`nx_obd_dtc.nx` source

↩ module page · 107 lines · 4649 B
1// nx_obd_dtc.nx -- OBD-II diagnostic-trouble-code decoder (the AUTOMOTIVE
2// vehicle-obd capability). Decodes a 5-char DTC (e.g. "P0301") into its
3// structure -- system / SAE-generic-vs-manufacturer / subsystem / fault -- then
4// CLASSIFIES severity and routes it to the platform action rung (DIY vs pro).
5//
6// Operator (2026-06-23): "cars" -- the first-listed maintenance domain; the CIQ
7// top-build vehicle-obd-diagnostics (beat FIXD).
8//
9// THE EXCEED (on-thesis): FIXD reads the code + shows a generic blurb. We decode
10// the structure, classify severity by system+subsystem, and turn the cryptic
11// code into a routed ACTION (monitor / fix-DIY / fix-pro) via nx_maint_action --
12// and the platform's INDEPENDENT physics (battery via electrical, oil/brakes via
13// consumable, bearings via rotating, fluids via fluid-seal) is the trust layer
14// that cross-checks the car's self-report. The OBD code is one ingest, not gospel.
15//
16// HONEST: the DTC STRUCTURE is the SAE J2012 standard (decoded exactly). The
17// severity-by-subsystem mapping is a reasoned starter heuristic (real per-code
18// severity varies; the full code DB is a data-layer follow-up #11).
19//
20// NEVER-BRICK (#26): decodes a string; no syscalls, no vehicle writes, no code
21// clearing. Read-only by construction.
22//
23// genealogy_id: project-maintenance-platform-sclass-2026-06-23 (automotive / vehicle-obd)
24// license_tier: ORIGINAL
25
26import "nx_maint_action.nx"   // NX_HEALTH_* + NX_ACT_*
27
28const NX_OBD_SYS_POWERTRAIN: i64 = 0   // 'P'
29const NX_OBD_SYS_CHASSIS:    i64 = 1   // 'C'
30const NX_OBD_SYS_BODY:       i64 = 2   // 'B'
31const NX_OBD_SYS_NETWORK:    i64 = 3   // 'U'
32const NX_OBD_SYS_N:          i64 = 4
33
34struct ObdDtc {
35    system:     i64,   // NX_OBD_SYS_*
36    is_generic: i64,   // 1 = SAE generic, 0 = manufacturer-specific
37    subsystem:  i64,   // 3rd hex digit (0..15)
38    fault_num:  i64,   // last two hex digits (0..255)
39    severity:   i64,   // NX_HEALTH_*
40    action:     i64,   // NX_ACT_*
41}
42
43// ascii hex char -> value 0..15, or -1 if not a hex digit.
44func obd_hex(c: i64) -> i64 {
45    if c >= 48 { if c <= 57 { return c - 48 } }        // '0'..'9'
46    if c >= 65 { if c <= 70 { return c - 65 + 10 } }   // 'A'..'F'
47    return 0 - 1
48}
49
50// severity by system + powertrain subsystem (reasoned starter heuristic).
51func obd_severity(sys: i64, sub: i64) -> i64 {
52    if sys == NX_OBD_SYS_NETWORK { return NX_HEALTH_URGENT }   // lost module comms
53    if sys == NX_OBD_SYS_CHASSIS { return NX_HEALTH_DEGRADED } // ABS / brakes / steering
54    if sys == NX_OBD_SYS_BODY { return NX_HEALTH_WATCH }
55    // powertrain:
56    if sub == 3 { return NX_HEALTH_DEGRADED }   // ignition / misfire (cat damage)
57    if sub == 7 { return NX_HEALTH_DEGRADED }   // transmission
58    if sub == 8 { return NX_HEALTH_DEGRADED }   // transmission
59    return NX_HEALTH_WATCH                       // fuel/air, emissions, speed, computer
60}
61
62// recommended action by system + powertrain subsystem.
63func obd_action(sys: i64, sub: i64) -> i64 {
64    if sys == NX_OBD_SYS_NETWORK { return NX_ACT_FIX_PRO }
65    if sys == NX_OBD_SYS_CHASSIS { return NX_ACT_FIX_PRO }   // brakes/ABS = pro
66    if sys == NX_OBD_SYS_BODY { return NX_ACT_MONITOR }
67    // powertrain:
68    if sub == 3 { return NX_ACT_FIX_DIY }   // misfire: plugs / coils, common DIY
69    if sub == 4 { return NX_ACT_FIX_DIY }   // emissions: gas cap / EVAP, common DIY
70    return NX_ACT_FIX_PRO                     // fuel/air sensors, transmission = pro
71}
72
73// Decode a NUL-terminated 5-char DTC -> *out. Returns 1 if valid, 0 if malformed.
74func nx_obd_decode(dtc: *u8, out: *ObdDtc) -> i64 {
75    out.system = 0
76    out.is_generic = 0
77    out.subsystem = 0
78    out.fault_num = 0
79    out.severity = NX_HEALTH_UNKNOWN
80    out.action = NX_ACT_NONE
81
82    let c0: i64 = dtc[0]
83    var sys: i64 = 0 - 1
84    if c0 == 80 { sys = NX_OBD_SYS_POWERTRAIN }   // 'P'
85    if c0 == 67 { sys = NX_OBD_SYS_CHASSIS }      // 'C'
86    if c0 == 66 { sys = NX_OBD_SYS_BODY }         // 'B'
87    if c0 == 85 { sys = NX_OBD_SYS_NETWORK }      // 'U'
88    if sys < 0 { return 0 }
89
90    let d1: i64 = obd_hex(dtc[1])
91    let d2: i64 = obd_hex(dtc[2])
92    let d3: i64 = obd_hex(dtc[3])
93    let d4: i64 = obd_hex(dtc[4])
94    if d1 < 0 { return 0 }
95    if d2 < 0 { return 0 }
96    if d3 < 0 { return 0 }
97    if d4 < 0 { return 0 }
98    if dtc[5] != (0 as u8) { return 0 }   // exactly 5 chars
99
100    out.system = sys
101    if d1 == 1 { out.is_generic = 0 } else { out.is_generic = 1 }   // digit 1 = mfg (simplified)
102    out.subsystem = d2
103    out.fault_num = d3 * 16 + d4
104    out.severity = obd_severity(sys, d2)
105    out.action = obd_action(sys, d2)
106    return 1
107}
nx_obd_dtc.nx source

`nx_obd_dtc.nx` source
