What does it mean?
OBD II fault code P046C is a generic trouble code that is defined as, P046C –“Exhaust Gas Recirculation Sensor “A” Circuit Range/Performance” or sometimes as P046C – “Exhaust Gas Recirculation (EGR) Position Sensor Performance”, and is set when the PCM (Powertrain Control Module) detects an implausible or unexpected input from the exhaust gas recirculation valve’s position sensor.
The purpose of exhaust gas recirculation systems is to divert some exhaust gas from the exhaust systems and then to inject small metered amounts of exhaust gas into the cylinders to quench or reduce the combustion temperature to below the point where oxygen and nitrogen combine.
At or above combustion temperatures of 2200 deg F, oxygen and nitrogen combine to form NOx, a toxic and extremely harmful substance that is implicated not only in the formation of urban smog and acid rain but also in several serious human health issues. These include but are not limited to, potentially life-threatening respiratory problems, several pollution-induced cancers; several types of heart diseases, sudden heart attacks, and strokes in susceptible individuals.
So in a fully functional exhaust gas recirculation system, the PCM will command the exhaust gas recirculation valve to open under some operating conditions to introduce some exhaust gas into the engine, and as a general rule, the introduced exhaust gas will prevent the formation of NOx.
However, since the PCM cannot monitor or measure the volume of exhaust gas that passes into the engine through the valve directly, it uses the position of the valve pintle as a guide to infer the volume of exhaust gas that passes through the valve. As a practical matter, the position sensor monitors the position of the valve pintle in a range of possible movements from fully closed, to fully open.
If we assume that both the exhaust gas recirculation valve and its integrated position sensor work as both designed and expected and the valve is 50 percent open, the signal voltage from the position sensor will indicate to the PCM that the valve is indeed 50 percent open.
However, given the corrosive nature of exhaust gas, and the fact that exhaust gas contains high concentrations of unburned fuel and oil residues, it is not surprising that most exhaust gas recirculation valves experience a build-up of carbon and soot deposits. In severe cases, such accumulations of carbon can block a valve completely, but in most cases, lighter carbon deposits can impede or hinder the free movement of the valve pintle.
For example, carbon deposits could prevent an exhaust valve recirculation valve from either opening or closing completely, or from moving at all. This means that if the PCM commands the valve open by any amount, the PCM will expect to see a signal voltage from the valve’s position sensor that corresponds to the commanded opening.
Thus, if the input from the position sensor deviates from the input the PCM expects to see by a specified amount, the PCM will interpret the input it receives as implausible/unexpected. If the above scenario happens, the PCM will recognize that it cannot control the exhaust gas recirculation system effectively, and it will set code P0232 as a result.
Note that since a failure of this kind has the potential to increase harmful exhaust emissions, the PCM will also illuminate a warning light that may or may not flash, depending on the vehicle’s make and model.