During normal vehicle operation, oil is vital to ensures leak tightness between the combustion chamber and the crankcase. The oil pressure indicator shows how well this is being done.

An unusual drop in oil pressure can result from either lower engine oil viscosity due to dilution by fuel (injector problem or use at low load) ; too little oil in the lubrication system (due to an oil leak, excess oil consumption, or failure of the oil circulation pump) ; or even mechanical part wear.