Modern vehicles are increasingly complex, packed with electronics and intricate systems. Accessing the wealth of information these systems hold has become essential for maintenance and repair. This is where the OBD2 port comes into play. Adopted by all vehicle manufacturers, the OBD2 port is now a standard feature in every car, providing a crucial interface for diagnostics.
The On-Board Diagnostics (OBD) standard was initially established by the California Air Resources Board (CARB). Its primary purpose was to monitor vehicle emissions and ensure compliance with pollution regulations. The advent of electronic engine control units (ECUs) and related sensors enabled vehicles to significantly reduce their emissions. OBD, in its core principle, mandates that a vehicle must continuously monitor the engine’s performance throughout its lifespan to ensure it operates cleanly.
Over time, OBD standards have evolved:
- OBD (OBDI): This initial standard focused on standardizing the diagnostic connector, making it uniform across vehicles. However, the communication protocols remained largely manufacturer-specific.
- OBDII: Introduced in the United States in 1996, OBDII aimed to establish common communication protocols, ensuring greater interoperability between diagnostic tools and vehicles.
- EOBD (European OBD): EOBD is the European adaptation of OBDII, specifically tailored for vehicles sold in Europe, and mirroring the OBDII specifications.
EOBD was implemented in Europe alongside the EURO3 emissions standard. It mandates that emission-related faults must be indicated by a warning light on the dashboard. Furthermore, the system requires vehicles to store Diagnostic Trouble Codes (DTCs) corresponding to any detected faults.
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OBD Standards and Implementation Dates
Following the EURO3 standard and European Directive 98/69/EC, the OBD standard became mandatory for vehicles based on the following dates:
While the directive mandated implementation for certain vehicle categories, some vehicles not directly impacted might still be compatible. This compatibility depended on manufacturers’ advancements beyond the directive requirements and their decision to activate the standard.
Note: Commercial vehicles and company cars are also subject to this directive, although their implementation dates may differ (e.g., 2006/2007).
The Malfunction Indicator Lamp (MIL) – Check Engine Light
Euro 3 and its associated directive brought about the introduction of a new warning light on vehicle dashboards: the Malfunction Indicator Lamp (MIL), commonly known as the “check engine light”. This indicator, represented by an engine symbol in orange/amber (red is prohibited for this purpose), as specified by ISO 2575, signals issues within the vehicle’s emission control system. Examples of this light are shown across various vehicle models below.
This light illuminates to indicate problems within the vehicle’s emission control system. Depending on the nature of the fault, different operating modes are possible:
- Solid Illumination: A fault affecting emission levels has been detected and confirmed by the ECU. The vehicle can typically continue to be driven.
- Flashing: A fault that could potentially damage vehicle components has been detected. In this scenario, it is strongly advised to stop the vehicle as soon as safely possible. This mode often accompanies a limp-home mode, limiting engine speed and power.
- Intermittent: A fault was detected, but the system has not consistently confirmed its presence. The light may turn off on its own.
- Off: In this state, no active emission-related faults are present. However, this does not guarantee the absence of all faults. Some issues with minimal impact on vehicle operation, such as malfunctioning glow plugs (as discussed in our OBD2 fault repair example), might not trigger this light.
The OBD Diagnostic Connector
The directive mandates that the diagnostic connector must be located within the vehicle’s passenger compartment. It’s commonly found under the steering wheel, in the fuse box compartment, or beneath the ashtray near the handbrake. This OBD2 port is where you connect an OBD diagnostic scanner to access vehicle information.
If you are having trouble locating your diagnostic connector, refer to our page on OBD connector locations for assistance.
Front view of the vehicle’s OBD connector (Dacia Logan shown)
Connector Pinout:
Note: Unused pins can be utilized by the manufacturer for specific needs.
| Pin Number | Description |
|---|---|
| 1 | |
| 2 | J1850 BUS+ (SAE) |
| 3 | |
| 4 | Chassis Ground |
| 5 | Signal Ground |
| 6 | CAN High |
| 7 | K-Line (ISO) |
| 8 | |
| 9 | |
| 10 | J1850 BUS- (SAE) |
| 11 | |
| 12 | |
| 13 | |
| 14 | CAN Low |
| 15 | L-Line (ISO) |
| 16 | Battery Positive (+) |
Understanding the OBD2 Standard
Although the OBD2 port itself is standardized, several communication protocols can be used, depending on the vehicle manufacturer. These protocols are broadly categorized under ISO 9141-2, ISO 14230, SAE J1850, ISO 15765, and SAE J1979 standards. ELM327-based interfaces are typically responsible for decoding these various communication standards.
Our diagnostic software is designed to translate the data frames from ELM interfaces into interpretable data, adhering to the SAE J1979 standard.
Different OBD Diagnostic Protocols
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Protocols Based on K and L Lines
The protocols described below all utilize the same physical medium (electrical connection). However, differences in the data transmission methods render them incompatible with each other.
ISO9141-2
This protocol is primarily used by European vehicle manufacturers.
ISO14230 (KWP2000 or KW2000)
ISO14230 is the successor to ISO9141, inheriting its core characteristics. This protocol is also predominantly used by European manufacturers. Within ISO14230, there are further sub-protocols, mainly differing in their initialization methods: slow init (5 baud init) and fast init.
KW1281, KW71, and KW82
These protocols (specified by SAE J2818) were mainly employed by German manufacturers (Audi, BMW, Volkswagen, Porsche) before the mandatory implementation of EOBD.
Protocols Based on SAE J1850
PWM (SAE J1850)
This protocol is primarily used by Ford. However, this may not always apply to Ford vehicles sold in Europe, which often utilize ISO protocols.
VPW (SAE J1850)
This protocol is predominantly used by General Motors.
CAN-Based Protocols
CAN (ISO 15765)
The Controller Area Network (CAN) protocol is intended to become the universally adopted standard for all vehicles. It offers superior speed and flexibility compared to older protocols.
CAN (SAE J1939)
This protocol is mainly used in heavy-duty vehicles such as trucks, agricultural machinery, and construction equipment.
Diagnostic connectors on heavy vehicles often differ and resemble the one shown above.
OBD Diagnostic Modes
Regardless of the communication protocol used, the OBD standard defines 10 diagnostic modes. Not all of these modes are necessarily supported by the engine control module (ECM). Newer vehicles are more likely to support a greater number of modes. Our OBD2 Vehicle Compatibility List provides examples of vehicles tested by users.
Mode 1
This mode provides live data or current values from various sensors, including:
- Engine speed (RPM)
- Vehicle speed
- Engine temperatures (intake air, coolant)
- Oxygen sensor information and air/fuel mixture regulation
Each sensor parameter is identified by a Parameter Identifier (PID). For example, the standard specifies PID 12 for engine speed. The OBD standard (updated in 2007) includes 135 PIDs. Similar to modes, not all vehicles support every PID. The vehicle compatibility list details the PIDs supported in different modes for specific vehicles.
Mode 2
Mode 2 displays freeze frame data. When a fault is detected by the ECM, it records sensor data at the precise moment the fault occurred. This snapshot of data helps in diagnosing the conditions under which the fault arose.
Mode 3
Mode 3 retrieves stored Diagnostic Trouble Codes (DTCs). These codes are standardized across vehicle manufacturers and categorized into four groups:
- P0xxx: Standard powertrain-related faults (engine and transmission)
- C0xxx: Standard chassis-related faults
- B0xxx: Standard body-related faults
- U0xxx: Standard network communication-related faults
More detailed information and definitions of generic DTCs are available on our Standard OBD Fault Codes page.
Mode 4
Mode 4 is used to clear stored DTCs and turn off the Malfunction Indicator Lamp (MIL).
Note: It is generally not advisable to clear a DTC without diagnosing and repairing the underlying issue. The MIL will likely illuminate again during the next drive cycle if the problem persists.
Mode 5
Mode 5 provides results from oxygen sensor/lambda sensor self-tests. It primarily applies to gasoline (petrol) vehicles.
For newer ECUs using CAN, Mode 5 is no longer used; Mode 6 replaces its functionalities.
Mode 6
Mode 6 reports the results of self-tests performed on systems not continuously monitored. This includes components like the catalytic converter and evaporative emission control system.
Mode 7
Mode 7 retrieves pending DTCs, also known as unconfirmed fault codes. This mode is valuable after a repair to verify that a fault code does not reappear without requiring an extended test drive. The codes used are the same as in Mode 3.
Mode 8
Mode 8 initiates on-board system tests or component tests. It is less commonly used in Europe.
Mode 9
Mode 9 provides vehicle information, such as:
- Vehicle Identification Number (VIN)
- Calibration Identification Numbers
Mode 10 (or Mode A)
Mode 10 retrieves permanent DTCs. These codes, identical to those in Modes 3 and 7, cannot be cleared using Mode 4. They will only be erased after multiple drive cycles without the reappearance of the problem, ensuring that the fault is genuinely resolved.
