Editing On-board diagnostics (section)

===OBD-II===
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 (automotive)|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 powertrain (engine and transmission), B for body, C for chassis, and U for network.

====OBD-II diagnostic connector====
[[Image:OBD 002.jpg|thumb|right|270px|Female OBD-II connector on a car]]
[[Image:OBD-II type A female connector pinout.svg|thumb|right|Female OBD-II type A connector pinout – front view]]
[[Image:OBD-II type B female connector pinout.svg|thumb|right|Female OBD-II type B connector pinout – front view. Wire placement is identical to type A, but the center groove is split in two.]]

The OBD-II specification provides for a standardized hardware interface — the female 16-pin (2x8) [[Data link connector (automotive)#OBD-II diagnostic connector|J1962 connector]], where type A is used for 12-volt vehicles and type B for 24-volt vehicles. Unlike the OBD-I connector, which was sometimes found under the bonnet of the vehicle, the OBD-II connector is required to be within {{convert|2|ft|m}} of the steering wheel (unless an exemption is applied for by the manufacturer, in which case it is still somewhere within reach of the driver).

SAE J1962 defines the pinout of the connector as:

{| class="wikitable"
|- valign="top"
!  1
| '''Manufacturer discretion'''<br>
GM: J2411 GMLAN/SWC/Single-Wire CAN.<br>
Audi: Switched +12 to tell a scan tool whether the ignition is on.<br>
VW: Switched +12 to tell a scan tool whether the ignition is on.<br>
Mercedes<ref>{{cite web |url=https://pinoutguide.com/CarElectronics/mercedes_obd2_diag_pinout.shtml |title=Mercedes PinOut |website=Pinoutguide.com |date=2019-09-30 |access-date=2022-12-27}}</ref> (K-Line): Ignition control (EZS), air-conditioner (KLA), PTS, safety systems (Airbag, SRS, AB) and some other.
!  9
| '''Manufacturer discretion'''<br>
GM: 8192 baud ALDL where fitted.<br>
BMW: RPM signal.<br>
Toyota: RPM signal.<br>
Mercedes (K-Line): ABS, ASR, ESP, ETS, BAS diagnostic.
|- valign="top"
! style="background-color: blue" |  2
| '''[[Bus (computing)|Bus]] positive Line'''<br>
[[SAE J1850]] PWM and VPW
! style="background-color: blue" | 10
| '''Bus negative Line'''<br>
SAE J1850 PWM only (not SAE 1850 VPW)
|- valign="top"
! 3
| '''Manufacturer discretion'''<br>
Ethernet TX+ (Diagnostics over IP)<br>
Ford DCL(+) Argentina, Brazil (pre OBD-II) 1997–2000, USA, Europe, etc.<br>
Chrysler CCD Bus(+)<br>
Mercedes (TNA): TD engine rotation speed.
! 11
| '''Manufacturer discretion'''<br>
Ethernet TX- (Diagnostics over IP)<br>
Ford DCL(-) Argentina, Brazil (pre OBD-II) 1997–2000, USA, Europe, etc.<br>
Chrysler CCD Bus(-)<br>
Mercedes (K-Line):&nbsp;Gearbox and other transmission components (EGS, ETC, FTC).
|- valign="top"
! style="background-color: gray" |  4
| '''Chassis ground'''
! 12
| '''Manufacturer discretion'''<br>
Ethernet RX+ (Diagnostics over IP)<br>
Mercedes (K-Line):&nbsp;All activity module (AAM), Radio (RD), ICS (and more)
|- valign="top"
! style="background-color: gray" |  5
| '''Signal ground'''
! 13
| '''Manufacturer discretion'''<br>
Ethernet RX- (Diagnostics over IP)<br>
Ford: FEPS – Programming PCM voltage<br>
Mercedes (K-Line):&nbsp;AB diagnostic – safety systems.
|- valign="top"
! style="background-color: lime" |  6
| '''CAN high'''<br>
(ISO 15765-4 and SAE J2284)
! style="background-color: lime" | 14
| '''CAN low'''<br>
(ISO 15765-4 and SAE J2284)
|- valign="top"
! style="background-color: yellow" |  7
| '''K-line'''<br>
(ISO 9141-2 and ISO 14230-4)
! style="background-color: yellow" | 15
| '''L-line'''<br>
(ISO 9141-2 and ISO 14230-4)
|- valign="top"
!  8
| '''Manufacturer discretion'''<br>
Activate Ethernet (Diagnostics over IP)<br>
Many BMWs: A second K-line for non OBD-II (Body/Chassis/Infotainment) systems.<br>
Mercedes: Ignition<br>
! style="background-color: red" | 16
| '''Battery voltage'''<br>
(+12 Volt for type A connector)<br>
(+24 Volt for type B connector)
|}

The assignment of unspecified pins is left to the vehicle manufacturer's discretion.<ref>{{cite web |url=https://pinoutguide.com/CarElectronics/car_obd2_pinout.shtml |title=OBD II diagnostic interface pinout |website=Pinoutguide.com |date=2017-12-02 |access-date=2022-06-28}}</ref>