Getting Started with OBD-II

Pages
Contributors: Toni_K
Favorited Favorite 18

OBD-II Protocols

There are five different communication protocols available under the OBD-II spec. Like so many things, manufacturers tend to have their preferences and think their protocol is best, hence the variation. Here's a quick overview of each and a description of the pins used on the DLC for each.

SAE J1850 PWM

This signal is Pulse Width Modulation, which runs at 41.6 kbps. This protocol is generally used on Ford vehicles.

SAE J1850 PWM
FeatureDescription
BUS + Pin 2
BUS - Pin 10
12V Pin 16
GND Pins 4, 5
Bus State:Active when BUS + is pulled HIGH, BUS - is pulled LOW
Maximum Signal Voltage:5V
Minimum Signal Voltage:0V
Number of bytes:12
Bit Timing:'1' bit - 8uS, '0' bit - 16uS, Start of Frame - 48uS

SAE J1850 VPW

This protocol is Variable Pulse Width, which runs at 10.4 kbps. GM vehicles typically use this version.

SAE J1850 VPW
FeatureDescription
BUS +Pin 2
12V Pin 16
GND Pins 4, 5
Bus State:Bus idles low
Maximum Signal Voltage:+7V
Decision Signal Voltage:+3.5V
Minimum Signal Voltage:0V
Number of bytes:12
Bit Timing:'1' bit -HIGH 64uS, '0' bit -HIGH 128uS, Start of Frame - HIGH 200uS

ISO 9141-2

If you have a Chrysler, European, or Asian vehicle, this is your protocol. It runs at 10.4 kbps and is asynchronous serial communication.

ISO 9141-2
FeatureDescription
K Line (bidirectional)Pin 7
L Line (unidirectional, optional)Pin 15
12V Pin 16
GND Pins 4, 5
Bus State:K Line idles HIGH. Bus is active when driven LOW.
Maximum Signal Voltage:+12V
Minimum Signal Voltage:0V
Number of bytes:Message: 260, Data: 255
Bit Timing:UART: 10400bps, 8-N-1

ISO 14230 KWP2000

This is the Keyword Protocol 2000, another asynchronous serial communication method that also runs at up to 10.4 kbps. This also is used on Chrsyler, European, or Asian vehicles.

ISO 14230 KWP2000
FeatureDescription
K Line (bidirectional)Pin 7
L Line (unidirectional, optional)Pin 15
12V Pin 16
GND Pins 4, 5
Bus State:Active when driven LOW.
Maximum Signal Voltage:+12V
Minimum Signal Voltage:0V
Number of bytes:Data: 255
Bit Timing:UART: 10400bps, 8-N-1

ISO 15765 CAN

This protocol has been mandated in all vehicles sold in the US from 2008 and later. However, if you have a European car from 2003 or later, the vehicle may have CAN. It's a two-wire communication method and can run at up to 1Mbps.

ISO 15765 CAN
FeatureDescription
CAN HIGH (CAN H)Pin 6
CAN LOW (CAN L)Pin 14
12V Pin 16
GND Pins 4, 5
Bus State:Active when CANH pulled HIGH, CANL pulled LOW. Idle when signals are floating.
CANH Signal Voltage:+3.5V
CANL Signal Voltage:+1.5V
Maximum Signal Voltage:CANH = +4.5V, CANL = +2.25V
Minimum Signal Voltage:CANH = +2.75V, CANL = +0.5V
Number of bytes:L
Bit Timing: 250kbit/sec or 500kbit/sec