Tightening emissions regulations are driving increasing focus on both equipment and measurement capabilities in the test cell environment. Customer expectations are therefore rising with respect to data uncertainty. Key critical test cell parameters such as load, fuel rate, air flow and emission measurements are more heavily under scrutiny and require real time methods of verification over and above the traditional test cell calibration in 40CFR1065 regulation. The objective of this paper is to develop a system to use a carbon dioxide (CO2) based balance error and an oxygen (O2) based balance error for diagnosing the main measurement system error in the test cell such as fuel rate meter, air flow meter, emission sample line, pressure transducer and thermocouples. The general combustion equation is used to set up the balance equations with assumptions. To validate the air fuel ratio balance model an experimental investigation was carried out for D2 5 mode and C1 8 mode cycle test. Once the test was carried out, the AFR_O2 and the AFR_CO2 were calculated in the developed analysis model with a pass/fail threshold of ±3%. Then the sensitivity response of measurement system such as fuel meter, air flow meter, pipe boost pressure, atmospheric pressure, CO2 analyser and O2 analyser were investigated. Finally a user guide sheet has been developed based on sensitivity analysis.