All cars and light trucks built for sale in the United States after 1996 are required to be OBD-II compliant. There are five OBD-II protocol types in use: J1850 PWM, J1850 VPW, ISO 9141-2, ISO 14230 KWP2000, and ISO 15765 CAN.
SAE J1850 PWM (Pulse Width Modulation at 41.6 Kbps, two wire differential) Pin 2: BUS+ signal
Pin 10: BUS- signal
Active bus state: BUS+ is pulled high while BUS- is pulled low
High signal voltage level: +5V (min/max 3.80 to 5.25)
Low signal voltage level: 0V (min/max 0.00 to 1.20)
Up to 12 message bytes, excluding frame delimiters
Bit Timing;
"1" Bit: Bus state active for 8uS (within 24uS bit period)
"0" Bit: Bus state active for 16uS (within 24uS bit period)
Start-Of-Frame: Bus state active for 48uS |
SAE J1850 VPW (Variable Pulse Width at 10.4/41.6 Kpbs, single wire) Pin 2: BUS+ signal
Idle bus level is low
High signal voltage level: +7V (min/max 6.25 to 8.00)
Low signal voltage level: 0V (min/max 0.00 to 1.50)
Up to 12 message bytes, excluding frame delimiters
Bit Timing;"1" Bit: Signal low for 128uS or high for 64uS
"0" Bit: Signal low for 64uS or high for 128uS
Start-Of-Frame: Signal high for 200uS |
ISO 9141-2 (Asynchronous serial communication at 10.4 Kbaud) Pin 7: K-line bidirectional for communication
Pin 15: L-line (optional) unidirectional for waking up the ECU
Idle signal levels are high
Signals are active pull-down to 0V (0.00 to 2.40)
High signal voltage level: +12V (min/max 9.60 to 13.5)
Up to 12 message bytes, excluding frame delimiters
Bit Timing;
UART signaling at 10.4K baud, 8 data bits, no parity, 1 stop |
ISO 14230 KWP2000 (Asynchronous serial communication up to 10.4 Kbaud) Pin 7: K-line bidirectional for communication
Pin 15: L-line (optional) unidirectional for waking up the ECU
Idle signal levels are high
Signals are active pull-down to 0V (0.00 to 2.40)
High signal voltage level: +12V (min/max 9.60 to 13.5)
Message may contain up to 255 bytes in the data field
Bit Timing;
UART signaling up to 10.4K baud, 8 data bits, no parity, 1 stop |
ISO 15765 CAN (250kbit/sec or 500kbit/sec) Pin 6: CAN high (CANH)
Pin 14: CAN low (CANL)
Dominant or active bus state: CANH driven high while CANL driven low
Recessive or idle bus state: CANH and CANL signals are not driven
CANH signal voltage level: 3.5V (min/max 2.75 to 4.50)
CANL signal voltage level: 1.5V (min/max 0.5 to 2.25) |
At present, J1850 basically has no models to use, most of them use the latter three protocols, which are commonly known as K-line and CAN line.
