Typically the combustion in an internal combustion engine is open-loop controlled. The introduction of a cylinder pressure sensor opens the possibility to introduce a virtual combustion sensor. This virtual sensor is a possible enabler for closed-loop combustion control and thus the possibility to counteract effects as engine part to part variation, component ageing and fuel quality diversity. The extent to which these effects can be counteracted is determined by the detection limits of the virtual combustion sensor. To determine the limitation of the virtual combustion sensor a virtual combustion sensor system was implemented based on a one-zone heat-release analysis, including signal processing of the pressure sensor input. Typical error sources in a heavy-duty engine were identified and quantified. The virtual combustion sensor system was presented with flawed signals and the sensors sensitivities to the errors were quantified. It could be concluded that the sensor signals are dependent on the choice of heat-release model and specific heat ratio model. Crank angle phasing was found to have a significant impact on estimation performance, stressing the importance of accounting for crank angle sensor – crankshaft offset and crankshaft torsion. The determining of the late crank angle burned (i.e. crank angle where 90% burned) was found to be more sensitive to errors in the data supplied to the virtual combustion sensor than the earlier crank angle burned (i.e. crank angle where 10% and 50% burned) indicating that the crank angle where 10% and 50% burned are more robust control parameters than the crank angle where 90% burned or the combustion duration.