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Ultimate OBD2 Guide: Understanding Vehicle Diagnostics

Updated at 16 Feb, 2023

— From novice to expert, our OBD2 guide dives deep into car diagnostic systems. Empower yourself with the know-how to troubleshoot vehicle issues.

Ultimate OBD2 Guide: Understanding Vehicle Diagnostics
Welcome to our simple guide on the OBD2 system. OBD2 became mandatory in all newer cars from 1996, and in the United States in 2021 - 282 million vehicles were registered. So you can imagine how many of today's vehicles are depending on this system for diagnostics. Dive in with us as we uncover its many attributes.

If you're a developer, whether novice or expert, or manage a fleet of vehicles, you understand the importance of consistent maintenance to ensure smooth operations. But, are you familiar with OBD2 and its functionality?

The OBD2 system tracks your vehicle's health and pinpoints problems that might be the cause.

This guide will walk you through everything you need to know about OBD2, highlighting its main features, information, and its key elements.


What is OBD2?

In short, OBD2, or OBD-II, is a diagnostics system found in today's cars and trucks.

It's like the vehicle's health check mechanism, consistently monitoring different parts and systems. When it system detects a potential problem, a light will pop up on your dashboard as an alert.

The OBD2 system gathers crucial information from various sensors throughout the vehicle. The car's engine control unit (ECU), acting as the vehicle's brain, processes this information to pinpoint issues. This could range from problems with the engine, exhaust emissions, or even fuel efficiency.

For example, if you've ever noticed your fuel consumption becoming less efficient, the OBD2 might identify a faulty oxygen sensor as the culprit, signaling you to address the issue before it worsens.

This is the car's way of telling you, that there is a problem within its system, by showing you the malfunction indicator light on your dashboard.

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How Does OBD2 Work?

OBD2 gathers information from sensors located in your car's engine and other systems.

When it detects an issue, it produces diagnostics trouble codes (DTC). These codes can be read using a OBD2 scanner or vehicle telematics device, helping you understand and fix any vehicle performance hitches.

You connect the telematics device to the OBD2 port, typically found under the car's dashboard, but can be found in other areas as well (seen in the image below).

This port has a standard design that lets the diagnostics device communicate with the car's main computer (CAN bus) and fetch the DTCs.

How Does OBD2 logs data?

The OBD2 system continuously monitors various parameters within the vehicle. As it collects data, it compares this information to pre-set standards.

If any discrepancies or anomalies are detected, the system flags these as potential issues, translating them into DTCs. These codes are then stored within the onboard computer, ready to be accessed by diagnostic tools.

How to Use an OBD2 Scanner?

Using an OBD2 scanner is a straightforward process that involves a few simple steps, i.e., you have an OBD2 scanner.

Here's a basic overview of how to use an OBD2 scanner.

  1. Locate the OBD2 port: The OBD2 port is often found under the dashboard on the driver's side of the vehicle. The most common places are seen in the image below.

  2. Turn on the ignition: Turn the key to the "On" position, but do not start the engine. This will enable the OBD2 system to connect with the scanner.

  3. Connect the scanner: Connect the OBD2 scanner to the port. Depending on the make and model of the vehicle, you might need additional cables or adapters.

  4. Read the Diagnostic Trouble Codes (DTCs): Once the scanner is connected, follow the instructions by the manufacturer to read the DTCs from the car's onboard computer. The scanner may also display other relevant information, such as sensor reading and real-time data.

  5. Interpret the results: After reviewing the DTCs, use the scanner's manual or internet resources to interpret the data. With each code, the scanner should offer a summary of the problem. Remember, that some codes may need additional testing or examination to determine the main cause of the problem.

  6. Clear the codes: After identifying the issue, use the scanner to clear the DTCs. This will reset the system and turn off the dashboard's check engine light. Remember, that just clearing the codes without addressing the underlying problem may result in the check engine light returning. This is how you reset DTC codes.

Overall, using an OBD2 scanner may assist car owners and mechanics in diagnosing and addressing any performance issues with a vehicle. You might save money on repairs and ensure your vehicle is functioning at peak performance by routinely checking the diagnostics using an OBD2 scanner.

An OBD scanner device surrounded by icons representing different types of vehicle analytics.

OBD2 and CAN bus Connection

The OBD2 diagnostics act as a higher layer protocol, while the CAN serves as its communication method. The OBD2 standard defines a distinct connector, encompassing five main protocols.

Notably, since 1996, the CAN bus has been an essential OBD2 protocol for all vehicles in the U.S. By 2001, Europe mandated all cars to be OBD2 compliant, and this became a requirement in Australia and New Zealand starting 2006.


When it comes to determining if your vehicle is equipped with an OBD2 (On-Board Diagnostics II) system, the key factors to consider are not where your car was manufactured or initially purchased. Instead, compatibility hinges on the model year and specific regulations applicable to the country where the vehicle was sold new. Below, we simplify the process of figuring out your car's OBD2 status, so you can easily understand what to look for.

If your car is newer than 1996 in the US, or 2001 in the EU, then your car is most likely OBD2 compatible.

Please note: This list serves as a simplified guide. Vehicle compatibility with OBD2 can be influenced by specific models or manufacturer practices. Always consult your vehicle's manual or contact the dealership for the most accurate information.

Country of Sale
Model Years Covered
Important Notes
USA 1996 and newer All petrol-powered vehicles are OBD2 compliant from 1996 onwards. Diesel vehicles followed suit in 2004.
European Union 2001 and newer (petrol) / 2004 and newer (diesel) Includes member states as of the implementation dates. Check specific regulations for vehicles sold under "Euro 6" standards.
Japan 2002 and newer JDM vehicles typically comply from 2002, but imported vehicles might differ; verify with the manufacturer.
Australia 2006 and newer Australian Design Rules (ADR) incorporate OBD2 compliance from 2006 for most passenger vehicles.
Canada 1998 and newer Canadian vehicles align closely with US standards, adopting OBD2 in 1998 for gasoline vehicles.

The five OBD2 signal protocols

Diving into the world of car diagnostics, think of the OBD2 system as the main artery of communication in your vehicle. But here’s the twist: not all cars speak the same language. Picture five dialects under the OBD2 umbrella, each with its own flair and rules. It's like choosing the right fuel for your ride; picking the correct OBD2 protocol is key for smooth chats between your car and the diagnostic gear, shining a light on the car's health.

Why so many, you ask? It’s a mix of history’s favorites and the needs of now, blending old-school cool with modern tech. Coming up, we’ve got a neat snapshot of these five communication styles. Our table’s packed with the need-to-knows — from pin setups to voltage vibes — making it easier for you to get the gist of your car's internal conversations and how it gets along with diagnostic tools.

SAE J1850 PWM

Primarily used in Ford vehicles, this protocol communicates at 41.6 kbps, using Pulse Width Modulation to ensure reliable data transmission between the vehicle's systems and diagnostic tools.

Feature
Description
SAE J1850 PWM (Ford) Bus +: Pin 2, Bus -: Pin 10, 12V: Pin 16, GND: Pins 4, 5, State: Active when BUS + HIGH, BUS - LOW, Voltage: Max 5V, Min 0V, Bytes: 12, Bit Timing: '1' bit - 8uS, '0' bit - 16uS, Start of Frame - 48uS

SAE J1850 VPW

Favoured by General Motors, it operates at speeds of 10.4/31.6 kbps with a Variable Pulse Width, offering a unique method for data exchange that enhances diagnostic efficiency.

Feature
Description
SAE J1850 VPW (GM) Bus +: Pin 2, 12V: Pin 16, GND: Pins 4, 5, State: Idles low, Voltage: Max +7V, Decision +3.5V, Min 0V, Bytes: 12, Bit Timing: '1' bit - HIGH 64uS, '0' bit - HIGH 128uS, Start of Frame - HIGH 200uS

ISO 9141-2

A choice for Chrysler, European, and Asian vehicles, this protocol facilitates asynchronous serial communication at 10.4 kbps, similar to RS-232, but with automotive-specific signal levels for broad compatibility.

Feature
Description
ISO 9141-2 (Chrysler, Euro, Asian) K Line: Pin 7, L Line (optional): Pin 15, 12V: Pin 16, GND: Pins 4, 5, State: K Line idles HIGH, active when LOW, Voltage: Max +12V, Min 0V, Bytes: Message 260, Data 255, Bit Timing: UART 10400bps, 8-N-1

ISO 14230 KWP2000

Also known as the Keyword Protocol 2000, it extends the capabilities of ISO 9141-2 by offering speeds up to 10.4 kbps and supports a wide range of vehicle diagnostic operations, especially in Chrysler, European, and Asian models.

Feature
Description
ISO 14230 KWP2000 (Chrysler, Euro, Asian) K Line: Pin 7, L Line (optional): Pin 15, 12V: Pin 16, GND: Pins 4, 5, State: Active when LOW, Voltage: Max +12V, Min 0V, Bytes: Data 255, Bit Timing: UART 10400bps, 8-N-1

ISO 15765 CAN

The backbone of modern vehicle diagnostics, this protocol is mandatory for all vehicles sold in the US from 2008 onwards. Operating at 250 kbit/s or 500 kbit/s, it leverages the CAN bus system for high-speed, robust data communication across the vehicle's network.

Feature
Description
ISO 15765 CAN (US 2008+, Euro 2003+) CAN HIGH (H): Pin 6, CAN LOW (L): Pin 14, 12V: Pin 16, GND: Pins 4, 5, State: Active CANH HIGH, CANL LOW, Idle floating, Voltage: CANH Max +4.5V, Min +2.75V; CANL Max +2.25V, Min +0.5V, Bit Timing: 250kbit/sec or 500kbit/sec
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The OBD2 Connector and Pinout

The OBD2 connector allows for easy data retrieval from your vehicle. The AutoPi TMU male connector pinout (here's how it looks like) is designed to interface with the female OBD2 16-pin (2x8) J1962 connector, which is a universal hardware interface.

Unlike OBD1 connector, often found near the hood, the OBD2 connector is commonly positioned within 2 feet (0.61m) of the steering wheel. Below is a detailed image of the OBD2 female connector pinout.

Diagram of an OBD-II connector highlighting CAN bus and other protocol pins.

Quick overview of the OBD2 Port pinouts

The OBD2 port features a configuration of 16 pins, each tailored for a unique role within the system:

  • Pins 4 and 5 serve a fundamental purpose: they provide grounding to ensure safe and accurate data transmission.

  • For direct communication with the vehicle's main computer system, pins 2 and 10 come into play, specifically communicating with the SAE J1850 BUS+.

  • Central to many diagnostics processes, pins 6 and 14 are essential. They establish a connection to the CAN bus, a crucial communication channel outlined by the ISO 15765-4 standard.


Generally, you will find the OBD2 port under the dashboard panel and near the steering wheel.

If you're wondering, "Where exactly is my OBD2 port?", then we have made an image below that gives a clear representation.

Most often, it's located beneath the dashboard and the steering wheel, as indicated by numbers 1-3 in the illustration. However, certain car models might have the port in alternative locations, as highlighted by numbers 4-9 in the depiction.

Car dashboard diagram indicating the typical location of the OBD2 port.

In this Youtube video, we have showcased how to find the OBD2 port and how to connect your AutoPi TMU device to the OBD2 port (Skip to 0:24).

History and the difference between OBD1 and OBD2

The history of On-board Diagnostics goes back to the 1960s when several organizations started discussing the necessity of having the OBD to detect emission failures.

Specifically, the organizations that supported it were the California Air Resources Board (CARB), the International Organization for Standardization (ISO), the Environmental Protection Agency (EPA), and the Society of Automotive Engineers (SAE).

In 1982, CARB began developing regulations requiring all vehicles to have an OBD port.

Up until recently, the UN commissioned the ISO to develop the WWH-OBD standard, however, it is currently being defined. More on this subject will come out soon.

Timeline

1968: VW introduced the first OBD computer system with scanning capability.

1975: Datsun began using onboard computers in consumer vehicles.

1980: GM implemented an interface and protocol to test the Engine Control Module (ECM).

1988: CARB required all vehicles sold in California from 1988 and newer, to have a simple OBD capability as a minimum.

1994: CARB pushed the requirement further and issued the OBD2 specification in all vehicles sold in California from 1996.

1996: All cars sold in the US needed to be OBD2 compatible.

2001: EU made it mandatory for manufacturers to include OBD2 in all gasoline vehicles sold in the EU.

2004: EU made it mandatory for manufacturers to include OBD2 in all diesel vehicles sold in the EU.

2006: All vehicles manufactured in Australia and New Zealand were required to be OBD2 compatible.

2008: All vehicles sold in the US were required to use the signaling standard ISO 15765-4 (CAN).

Infographic detailing the historical milestones of OBD1 and OBD2 in the automotive industry.

OBD1 vs. OBD2

OBD, or OBD1, was used during the earlier years of the car manufacturing industry and was used to connect to the console of a car, while OBD2 (OBD-II) was introduced in car models produced in the early 1990s, and is remotely connected to the vehicle.

OBD2 is an advanced version of OBD1 and offers better signaling protocols and messaging formats. Furthermore, it provides better results for vehicle parameters when used in the emission control system.

Detailed information between OBD1 and OBD2

How AutoPi Can Contribute To Your OBD2 Project

Elevate your OBD2 project with the cutting-edge AutoPi device. This versatile device not only seamlessly communicates with your car's ECUs and the intricate CAN bus system but also effortlessly plugs into the OBD2 port, serving as the nerve center for your automotive diagnostics.

With AutoPi, dive into advanced OBD2 data logging capabilities. Connect our robust OBD2 logger to your vehicle's OBD2 connector and embark on a data journey. Send "request frames" to solicit information, and receive detailed "response frames" through the CAN network, unlocking a treasure trove of diagnostic insights.

But why stop there? Decode the complex language of raw OBD2 responses with tools like the OBD2 DBC, transforming cryptic data into actionable insights. The AutoPi device goes a step further, allowing the use of a CAN logger to dispatch custom CAN frames, doubling as a sophisticated OBD2 logger.

Remember, compatibility is key. Vehicles differ in the model/year-specific OBD2 PIDs they support. With AutoPi, you're equipped to navigate these variations, ensuring a smooth and efficient diagnostic process across a wide range of vehicles.

Choose AutoPi device for your OBD2 project, and harness the power of smart, seamless, and sophisticated vehicle diagnostics. Unleash the full potential of your automotive endeavors with AutoPi.

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