Commanded secondary air status
Last reviewed 2026-08-31
Mode 01 · PID 12 (decimal 18)
Description
Secondary air injection command: upstream, downstream of catalyst, atmosphere/off, or pump on for diagnostics.
- PID number
- 12 · 18
- Unit
- —
- Range
- —
- Data bytes
- 1
- Formula
- Enumerated (upstream / downstream / off)
Allowed values
| Value | Meaning |
|---|---|
| 1 | Upstream |
| 2 | Downstream of catalytic converter |
| 4 | From outside atmosphere or off |
| 8 | Pump commanded on for diagnostics |
- Also valid as Mode 02 freeze-frame data (same PID number, snapshot at last DTC).
- Bit-encoded or enumerated — not a single scaled physical value.
Defined by SAE J1979 / ISO 15031-5. Public index — not a substitute for the paid SAE document.
Sources
Provenance for this page. Official standards outrank community notes. See the confidence policy.
Official standard · high trust
SAE J1979 / ISO 15031-5 Mode 01 PID formulas (public index)
J1979 public PID index: 01 12