Documentation
¶
Overview ¶
Package obd2 decodes OBD-II / SAE J1979 Mode-01 ("show current data") responses into engineering values — turning the raw measurement bytes of a diagnostic response into RPM, speed, coolant temperature, MAF, etc. via the standard per-PID formulas.
Wrap-vs-native judgement ¶
Native. The J1979 Mode-01 PID set and its conversion formulas are public, exact, and transport-independent (the same A/B-byte formulas apply whether the response arrived over CAN/ISO 15765, J1850 VPW/PWM, or ISO 9141) — documented in SAE J1979 and reproduced identically by python-OBD, ELM327-based tools, and the widely-cited OBD-II PID tables. Decoding is a static table of (name, unit, byte-count, formula) entries; no hardware, no vendor SDK, no probing. The existing internal/j1850 decoder names the PID but stops at the raw payload bytes ("Engine RPM" + payload_hex) — this computes the value those bytes encode, and works for any transport since the caller supplies the already-extracted Mode-01 payload.
No confidently-wrong output ¶
Only PIDs whose formula is in the table are given a value; an unknown PID, or a known PID with too few data bytes, is surfaced with its raw hex (and name when known) plus a note — never a guessed number. Manufacturer- specific PIDs and the bitmask/string PIDs (e.g. 0x00/0x20 "PIDs supported", 0x03 fuel status, VIN) are intentionally left to the raw bytes.
Index ¶
Constants ¶
const Mode01Response = 0x41
Mode01Response is the service byte of a Mode-01 ("current data") response — the request mode 0x01 plus 0x40.
Variables ¶
This section is empty.
Functions ¶
This section is empty.
Types ¶
type DTC ¶ added in v0.396.0
type DTC struct {
Code string `json:"code"` // canonical form, e.g. "P0143"
Category string `json:"category"` // Powertrain | Chassis | Body | Network
Raw string `json:"raw"` // the 2 source bytes as hex
Generic bool `json:"generic"` // SAE/ISO-controlled (first digit 0)
ManufacturerSpecific bool `json:"manufacturer_specific"` // manufacturer-controlled (first digit 1)
}
DTC is one decoded Diagnostic Trouble Code.
func DecodeDTC ¶ added in v0.396.0
DecodeDTC unpacks a 2-byte Diagnostic Trouble Code into its canonical J2012 form. Byte A's top two bits select the category letter (P/C/B/U), the next two bits are the first digit (0-3), A's low nibble is the second digit, and byte B's two nibbles are the third and fourth digits.
A = 0x01, B = 0x43 -> "P0143" A = 0x04, B = 0x20 -> "P0420"
type DTCResponse ¶ added in v0.396.0
type DTCResponse struct {
Mode int `json:"mode,omitempty"` // 0x43 / 0x47 / 0x4A when a service byte was present
ModeName string `json:"mode_name,omitempty"` // human service name
Count int `json:"count"` // number of trouble codes decoded
DTCs []DTC `json:"dtcs"`
Notes []string `json:"notes,omitempty"`
}
DTCResponse is the decoded view of a stored/pending/permanent DTC response.
func DecodeDTCResponse ¶ added in v0.396.0
func DecodeDTCResponse(hexStr string) (*DTCResponse, error)
DecodeDTCResponse parses a Mode-03/07/0A DTC response into its trouble codes. The input may be the response payload prefixed with the service byte (0x43 / 0x47 / 0x4A) or the bare stream of 2-byte DTCs. All-zero pairs (0x0000) are padding and are skipped. Separators and a 0x prefix are tolerated.
type Reading ¶
type Reading struct {
PID int `json:"pid"`
PIDHex string `json:"pid_hex"`
Name string `json:"name"`
RawHex string `json:"raw_hex"`
Value *float64 `json:"value,omitempty"`
Unit string `json:"unit,omitempty"`
Formula string `json:"formula,omitempty"`
Note string `json:"note,omitempty"`
}
Reading is the decoded view of one Mode-01 PID.
func DecodePID ¶
DecodePID decodes one Mode-01 PID from its measurement bytes, computing the engineering value via the J1979 formula when the PID and byte count are known.
func DecodeResponse ¶
DecodeResponse parses a Mode-01 response payload — the service byte (0x41) + PID + measurement bytes — and decodes the PID. A request byte (0x01) is also accepted (named, no value, since a request carries no measurement). Separators and a 0x prefix are tolerated.
Source Files