P0178 MERCEDES-BENZ – Fuel Composition Sensor Circuit Low Input

P0178 MERCEDES-BENZ Possible Symptoms

Engine Light ON (or Service Engine Soon Warning Light)

P0178 MERCEDES-BENZ Possible Causes

Flexible Fuel (FF) sensor to Vehicle Power (VPWR) circuit harness open or shorted,FF to VPWR circuit poor electrical connection,Open in FF sensor signal circuit,Short to ground in FF sensor signal circuit,Fuel contamination,Short to VPWR in FF sensor batte

P0178 MERCEDES-BENZ Description

Fuel Composition Sensors are used to determine the amount of ethanol alcohol in the gasoline. Normally, a gasoline engine should not have more than 10% ethanol alcohol in the fuel for proper operation. Some vehicles have a Flexible Fuel (FF) system on them that allow them to run on up to 85% ethanol alcohol in the fuel. The fuel composition sensor sends a frequency modulated signal to the engine controller which is proportional to the alcohol content of the fuel. The injector pulse width and the ignition timing are modified for the increased alcohol content. It takes almost twice the amount of alcohol compared to gasoline to produce the same power.