# Device-enable flags (SAI / O2 / lambda) — validated

## How they were found

Both stock reference maps (20187, 20188) have SAI and O2 **active**, so diffing
them can't reveal the delete flags. The confirmation came from a community map
that explicitly disables them:

`20188Map2009AIRBOXBONNY.hex` — "Bonneville, aftermarket exhaust, mechanical
odometer, NO AIR BOX, K&N, British Custom mufflers, **NO SAI, NO O² SENSORS**".
Same base as stock 20188, so the diff isolates the deletes.

Diff (flat ROM) of that map vs stock 20188 = 0.36%, split into:
- the fuel tables (airbox/K&N enrichment — expected), and
- a small cluster in the device-config region at **0x53801…0x53819**.

## The flags

They are a **byte-boolean array** at flat-ROM `base + fe[33]` (= `0x50000 + 0x3801
= 0x53801`), one byte per device, **1 = enabled, 0 = disabled**.

The delete map changed exactly three bytes from 1 → 0:

| Flat-ROM offset | Stock | Deleted | Device |
|---|---|---|---|
| `0x53801` | 1 | 0 | **SAI** (Secondary Air Injection) |
| `0x53818` | 1 | 0 | **O2 sensor** |
| `0x53819` | 1 | 0 | **O2 sensor (2)** |

SAI is the first flag in the array; the two O2 sensors are the last two —
consistent with the `Devices` resource order (SAI = index 0; O2 Sensor / O2
Sensor (2)). The three-byte change matching "NO SAI, NO O²" is unambiguous.

To disable a device: set its byte to `0`. (The `0x5369C`/`0x536AB` bytes that
also changed are idle/open-loop trim that comes with removing the O2 feedback,
not device-enable flags.)

## Editing / export

The downloaded `.hex` format's integrity is the `dc` stream cipher + the unpack
directory; the `caXX` bytes in the header/tail are map-ID metadata, **not** a
calibration checksum. So a device toggle = flip the byte in the flat ROM, re-pack
to the decoded layout, and `dc`-encode back to `.hex`. (The separate *ECU flash*
checksum is computed at flash time and is out of scope for the read/edit tool.)

## Confidence

- Flag **locations** (0x53801 / 0x53818 / 0x53819) and semantics (1/0): **validated**
  against a real NO-SAI-NO-O2 map.
- SAI-vs-O2 **labeling** of the three bytes: strong (order + delete semantics);
  final SAI-only-vs-O2-only separation would need a single-delete reference map or
  a DTC/bench check.