1991 GMC C3500 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.

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.