I’ll take a crack at this one.

I have always ‘presumed’ it was additional data provided by Torque – representing a “Switch” in voltage level that qualifies as one count for the OBDII System’s “CATALYST MONITOR” routine.

Having said that, I must add that for purposes of this post, I have been unable to find competent documentation that tells me exactly what that level should be – a percentage, a specific voltage or what. But the OBDII system monitors the catalytic converter efficiency in storage of oxygen, and the ‘ratio’ of switching between the Front O2 sensor and the Rear O2 Sensor represents the converters efficiency. A switch ‘ratio’ between front/rear O2’s outside a pre-defined level will trigger a catalyst inefficiency DTC. The following text comes from the Motorcraft OBDII Theory of Operation Manual.

—–
Catalyst Efficiency Monitor:

The Catalyst Efficiency Monitor uses an oxygen sensor before and after the catalyst to infer the hydrocarbon
efficiency based on oxygen storage capacity of the ceria and precious metals in the washcoat. Under normal,
closed-loop fuel conditions, high efficiency catalysts have significant oxygen storage. This makes the switching
frequency of the rear HO2S very slow and reduces the amplitude of those switches as compared to the switching
frequency and amplitude of the front HO2S. As catalyst efficiency deteriorates due to thermal and/or chemical
deterioration, its ability to store oxygen declines. The post-catalyst HO2S signal begins to switch more rapidly with
increasing amplitude, approaching the switching frequency and amplitude of the pre-catalyst HO2S. The
predominant failure mode for high mileage catalysts is chemical deterioration (phosphorus deposition on the front
brick of the catalyst), not thermal deterioration.

All applications utilize an FTP-based (Federal Test Procedure) catalyst monitor. This simply means that the
catalyst monitor must run during a standard FTP emission test as opposed to the 20-second steady-state catalyst
monitor used in 1994 through some 1996 vehicles. Two slightly different versions of the catalyst monitor are used
for 2001 MY and beyond vehicles. Both versions will continue to be used in subsequent model years.

Switch Ratio Method (1996 – 2004):
In order to assess catalyst oxygen storage, the monitor counts front and rear HO2S switches during part-throttle,
closed-loop fuel conditions after the engine is warmed-up and inferred catalyst temperature is within limits. Front
switches are accumulated in up to nine different air mass regions or cells although 3 air mass regions is typical.
Rear switches are counted in a single cell for all air mass regions. When the required number of front switches has
accumulated in each cell (air mass region), the total number of rear switches is divided by the total number of front
switches to compute a switch ratio. A switch ratio near 0.0 indicates high oxygen storage capacity, hence high HC
efficiency. A switch ratio near 1.0 indicates low oxygen storage capacity, hence low HC efficiency. If the actual
switch ratio exceeds the threshold switch ratio, the catalyst is considered failed.
——- etc. etc.

If I have this all wrong, I hope someone who knows more will chime in or completely correct my theory.

————-

54371019

Thanks for the replies trying to explain. I think i will still be wondering though. Sounds like advanced info being supplied to the viewer. Funny that a five dollar app is giving me advanced info when my 1,000 dollar scanner does not.