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9 pin D-SUB female connector layout
9 pin D-SUB female connector

ISO 9141-2. This protocol has an asynchronous serial data rate of 10.4 kbit/s. It is somewhat similar to RS-232; however, the signal levels are different, and communications happens on a single, bidirectional line without additional handshake signals. ISO 9141-2 is primarily used in Chrysler, European, and Asian vehicles.

  • pin 7: K-line
  • pin 15: L-line (optional)
  • UART signaling
  • K-line idles high, with a 510 ohm resistor to Vbatt
  • The active/dominant state is driven low with an open-collector driver.
  • Message length is Max 260Bytes. Data field MAX 255.

Simple OBD-2 iso9141-2 RS-232 cable schema

Components:
 

R1,2,6,7,9,10 - 560 ohm, 0.25W
R3,4,5,8 - 4K7 OHM, 0.125w
T1     - BC556 or 2N3906
T2,T3  - BC546 or 2N3904

One of our users reports that from collector of t1, r4 has to go to GND.

 

See also PC RS232 interface details.

Tx is -12V when inactive. therefore the diagram correctly shows that r4 goes to tx because it uses the -12V to pull down Rx when RS232 is in Rx mode.

16 pin J1962 OBD-2 car diagnostic connector layout
16 pin J1962 OBD-2 car diagnostic connector
According to 10 reports in our database (8 positive and 2 negative) this pinout should be correct.

Is this pinout
Source(s) of this and additional information: hem.passagen.se/tomasf/obd2/
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