, the engine cannot run without the oil pump creating pressure.

Engine oil pumps may fail after a few thousand miles, but most often they last the lifetime of the vehicle. Most vehicles will never have an issue with the oil pump, and changing engine oil and engine oil filter on time will help prevent premature failure.

When diagnosing a possible loss of oil pressure, the technician will check the oil level first, then the engine will be inspected for engine oil leaks. This is because running low on oil can cause loss of oil pressure, and oil starvation issues. If the oil is full, and there are no leaks, the technician will connect to the vehicle with a computerized scanner to read sensor data, and compare that to actual conditions. Before the technician can suspect any mechanical failure, or start the engine, the engine oil pressure sensor must be proven to function properly. The technician will test the oil pressure sensor and associated electrical circuit, and determine if the sensor should be replaced. If the sensor is reporting correctly, the technician will suspect the engine oil pump, which necessitates removal of the oil pan, and physical inspection.

Low oil pressure can be caused by a plugged oil pick-up screen or leaking seals in the engine. It is important that these items are inspected before replacing the oil pump.

After a diagnosis is made, if the oil pressure sensor is faulty, it will be resealed (if required) and replaced. If the engine oil pump is suspected, the engine oil pan must be removed. The oil will be drained, and all obstructions must be removed. The oil pan is unbolted, the seal is broken, and the oil pump is confirmed faulty. The new oil pump will be installed according to manufacturer specification, and the oil pan will be replaced. Once all obstructions are replaced, the engine oil is filled, and the engine is turned with the starter without ignition power. If oil pressure builds, the engine can be started and tested.

The oil pressure should be checked before condemning an oil pump. A good quality repair shop will perform an oil pressure check and record the readings on the repair order.