obd2

The table below shows the standard OBD-II PIDs as defined by SAE J1979. The expected response for each PID is given, along with information on how to translate the response into meaningful data. Again, not all vehicles will support all PIDs and there can be manufacturer-defined custom PIDs that are not defined in the OBD-II standard.

Note that modes 1 and 2 are basically identical, except that Mode 1 provides current information, whereas Mode 2 provides a snapshot of the same data taken at the point when the last diagnostic trouble code was set. The exceptions are PID 01, which is only available in Mode 1, and PID 02, which is only available in Mode 2. If Mode 2 PID 02 returns zero, then there is no snapshot and all other Mode 2 data is meaningless.

Please, note that when using Bit-Encoded-Notation, quantities like C4 means bit 4 from data byte C. Each bit is numerated from 0 to 7, so 7 is the most significant bit and 0 is the least significant bit.

There are ten OBD-II PIDs modes of operation described in the latest OBD-II standard SAE J1979. They are as follows (the $ prefix indicates a hexadecimal radix):
$01. Show current data
$02. Show freeze frame data
$03. Show stored Diagnostic Trouble Codes
$04. Clear Diagnostic Trouble Codes and stored values
$05. Test results, oxygen sensor monitoring (non CAN only)
$06. Test results, other component/system monitoring (Test results, oxygen sensor monitoring for CAN only)
$07. Show pending Diagnostic Trouble Codes (detected during current or last driving cycle)
$08. Control operation of on-board component/system
$09. Request vehicle information
$0A. Permanent DTC’s (Cleared DTC’s)

Vehicle manufacturers are not required to support all modes.

Each manufacturer may define additional modes above #9 (e.g.: mode 22 as defined by SAE J2190 for Ford/GM, mode 21 for Toyota) for other information (e.g.: the voltage of the Traction Batter

OBD-II PIDs (On-board diagnostics Parameter IDs) are codes used to request data from a vehicle, used as a diagnostic tool. SAE standard J/1979 defines many PIDs, but manufacturers also define many more PIDs specific to their vehicles. All light duty vehicles (i.e. less than 8,500 pounds) sold in North America since 1996, as well as medium duty vehicles (i.e. 8,500-14,000 pounds) beginning in 2005, and heavy duty vehicles (i.e. greater than 14,000 pounds) beginning in 2010, are required to support OBD-II diagnostics, using a standardized data link connector, and a subset of the SAE J/1979 defined PIDs (or SAE J/1939 as applicable for medium/heavy duty vehicles), primarily for state mandated emissions inspections.

Typically, an automotive technician will use PIDs with a scan tool connected to the vehicle’s OBD-II connector.

• The technician enters the PID
• The scan tool sends it to the vehicle’s bus (CAN, VPW, PWM, ISO, KWP. After 2008, CAN only)
• A device on the bus recognizes the PID as one it is responsible for, and reports the value for that PID to the bus
• The scan tool reads the response, and displays it to the technician

There are five signaling protocols that are permitted with the OBD-II interface. Most vehicles implement only one of the protocols. It is often possible to deduce the protocol used based on which pins are present on the J1962 connector:

• SAE J1850 PWM (pulse-width modulation — 41.6 kB/sec, standard of the Ford Motor Company)
  • pin 2: Bus+
  • pin 10: Bus–
  • High voltage is +5 V
  • Message length is restricted to 12 bytes, including CRC
  • Employs a multi-master arbitration scheme called ‘Carrier Sense Multiple Access with Non-Destructive Arbitration’ (CSMA/NDA)
• SAE J1850 VPW (variable pulse width — 10.4/41.6 kB/sec, standard of General Motors)
  • pin 2: Bus+
  • Bus idles low
  • High voltage is +7 V
  • Decision point is +3.5 V
  • Message length is restricted to 12 bytes, including CRC
  • Employs CSMA/NDA
• ISO 9141-2. This protocol has an asynchronous serial data rate of 10.4 kBaud. 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 V_batt
  • The active/dominant state is driven low with an open-collector driver.
  • Message length is restricted to 12 bytes, including CRC
• ISO 14230 KWP2000 (Keyword Protocol 2000)
  • pin 7: K-line
  • pin 15: L-line (optional)
  • Physical layer identical to ISO 9141-2
  • Data rate 1.2 to 10.4 kBaud
  • Message may contain up to 255 bytes in the data field
• ISO 15765 CAN(250 kBit/s or 500 kBit/s). The CAN protocol was developed by Bosch for automotive and industrial control. Unlike other OBD protocols, variants are widely use outside of the automotive industry. While it did not meet the OBD-II requirements for U.S. vehicles prior to 2003, as of 2008 all vehicles sold in the US are required to implement CAN as one of their signaling protocols.
  • pin 6: CAN High
  • pin 14: CAN Low

All OBD-II pinouts use the same connector, but different pins are used with the exception of pin 4 (battery ground) and pin 16 (battery positive).

OBD-II is an improvement over OBD-I in both capability and standardization. The OBD-II standard specifies the type of diagnostic connector and its pinout, the electrical signalling protocols available, and the messaging format. It also provides a candidate list of vehicle parameters to monitor along with how to encode the data for each. There is a pin in the connector that provides power for the scan tool from the vehicle battery, which eliminates the need to connect a scan tool to a power source separately. However, some technicians might still connect the scan tool to an auxiliary power source to protect data in the unusual event that a vehicle experiences a loss of electrical power due to a malfunction.

 

Finally, the OBD-II standard provides an extensible list of DTCs. As a result of this standardization, a single device can query the on-board computer(s) in any vehicle. This OBD-II came in two models OBD-IIA and OBD-IIB. OBD-II standardization was prompted by emissions requirements, and though only emission-related codes and data are required to be transmitted through it, most manufacturers have made the OBD-II Data Link Connector the only one in the vehicle through which all systems are diagnosed and programmed. OBD-II Diagnostic Trouble Codes are 4-digit, preceded by a letter: P for engine and transmission (powertrain), B for body, C for chassis, and U for network.