Oxygen sensors are the primary component for measuring A/F ratio. Most vehicles have conventional sensors which have a range of 0 to about 1.1 volts. These sensors have a somewhat slow response time and narrow band or range. The ECU uses the data from this sensor to determine if the mixture is rich or lean. In contrast, a wide-band O2 sensor has a wider range, as it's name implies and is very accurate at determining how rich or lean the mixture is. This type of sensor usually has 5 wires, some integrated electronics and the input into the ECU is either a 0 to 5 volt range or a -128 to +128 milliamp range. Some newer vehicles such as BMW and VW/Audi use this type of sensor. An interesting departure from the standard wideband sensor is a Denso 4-wire sensor used in some Honda vehicles with K-series engines. This O2 sensor does not have integrated electronics. It can be found on the Acura RSX, TSX, Honda Element and 2002 - 2005 Honda Civic Si. Brockway Engineering includes a conversion to A/F ratio for these vehicles in our OBD2 Gauges because the ECU does not report A/F ratio data as it is supposed to. The OBD2 spec states that vehicles with wideband sensors must output the equivalence ratio (lambda), which can then be converted to A/F ratio. Stricter emission regulations are driving the OEM's to use more accurate fuel control, requiring the use of wide-band O2 sensors.