ELM327 Commands: AT Command List, PIDs and a Terminal Walkthrough

You need three things: an adapter that shows up as a serial port, a terminal program, and the right speed setting.

1. Connect. A USB cable appears as a COM port once its CH340 or FTDI driver is installed. A Classic Bluetooth adapter paired with Windows also creates a COM port. On Android, a Bluetooth terminal app does the same job.
2. Open a terminal. PuTTY, Tera Term or any serial terminal works on Windows.
3. Set the speed. Many adapters default to 38400 baud and older ones to 9600, with 8 data bits, no parity and one stop bit. Faster models vary, so check the manual.
4. Turn the ignition on, then type ATZ and press Enter.

A healthy adapter answers with its version string and then a > prompt. The prompt is the adapter saying it is ready for the next command. Garbled characters instead mean the speed is wrong, so try the other common rate before suspecting the adapter.

>ATZ
ELM327 v1.5

>

ATZ      reset the adapter
ATE0     echo off
ATL0     linefeeds off (ATL1 turns them on)
ATS0     spaces off, for compact replies
ATH0     headers off
ATSP0    automatic protocol search
0100     first request: which PIDs are supported?

Echo and linefeed settings are about tidiness. With echo on, the adapter repeats each command before replying, which helps when typing but clutters an app's parser. ATL1 adds a line feed after each carriage return, which some terminals need to show replies on separate lines.

• ATH1 shows the header bytes, including which module answered. On CAN cars, 7E8 is usually the engine computer.
• ATDP prints the protocol in words, and ATDPN prints its number.
• ATRV reads the voltage at pin 16, a quick battery check.
• ATI prints the version, the first step in spotting a clone.
• ATD restores the defaults when you have changed too much and lost track.

If a command returns a question mark, the chip does not know it. Clone firmware often lacks newer commands even when its version string claims otherwise, which is the whole story behind the v1.5 vs v2.1 debate.

Once auto search succeeds, ATDPN shows the number with an A in front, meaning it was found automatically. Write that number down; next time, ATSP followed by it skips the search.

Protocols 3 to 5 begin with a slow wake-up handshake, so the first request on those cars can take a few seconds. Later requests run faster once the link is open.

• Most US cars from 2008 on answer on 6.
• ATSPA6 tries 6 first but still falls back to searching if 6 fails.
• A car that answers on no protocol usually has the ignition off, a loose adapter or a blown fuse for the port.

The connection guide covers the fuse and fit checks in more detail.

>010C
41 0C 1A F8

Here A is 1A and B is F8 in hex, or 26 and 248 in decimal. So (256 × 26 + 248) ÷ 4 gives 1,726 RPM. A coolant reply of 41 05 7B works the same way: 7B is 123, and 123 minus 40 is 83 °C.

Other modes cover the rest of the OBD2 menu:

• 03 lists stored trouble codes, and 07 lists pending ones.
• 04 clears codes and freeze frame, and resets readiness monitors.
• 02 reads freeze frame data.
• 0902 requests the VIN on cars that support it.

The remaining pins, 1, 3, 8, 9, 11, 12 and 13, are left to each car maker. Ford uses 3 and 11 for its MS-CAN network, which is why FORScan cables carry a switch, and GM uses pin 1 for single-wire CAN. Pin 16 carries battery voltage even with the key out on most cars, which is why an adapter left plugged in stays powered and why sleep modes matter.

• Adapter has no power at all? Check pin 16; on many cars its fuse is shared with the power outlet.
• Powers up but finds no protocol? Check that the pins for your car's protocol are present in the port.
• Works on CAN cars only? The adapter may lack K-line or J1850 hardware.

For the Ford side of this, see the FORScan guide. For the software that sends these commands for you, the app guide lists the options by platform.