Checklist v4: step 31, each wheel by hand on stands; DECODE-3: 449 bytes 0, 1, 3 as climate-control sensor candidates

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz
2026-10-15 22:30:40 +09:00
parent c31af2d5e3
commit 15c7d6ce84
3 changed files with 56 additions and 4 deletions
@@ -1,7 +1,7 @@
 ---
 type: plan
 status: ready
-updated: 2026-10-14
+updated: 2026-10-15
 ---
 # Z27AG decoding captures: what to do in the car

@@ -59,7 +59,9 @@ recorder refuses marks with "no session" otherwise); engine off, doors shut.
 - **On jack stands** (23–26, since v2): front wheels up, rears chocked, handbrake
  off. Unpowered steering; speedometer readings held in 2nd and 3rd (fronts turn,
  rears stay still, which tells the wheels apart); braking from speed with vacuum
-  assist; reverse. Stands replace the driving speeds where a drive is not practical.
+  assist; reverse. Stands replace the driving speeds where a drive is not practical. Step 31
+  (since v4, kept in this section, numbered after the IMU steps so earlier numbers stay): each
+  wheel spun by hand, the other front held still; the rears only if they are raised too.
 - **IMU calibration** (27–30, since v3): once the IMU is fixed in its final place. Level
  twice on the same spot, facing one way and then turned round (a rough 180° is fine:
  the ground's slope reverses and cancels, the mounting's tilt does not); then three
@@ -67,7 +69,7 @@ recorder refuses marks with "no session" otherwise); engine off, doors shut.
  which kind of stretch it is). Any session holds raw IMU samples (`imu.bin`), so
  these can go in their own short session or with anything else.

-Version 3 (2026-10-14) adds the IMU calibration section. Version 2 (2026-10-13) adds the stands section and writes down the conditions the
+Version 4 (2026-10-15) adds step 31, one wheel at a time by hand. Version 3 (2026-10-14) adds the IMU calibration section. Version 2 (2026-10-13) adds the stands section and writes down the conditions the
 first run showed matter: engine off and handbrake on for 1–13, foot brake held for
 the handbrake step, neutral with the clutch up for the revs.

@@ -64,6 +64,32 @@ Jack stands (checklist 23–26) would still confirm this, but are no longer need
  Scale unknown: full is unlikely to be 100 or 255. A refuel gives two points (before and after,
  parked level, with the litres put in). Not registered until then.

+- **`449` bytes 0, 1, 3: climate-control temperatures, most likely raw sensor readings.** Pass 2 looked
+  for a byte that equals OBD-II intake air temperature less 40 and found none. Read the other way,
+  bytes 1 and 3 run *against* it (correlation −0.96 and −0.98 in `000007`), the way a thermistor's raw
+  reading falls as it warms. They follow it over tens of minutes, not second to second, so they are
+  other sensors that warm and cool with the air around the engine and car:
+  - **Byte 3: the A/C evaporator.** At each first switch-on of the compressor (`ac_compressor`) it climbs
+    from 115–145 to about 185 within 30–60 s, then stays there while the compressor cycles on and off
+    every 10–20 s. That is the evaporator being held just above freezing, the job its sensor exists
+    for. It keeps climbing a few counts after each switch-off, as an evaporator does while the last
+    refrigerant boils off. With the A/C off it drifts with the air (the `000007` correlation above).
+    Higher count, colder.
+  - **Byte 1: outside air, probably.** Slow; 89–91 on the afternoon of the 13th, 99–117 in the evening
+    of the 15th (higher count, colder, as byte 3). It fell from 114 to 99 over 30 minutes parked and
+    idling, and rose from 112 to 117 over 8 minutes of driving. A sensor behind the grille does this:
+    radiator heat soaks it while standing, and the airflow cools it once moving. That is why climate
+    controls filter it.
+  - **Byte 0: unclear.** 119–134, slow, unmoved by the engine starting or stopping (so not the
+    charging voltage), and its sign against the other two is not consistent. A cabin sensor is one
+    guess.
+
+  An auto climate control has these three: evaporator, outside air, cabin. The way to scale them is
+  an overnight soak: a cold start after the car has stood all night gives one reading of each with
+  everything at the outside temperature (OBD-II intake and coolant say what that is). With a
+  thermometer and the A/C steps (12, 17), it gives a second. A mid-session frame with byte 6 = 24 instead
+  of 51 (end of `000009`, engine stopping) has every byte halved or changed; left out of the above.
+
 ## Notes on the recording

 - `000012` is a 25-second parked session in between; `000013` ends with the PEAK unplugged.