Realtime A/F ratio display with a DGauge

We've had a number of questions regarding A/F ratio display using our DGauge so we wanted to post some info about the factory Honda O2 sensor and OBD2.

K-Series engines and associated electrical systems utilize a wideband O2 sensor.
Most people should know this since K-Pro shows the A/F ratio.

The popular 2002~2004 RSX Type-S ECU does not support A/F ratio through diagnostics (with the exception of 2004 model year) even though the system utilizes a wideband O2 sensor. The ECU supports the O2 sensor voltage, as with many older vehicles that have narrow band O2 sensors. However, the response of the O2 sensor voltage is not the same as a narrow band sensor and can be converted to A/F ratio.

So, to get A/F ratio using the OBD2 data, you can use the DGauge and select the "AFR K20" parameter type.

Later versions of the Honda K20/K24 do support the A/F ratio through diagnostics, so no conversion is necessary.

OBD2 data update rates for the earlier K20 ECU are not speedy, but if you are only monitoring a couple of parameters, then it's plenty fast enough. Later systems, such as that in the 8th gen Civic use a much faster communication method.