What are the meanings of the returned values for OBD2 Mode 1 PID 12?

One source shows me

A0     Upstream of catalytic converter
A1     Downstream of catalytic converter
A2     From the outside atmosphere or off
A3-A7  Always zero

Another source (wiki's PID) shows me

1   Upstream
2   Downstream of catalytic converter
4   From the outside atmosphere or off
8   Pump commanded on for diagnostics

I would like to know which one is correct and what it means when it returns a value corresponding to:

  1. Upstream of catalytic converter
  2. Downstream of catalytic converter
  3. From the outside atmosphere or off
  4. Zero?
  5. Pump commanded on for diagnostics

This information is from SAE J1979DA, June 2014, edition, hence should be considered authoritative:

PID 12 is Commanded Secondary Air Status. Expected is one return byte with the following semantics:

  • bit 0: 1 = upstream of first catalytic converter
  • bit 1: 1 = downstream of first catalytic converter inlet
  • bit 2: 1 = atmosphere / off
  • bit 3: 1 = pump commanded on for diagnostics
  • bit 4 -7: SAE-reserved, should be 0

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