https://docs.emtronaustralia.com.au/engine-management/functions/lambda-control/exhaust-back-pressure/index.htmlWideband Lambda sensors primarily count oxygen atom numbers through measuring the oxygen ion current within the sensors pump cell. The exhaust gas pressure affects this oxygen ion current – more pressure means more atoms per unit volume and a higher pump current at the same Lambda.i.e will cause the sensor to read farther from stoichiometric A rich reading will appear richer than it really is. A lean reading will appear leaner than it really This predominantly becomes an issue in Turbocharged applications. This is the main reason you should position the sensor after the turbo where exhaust back-pressure is lowest.Hugoen-us