Live data

Live data queries current values round by round (mode 01) and shows them, optionally recording them as CSV.

obd-diag live --port /dev/ttyUSB0 --list                      # supported values
obd-diag live --port /dev/ttyUSB0                             # usual values, Ctrl+C stops
obd-diag live --port /dev/ttyUSB0 --pids rpm,speed,fuel_rail_pressure --interval 0.5
obd-diag live --port /dev/ttyUSB0 --duration 60 --record      # record 60 s as CSV

Time (s)  Engine speed (rpm)  Speed (km/h)  Coolant temperature (°C)  …  Voltage (V)
     0.0                1726            50                        86  …         14.1
     1.0                1731            51                        86  …         14.1

Warning

While driving, only a passenger should operate this.

Which values

140 values from 87 mode 01 PIDs according to SAE J1979, among them engine speed, speed, temperatures, load, air flow, manifold, rail and boost pressure, AdBlue, EGR, fuel trim, oxygen sensors 1–8, torque, fuel level, fuel rate and odometer. The complete list with key, formula and value range is in PID formulas.

  • Only values the vehicle reports as supported are requested (0100, 0120 … across all control units). --list shows them with their key.

  • Without --pids: engine speed, speed, coolant temperature, load, intake air temperature and control module voltage, as far as supported.

  • If one PID returns several values (sensor voltage and trim), it is queried only once per round.

  • The sensors are numbered 1–8 in PID order. Which bank and position that is, is defined by the vehicle (PID 13 or 1D).

  • Not included are PIDs with a status byte whose structure is not unambiguous in free sources, among them boost pressure (70) and particulate filter (7A–7C).

One round

  • Each selected value is read once. If one cannot be read, “-” is shown (an empty cell in the CSV) and the query carries on.

  • The battery voltage (ATRV) is read every tenth round. If the adapter shows less than 11.8 V, it is cross-checked with the control module voltage (PID 42): many adapters measure a few tenths of a volt too little behind a protection diode. If that is also below (or missing), values are only queried every 5 s to protect the battery. While throttled, the voltage is measured every round; once it is high enough again (engine started), polling continues at the normal rate right away.

  • If the adapter reports a bus error for every value for three rounds (e.g. ignition off), the query ends with an error message. NO DATA, ? and rejections do not count as bus errors.

  • Only 01xx and ATRV are sent, plus ATH1/ATH0 (headers on and off) when multi-frame responses of several control modules get mixed up.

Warning thresholds

If a value is below its lower or above its upper threshold, it is marked with ! in the table and a note reports when the warning starts and ends; in the window the tile turns red and a bar names the value. Defaults (rough guide values that do not trigger in normal operation; what is normal for your own car is in its documentation):

Value

Key

Warning

Coolant temperature

coolant_temp

above 115 °C

Engine oil temperature

oil_temp

above 130 °C

Control module voltage

control_voltage

below 11.8 V, above 15.5 V

Battery voltage (ATRV)

voltage

below 11.8 V, above 15.5 V

 
obd-diag live --alarm coolant_temp=:105 --alarm rpm=:4500   # set upper limits
obd-diag live --alarm voltage=12.2: --alarm oil_temp=:       # lower limit; warning off
obd-diag live --no-alarms --alarm speed=:130                 # only this one threshold

--alarm KEY=LOW:HIGH replaces the default for that value; an empty side means no limit, comma or point are both accepted as decimal separator. In the window, “Warning thresholds …” sets them per value; they are saved and apply from the next start. Only the values that are read anyway are checked; nothing extra is sent.

Recording

--record writes a CSV under ~/.local/share/obd-diag/recordings/ (live-YYYYMMDD-HHMMSS.csv) or to the given file, which is never overwritten. The format follows the language (Language): UTF-8 with BOM; in English , as separator and a decimal point, in German ; and a decimal comma. First column Time (s), then Name (unit) per value, Battery voltage (V) and last Warnings (thresholds exceeded in that round as text, several separated by |, otherwise empty). Every row is written immediately, so an abort loses nothing.