New generation Smart Oxygen Sensor Simulator.

A popular modification for many performance enthusiasts is to replace or remove catalytic converter to free up horsepower and increase engine output. OBD-II equipped vehicles have from two to four oxygen sensors. Upstream sensors (before catalytic converters) are used by fuel management system (vehicle ECU) to maintain proper fuel ratio. Downstream sensors (after catalytic converters) are used to monitor converter efficiency to process exhaust gases. Even small catalytic converter efficiency drop (5%) causes ECU to illuminate Check Engine sign. That functionality is mandated by the government regulations. When catalytic converters are replaced with high flow models or just purely eliminated ECU sense that by reading downstream oxygen sensor signal. It results in P0420 or P0430 fault codes stored in the ECU. Vehicle with CEL (Check Engine Light) cannot pass yearly inspection and it is just annoying to drive the car with CEL on. It also prevents operator from being alerted about any other faults that would normally cause Check Engine sign.

One of the common solution is to add oxygen sensor simulator to the downstream sensor in order to simulate signal coming from the sensor with properly functioning catalytic converter. That approach allows user to operate vehicle with high flow converters or without them and at the same time keep the CEL off.

As the vehicle ECU OBD-II systems became more advanced, manufacturers came up with better and more accurate methods of measuring efficiency and determine when converter is out of specification. Generic O2 simulator produces cycling output signal from 0.3 to 0.6 volts which worked on most cars at first when catalytic converter efficiency checks were introduced to the vehicle's ECU in 1996. Though above approach worked at first on many cars it never worked on cars like Volkswagen and Audi.

From introduction of mandatory OBD-II in 1996 manufactures mostly used Zirconia type oxygen sensors for upstream and downstream locations. In 1999 Toyota started to use Air Fuel Ratio oxygen sensors as upstream sensor which provided more accurate reading and resulted in better fuel economy. Government mandated minimum MPG fuel consumption and race between manufactures to build cars with better fuel economy lead to the development of Lambda sensors also known as wide band oxygen sensors.

With more accurate fuel ratio measurements, methods of monitoring catalytic converter efficiency were also improved. In modern vehicle ECU performs intrusive tests by intentionally lowering and increasing air fuel ratio to test catalytic converter efficiency. ECU then monitors downstream sensor response times and voltage levels relative to the upstream sensor to determine if converter efficiency is still in acceptable range.

Typical O2 sensor simulator will not work in this situation when ECU performs intrusive converter efficiency tests because voltage levels and response times are no longer in sync with upstream oxygen sensor.

Another common solution is oxygen sensor spacer. It consist of metal pipe about two inches long plugged exhaust pipe and downstream oxygen sensor. Metal pipe has a small orifice allowing exhaust gases to pass from exhaust pipe to oxygen sensor. The size of the hole is established through trial approach. Only small amount of gases enters oxygen sensor chamber so the large fluctuation of air fuel mixture are not affected sensor too much. These mechanical simulators work with mixed results. They require maintenance to clean the orifice once carbon is accumulated closing or altering its size. There is also modification of those spacers with actual small converter honeycomb cell inserted before oxygen sensor. It acts as its own catalytic converter for gases passing to the sensor. Since the exhaust gases do not flow through the sensor chamber the small converter cell never heats up to 700 degree. It never burns byproducts of combustion process and finally fails at some point.

Our previous generation O2 simulators worked by generating 0.3 to 0.6 volts cycling signal and it worked on many cars, but on cars after 2000 they had mixed results. Either only working initially or not working at all.

We started looking into the solution. We performed data logging various cars and obtaining information from manufactures on how the catalytic converter intrusive tests are performed and graded. We spent number of years building various prototypes and trying different approaches. Our goal was not to create O2 simulator for a specific car but build a device with mathematical model of the catalytic converter, so it can be applied to any car. So what we built is Smart O2 simulator which should be called “Catalytic Converter Simulator” since it takes signal from the upstream oxygen sensor and figures out what would the downstream oxygen sensor output should be if the catalytic converter would be present.

Our new generation Smart O2 simulator works on virtually all car models. It can take input from Zirconia, Tatania, Ratio and 5/6 wires wideband sensors covering all the types used by car manufactures.

Smart O2 simulator connects between one upstream and one downstream sensor. Cars with two downstream oxygen sensors would require two O2 simulators. Besides connecting two wires to upstream and two wires to downstream sensors, separate connection would need to be made to power (ground and +12v source).

O2 simulator has monitoring LEDs for inbound signal from upstream oxygen sensor and output signal for downstream sensor. Monitoring upstream oxygen sensor LEDs helps to quickly troubleshoot connection to the sensor, making sure connections is properly done and sensor type is correctly set.

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