Command reference

This is the complete list of what obd-diag may send to the adapter, with page and verbatim quote from the ELM327 datasheet (ELM327DSJ, firmware v2.1; page numbers according to the footer “N of 94”). Everything else is rejected before sending (Safety concept).

The tables are generated from tests/fixtures/command_spec.yaml when the documentation is built. The tests check the same file against the allowlist in the code (tests/verification/test_command_spec.py, exhaustively over all hex commands) and against every command sent in any test. So the list here can deviate neither from the code nor from the tests.

Commands are written as they appear on the line: upper case, no spaces, followed by a CR. Regular expressions (01[0-9A-F]{2}) stand for a group of commands, e.g. 010C.

Allowed commands

Command	Meaning	to the vehicle	writes	Source	Quote
ATZ	reset the adapter completely (as if power were switched off and on again)	no	no	datasheet p. 28	“complete reset as if power were cycled off and then on again”
ATE0	echo of received characters off	no	no	datasheet p. 17	“These commands control whether or not the characters received on the RS232 port are echoed (retransmitted) back to the host computer.”
ATL0	no linefeed after CR	no	no	datasheet p. 20	“for AT L0, they will be off.”
ATS0	no spaces in the responses	no	no	datasheet p. 24	“These commands control whether or not space characters are inserted in the ECU response.”
ATH0	hide headers in the responses	no	no	datasheet p. 18	“These commands control whether or not the additional (header) bytes of information are shown in the responses from the vehicle.”
ATH1	show headers in the responses (assignment per control unit)	no	no	datasheet p. 18	“may be of interest (especially if you receive multiple responses and wish to determine what modules they were from).”
ATSP0	search the protocol automatically (search only starts with the next OBD request)	no	no	datasheet p. 26	“the AT SP0 command sets the protocol to 0, but does not perform a write to EEPROM.”
ATRV	measure the voltage at pin 2 (battery voltage)	no	no	datasheet p. 24	“This initiates the reading of the voltage present at pin 2”
ATDP	report the current protocol as text	no	no	datasheet p. 17	“The DP command is a convenient means of asking what protocol the IC is currently set to”
ATDPN	report the current protocol as a number	no	no	datasheet p. 17	“it returns a number which represents the current protocol.”
ATI	report the adapter’s identification and firmware version	no	no	datasheet p. 18	“Issuing this command causes the chip to identify itself, by printing the startup product ID string”
AT@1	report the adapter’s device description	no	no	datasheet p. 28	“This command displays the device description string.”
ATPPS	show the summary of the programmable parameters (read only, since v1.1)	no	no	datasheet p. 23	“The complete range of current Programmable Parameters are displayed with this command”
ATIGN	read the level at the ignition input (pin 15) (since v1.4)	no	no	datasheet p. 19	“This command reads the signal level at pin 15.”
ATRD	read the byte in the user memory (since v1.4)	no	no	datasheet p. 24	“The byte value stored with the SD command is retrieved with this command.”
ATAMC	show the activity monitor count (since v2.0)	no	no	datasheet p. 12	“This count then represents the time since activity was last detected”
01[0-9A-F]{2}	Service $01: read the current value of a PID (also 00/20/40 … supported PIDs)	yes	no	datasheet p. 31	“01 - show current data”
02[0-9A-F]{2}00	Service $02: read the freeze frame, PID and frame number 00	yes	no	datasheet p. 31	“02 - show freeze frame data”
02[0-9A-F]{2}	Service $02 without frame number: fallback, only if 020200 is rejected	yes	no	datasheet p. 31	“02 - show freeze frame data”
03	Service $03: read stored trouble codes	yes	no	datasheet p. 34	“request the actual trouble codes with a mode 03 request (there is no PID needed)”
07	Service $07: read pending trouble codes	yes	no	datasheet p. 31	“07 - show ‘pending’ trouble codes”
0A	Service $0A: read permanent trouble codes	yes	no	datasheet p. 31	“0A - request permanent trouble codes”
0902	Service $09, InfoType 02: read the VIN (without response count)	yes	no	datasheet p. 32	“It is obtained with mode 09, PID 02, and should be requested with: >09 02”
0900	Service $09, InfoType 00: supported InfoTypes 01 to 20	yes	no	datasheet p. 31	“09 - request vehicle information”
0904	Service $09, InfoType 04: calibration IDs (software version) per control unit	yes	no	datasheet p. 43	“ask the vehicle for the Calibration ID (09 04)”
0906	Service $09, InfoType 06: calibration verification numbers (CVN) per control unit	yes	no	datasheet p. 31	“09 - request vehicle information”
0908	Service $09, InfoType 08: monitoring counters (in-use performance), spark ignition	yes	no	datasheet p. 31	“09 - request vehicle information”
090A	Service $09, InfoType 0A: name of the control unit	yes	no	datasheet p. 31	“09 - request vehicle information”
090B	Service $09, InfoType 0B: monitoring counters (in-use performance), compression ignition	yes	no	datasheet p. 31	“09 - request vehicle information”
06[0-9A-F]{2}	Service $06: self-diagnosis test results per monitor ID (00/20/… supported MIDs)	yes	no	datasheet p. 31	“06 - test results, non-continuously monitored”
04	Service $04: clear trouble codes, freeze frame and test results (only in allow_clear)	yes	yes	datasheet p. 35	“the SAE specifies that scan tools must verify that a mode 04 is intended (‘Are you sure?’) before actually sending it to the vehicle”

Forbidden examples

The allowlist rejects these commands; the tests check that none of them is ever sent.

Command	Why forbidden	Source	Quote
(CR only)	a lone CR repeats the last command (after 04 that would mean clearing again)	datasheet p. 9	“the ability to repeat any command (AT or OBD) when only a single carriage return character is received.”
08	Service $08 controls components in the vehicle	datasheet p. 31	“08 - special control mode”
080100	Service $08 with test ID	datasheet p. 31	“08 - special control mode”
09021	wrong response count in the VIN request	datasheet p. 32	“If you should mistakenly send 09 02 1, you might cause problems.”
ATSP6	writes to the adapter’s EEPROM immediately	datasheet p. 36	“The Set Protocol commands cause an immediate write to the internal EEPROM”
ATSP00	writes 0 to the adapter’s EEPROM	datasheet p. 26	“if you must write 0 to the EEPROM, use command AT SP 00”
ATPP0CSV00	permanently changes a programmable parameter (here the baud rate)	datasheet p. 23	“PP hh SV yy [ Prog. Param. hh: Set the Value to yy ]”
ATSH7E0	sets the header, i.e. addresses a single control unit instead of the OBD functional address	datasheet p. 25	“particularly if experimenting with physical addressing”
ATMA	monitors the bus, closes the current protocol	datasheet p. 21	“This command places the ELM327 into a bus monitoring mode”
ATLP	puts the adapter into low power mode	datasheet p. 20	“This command causes the ELM327 to shut off all but ‘essential services’”
ATD	resets everything to defaults and can close the running session	datasheet p. 49	“the ELM327 will close the current session and then change the protocol to the default one”
ATSD00	writes a byte to the adapter’s non-volatile user memory	datasheet p. 24	“The ELM327 is able to save one byte of information for you in a special nonvolatile memory location”
AT@3OBDDIAG00000	writes the device identifier, which can only be done once	datasheet p. 28	“once written to memory, they can not be changed (ie you may only use the @3 command one time)”