Background
Background
General
Factors that have improved safety, increased comfort, added functions and increased environmental friendliness, have made modern vehicles more and more complicated.
The more complicated the vehicle is, the more important is the diagnostics system in the vehicle with the diagnostics tool when it comes to ensuring fast, safe and economic test, service and repair.
To reduce emissions from the vehicle, the diagnostic systems shall also, according to legislation, detect emission-influencing problems as well as defects that may cause follow-up damage on emission-related components.
Legal requirements emissions
OBD I - On Board Diagnostic I
On Board Diagnostic I (diagnostic system in the vehicle) was 1988 a requirement from CARB (California Air Resource Board) which is an air quality board. The purpose of these regulations was to ensure that component or function defects that affected exhaust emissions are detected by the control module's diagnostic functions.
OBD I included diagnosis of control module, emission-related components connected to the control module as well as exhaust gas recirculation.
Using the diagnostic socket in the engine compartment, the information about the system was accessible to all, both brand-name workshops and independent workshops.
In case of a detected emission-related problem, a warning light is activated in the driver information module (MIL= Malfunction Indicator Light), when the problem is confirmed as a real malfunction. Thus, the light is not activated immediately upon detection, only first when the malfunction is confirmed, which may be, e.g., following a few driving cycles.
OBD II - On Board Diagnostic II
On Board Diagnostic II was another requirement from CARB that applied from 1996. CARB demanded additional and refined diagnosis for emission-related component and systems in the drivetrain (engine and transmission).
Also, a standardized communication method was required for reading out of diagnosis (Standard SAE J1979 and J2190, where J2190 is voluntary and includes Enhanced Diagnostics - the vehicle manufacturer's own diagnosis in addition to legal requirements).
It should be possible to read out diagnostic trouble codes and their format, information connected to diagnostic trouble codes as well as parameters*, according to this standard. OBD II's diagnostic trouble codes are five-digit and begin with the letter P followed by four digits.
This standardized communication method means that anyone shall be able to manufacture and sell an instrument for reading out, a so-called Generic Scan Tool. Thus, the vehicle owner is not dependent on using a brand-name workshop.
The standard OBD II requires a standardized diagnostic socket in the passenger compartment near the driver's seat, where this instrument is to be plugged in. This means that the diagnostic socket (connector) is the same on all vehicles regardless of manufacturer or model.
However, there is a difference between manufacturers regarding which pins are used in the connector. This depends on the OBD II standard supports four types of communication protocols.
A protocol may be said to be the "language" that is to be used for communication with the control module.
Standardized pins on OBD II-connector:
- Pin 2 SAE J-1850 bus +
- Pin 4 Chassis ground
- Pin 5 Signal ground
- Pin 6 SAE J-2284, CAN-bus (CAN-H)
- Pin 7 SAE J1979, ISO 9141-2 / ISO14230-4, K-line
- Pin 10 SAE J-1850 bus -
- Pin 14 SAE J.2284, CAN-bus (CAN-L)
- Pin 15 ISO 9141-2 / ISO14230-4, L-line
- Pin 16 Voltage feed
Other pins in the connector are permitted for the vehicle manufacturer's own specific use. On pin 7 (K-line), two-way communication is permitted, on pin 15 (L-line) only one-way communication is permitted to the control module. Therefore, the L-line is missing in many vehicles.
ISO14230-4 = Protocol KWP2000.
OBD II was first introduced for Volvo on engine management system Motronic 4.3, Motronic 4.4, and automatic transmission AW 50 42, AW 30 40/43 in model 850/960 for market USA/CDN.
With time, OBD II-communication with control modules via CAN is introduced.
The legal requirement also includes the function Readiness Monitoring.
* Parameter refers to, e.g., rpm, engine temperature, battery voltage, etc., with associated value 800 rpm, 87 °C as well as 14,2 V, etc.
EOBD - European On Board Diagnostic
EOBD, European On Board Diagnostic is a legal requirement in Europe which, in principle, includes the same requirements as OBD II. EOBD applies to spark plug engines (gasoline engines) registered year 2000 and later, and self-igniting engines (diesel engines) registered 2003 and later.
For information about, among other diagnostic socket, see OBD II above.