The OBD-II standard (On-Board Diagnostic) was implemented initially by the CARB (Californian Air Resources Board) to control the polluting emissions from vehicles. The arrival of electronic computers to manage the engine and associated computers enabled vehicles to reduce their pollutants. The OBD states that a vehicle should permanently monitor the smooth operation of the engine throughout its life

The OBD stands for On/Off-Board Diagnostic, Basically, this OBD-II term is used in the automotive vehicles for the diagnostic of the vehicle. Now you would have thought about diagnostic which means to find the cause or fault of a problem.  If you are a man and going to the hospital if you have any problem then you can think and explain it to the doctor and he will give you the solution. But if any problem is occurring in your vehicle, then how the vehicle will explain it to the service engineer when any fault is happening as he is a machine whose not having the thinking capability. If you are purchasing a vehicle and going to the service center where if you don’t know the proper fault, then they will check everything one by one and they might be again made some problem and more time, more cost, they will put some more parts which might cost you more for which you can’t say anything. So to prevent this nowadays most of the OEM started using the diagnostic system in the vehicle. Basically the Diagnostic is of having two types as:

  • On-Board Diagnostic.
  • Off-Board Diagnostic.

(1)  Off-Board Diagnostic: If the fault is happening and to detect the fault, the diagnostic engineer using some external tool to do the diagnostic on the vehicle and fix the problem, then this is called Off-Board diagnostic.

(2)  On-Board Diagnostic: If any fault will occur in the vehicle and the OEM is already has been implemented some codes to check the fault periodically in every ECU to detect the fault and immediately inform the owner about the fault, then this is called an On-Board Diagnostic.

Since the On-Board diagnostic or OBD-II is the concept to which all the OEM’s are following which really helping them to do the self-diagnostic in-vehicle system and also save the money mostly they are using the term OBD means On-Board diagnostic. So that now I am going to explain this On-Board diagnostic so from next time onward you have to understand OBD means On-Board Diagnostic.

The OBD-II is a term that is used for self-diagnostic and reporting capability. First, automotive OEM has started this concept to give safety to the engine A basic OBD system consists of an ECU (Electronic Control Unit), which uses input from various sensors (e.g., oxygen sensors) to control the actuators (e.g., fuel injectors) to get the desired performance. The “Check Engine” light, also known as the MIL (Malfunction Indicator Light), provides an early warning of malfunctions to the vehicle owner. A modern vehicle can support hundreds of parameters, which can be accessed via the DLC (Diagnostic Link Connector) using a device called a scan tool.

There are two types of OBD are available which are using in vehicles for fault diagnostic. Such as OBD-I & OBD-II.OBD-I: The OBD-I refers to the first generation OBD systems that were developed throughout the 1980s. These early systems use proprietary connectors, hardware interfaces, and protocols. A mechanic who wanted to access the diagnostic information typically had to buy a tool for every different vehicle make. OBD-I scan tools that support multiple protocols are supplied with an array of different adapter cables. This standard was very difficult to manage with different automotive makers for a mechanic. Then the OBD-II came to the automotive industry which solves all the problems

OBD-II: Unlike earlier, OEM-specific OBD-I systems, The OBD-II systems use the same communication protocols, code designations, and connectors from one manufacturer to another. This allows a single OBD-II scanner to provide access to the data that these systems are capable of providing across all makes and models of vehicles produced since 1996, which was the first model year that OBD-II was required across the board. In the early 1990s, the Society of Automotive Engineers (SAE) and International Standardization Organization (ISO) issued a set of standards that described the interchange of digital information between ECUs and a diagnostic scan tool. All OBD-II compliant vehicles were required to use a standard diagnostic connector (SAE J1962), and communicate via one of the standard OBD-II communication protocols.

OBD-II has first introduced in model year (MY) 1994 vehicles and became a requirement for all cars and light trucks starting with MY1996. Virtually every new car sold in the U.S. over the past 20 years follows the OBD-II standard. OBD-II cars have a port — usually located under the dashboard on the driver’s side — that devices can plug into and connect to a car’s computer. Companies have plenty of ideas about what you can plug into that port.

Types Of OBD-II Scanners: There are basically two types of OBD-II scanners that you will come across in the wild.

(1) OBD-II Code Reader.

(2) OBD-II Scan Tool.

(1) OBD-II Code Reader: The OBD-II code (DTC) reader is one of the simplest vehicle diagnostic tool used to read the fault codes from the vehicle. These devices are designed to interface with a car’s computer and report trouble codes in a very no-frills sort of way. Cars and trucks that were built prior to 1996 require specific, proprietary code readers, and newer vehicles use universal code readers. This type of car code reader is typically inexpensive, and some parts stores and shops will even read your codes for free. The OBD-II code readers are typically inexpensive.

code reader for obd ii
OBD-II Code Reader

Features of OBD-II Code Reader:

(a) Read and Clear of fault codes(DTC).

(b) Check of view of basic Parameter ID’s.

(c) Check and possibly reset readiness monitors.

(2) OBD-II Scan Tool: An OBD scan tool is a vehicle diagnostic scan tool which is the advanced version of the Code reader tool. The OBD scan tool exhibits a wide range of features. The scan tools typically include a code reader, which has the ability to view and sort live data, and some type of knowledge base. Whereas the professional scan tools include extensive knowledge bases, diagnostic procedures, and sometimes even have built-in scopes, multimeters, and other diagnostic tools.

What Can a Scan Tool Do?

The scan tools are designed to interface with a car’s “onboard diagnostic” system in order to facilitate the diagnostic process. In that way, they are a lot like car code readers. They can be plugged into an OBD-I or OBD-II socket, read and clear codes, and view data readouts from various sensors. However, scan tools go beyond that basic functionality.

scan tool obd ii
OBD Scan Tool

Featurs Of OBD Scan Tool:

  • It can Store and playback live data.
  • It can Display Graph data.
  • It can Read both generic and manufacturer-specific trouble codes.
  • It can Display pending codes.
  • It can Provide trouble code definitions.
  • It can Provide troubleshooting procedures or tips.

OBD-II Connector: The OBD-II connector is available in every vehicle nowadays through which the diagnostic engineer will connect the OBD/diagnostic tool with the vehicle to find the faults. Nowadays the OEM’s are also providing wireless communication like Bluetooth/Wi-fi through which users can connect the Diagnostic tool or the android software provided by the Manufacturer to scan the faults. 

But there is a standard that all the OEM are following and providing the OBD-II connector port in the vehicle. The SAE-J1962 specification provides for two standardized hardware interfaces, called type A and type B. Both are female, 16-pin (2×8), D-shaped connectors, and both have a groove between the two rows of pins, but type B’s groove is interrupted in the middle. This prevents the insertion of a type A male plug into a type B female socket while allowing a type B male plug to be inserted into a type A female socket.

(a) Type-A OBD connector: The type-A OBD connector is used for vehicles that use 12V supply voltage.

(b) Type-B OBD connector: The type-B is used for 24V vehicles and it is required to mark the front of the D-shaped area in blue color.

obd ii conector
OBD-II Conector

The SAE J1962  standard OBD-II Connector details


Manufacturer discretion:

1. GM: J2411 GMLAN/SWC/Single-Wire CAN
2. VW/Audi/BMW: Switched +12V to tell a 
scan tool whether the ignition is on.
3. Ford, FIAT: Infotainment CAN High
4. DoIP Option #2 Ethernet RX+
9  Manufacturer discretion:

1. BMW: TD (Tachometer Display) signal aka engine RPM signal.
2. GM: 8192 bit/s ALDL where fitted.
3. DoIP Option #2 Ethernet RX-
2Bus Positive Line of SAE J-1850 PWM and VPW10Bus Negative Line of SAE J1850 PWM only (not SAE J1850 VPW)
Manufacturer discretion:

1. GM: Object Detection CAN bus (+)
2. Ford: DCL(+) Argentina, Brazil (pre OBD-II) 1997–2000, USA, Europe, etc.
3. Ford: Medium Speed CAN-High
4. Chrysler: CCD Bus(+)
5. BMW: Ethernet RX+
6. DoIP Option #1 Ethernet RX+
Manufacturer discretion:

1. GM: Object Detection CAN bus (-)
2. Ford: DCL(-) Argentina, Brazil (pre OBD-II) 1997–2000, USA, Europe, etc.
3. Ford: Medium Speed CAN-Low
4. Chrysler: CCD Bus(-)
5. BMW: Ethernet RX-
6. DoIP Option #1 Ethernet RX-
Chassis ground
Manufacturer discretion:

1. GM: Chassis high-speed CAN bus (+)
2. GM: Diagnostic codes to DIC (1994–2004 Corvette)
3. BMW: Ethernet TX+
4. DoIP Ethernet TX+
Signal ground
Manufacturer discretion:

1. GM: Chassis high-speed CAN bus (-)
2. Ford: FEPS – Programming PCM voltage
3. BMW: Ethernet TX-
4. DoIP Ethernet TX-
CAN-High (ISO 15765-4 and SAE J2284)
CAN-Low (ISO 15765-4 and SAE J2284)
K-Line of ISO 9141-2 and ISO 14230-4
L-Line of ISO 9141-2 and ISO 14230-4
Manufacturer discretion:

1. BMW: Second K-Line for non OBD-II (Body/Chassis/Infotainment) systems.
2. Ford, FIAT: Infotainment CAN-Low.
3. BMW: Ethernet Enable via 510 Ohm, 0,6 Watt resistance to battery voltage (pin 16)
4. DoIP: Ethernet Activate
5. Subaru: Ignition+.
Battery voltage:

1. Type “A” 12V/4A
2. Type “B” 24V/2A

Unlike the OBD-I connector, which was sometimes found under the hood of the vehicle, the OBD-II connector is required to be within 2 feet (0.61 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).

OBD-II Output:

The data coming from OBD-II is of two forms: Diagnostics Trouble Codes and Real-time monitoring. Real-time data can be acquired and stored for further processing and analysis. 

How to understand the OBD-II Code:

When the scanner finishes booting up, look for a menu. Select “Codes” or “Trouble Codes” to open the main Codes menu. Depending on your scanner and year of the vehicle you may be presented with a few systems such as Engine/Powertrain, Transmission, Airbag, Brakes, etc. When you pick one, you will see two or more types of codes. The most common are Active codes and Pending codes.

  • Active codes are live codes or malfunctions that are keeping your Check Engine Light on. Just because your Check Engine Light is off doesn’t mean the code or malfunction disappeared, it just means that the code setting conditions haven’t occurred for two or more operations of the vehicle.
  • Pending codes mean that the OBD-II monitoring system has failed the operation of an emission control system at least once and if it fails again the Check Engine Light will be turned on and the malfunction becomes an Active code.
obd diagnostic trouble codes
OBD-II Diagnostic Trouble Codes

what system the code is referring to. There are several letters that you may see, though you may have to move to different menus to see them:

  • P – Powertrain. This covers the engine, transmission, fuel system, ignition, emissions, and more. This is the largest set of codes.
  • B – Body. This covers airbags, seat belts, power seating, and more.
  • C – Chassis. These codes cover ABS, brake fluid, axles, and more.
  • U – Undefined. These codes cover other aspects of the car.

How to detect the type of DTC from it’s character Name:?

P0xxx, P2xxx, and P3xxx are all generic codes that apply to all makes and models. P1xxx codes are manufacturer specific, such as Honda, Ford, Toyota, etc. The second number tells you what subsystem the code refers to. For example, P07xx codes refer to transmission.

Read an example code: In OBD-II standard, P0301 indicates a misfire condition on cylinder #1. The P indicates it’s a powertrain code, the 0 indicates that it is a generic or universal code. The 3 means the area or subsystem is an Ignition System code.

  • The 01 indicates it’s a cylinder specific problem, in that there is a misfire condition in the number 1 cylinder. It could mean that the spark plug, plug wire, or dedicated ignition coil are worn out or that there is a vacuum leak near the cylinder.
  • Code does not tell you what component is defective; it only points to or indicates that a component, its circuit, or its wiring/vacuum control are malfunctioning. The code may be the symptom of a malfunction caused by a completely different system.

How Diagnose your vehicle:

The proper diagnosis of OBD-II codes takes years of training and practice. For example, a weak battery or worn out alternator can set five or more codes in systems that are perfectly normal. Before attempting repairs, understand that the codes alone will not tell you what parts need to be replaced or what repairs need to be made.

  • If you are unsure of what you are doing, take your car to an ASE Certified Master Technician with the L1 Advanced Engine Performance Diagnostic certification, or you could end up wasting a lot of time and money.
obd ii scanner
OBD-II Scanner

What OBD-II can do?

It can read the faults from the vehicle for diagnostic and it also can monitor the vehicle.

obd ii fault read
OBD-II Fault Read
  • Gathering Enginee Parameters: The engine parameters like RPM, VSS, MAF, MAP, Coolant Temperature, Power, Torque, & engine load, etc. can be gathered.
  • Developing Drive Cycles: Gear information, engine RPM, throttle position, torque, speed, & power can be recorded which later can be used to develop the drive cycles for testing.
  • Determining Fuel Economy: The various parameters like MAF, MAP, IAT, & VSS data can be used to determine the fuel economy of the vehicle.
  • Understanding Drive Patterns: The OBD-II data can be used to monitor the drive patterns which can help in analyzing the driving habits of a person. The insurance companies are trying to link the insurance of a vehicle with the driving pattern of the person.
  • Traffic Conditio0ns: The traffic conditions can be categorized based on speed & RPM. The GPS location can be logged to find the traffic zones. This can be done by connecting a small OBD-II device to the car OBD port.

How to read DTC from Vehicle using different Diagnostic Service?

The OBD-II PIDs (On-board diagnostics parameter IDs) are codes used to request data from a vehicle, used as a diagnostic tool. SAE standard J1979 defines many OBD-II PIDs. All on-road vehicles and trucks sold in North America are required to support a subset of these codes, primarily for state-mandated emissions inspections. Manufacturers also define additional PIDs specific to their vehicles. Though not mandated, many motorcycles also support OBD-II PIDs.

OBD-II Modes Of Services:

There are 10 diagnostic services described in the latest OBD-II standard SAE J1979. Before 2002, J1979 referred to these services as “modes”. They are as follows:

Service (hex) Description
0x01Show current data
0x02Show freeze frame data
0x03Show stored Diagnostic Trouble Codes
0x04Clear Diagnostic Trouble Codes and stored values
0x05Test results, oxygen sensor monitoring (non CAN only)
0x06Test results, other component/system monitoring (Test results, oxygen sensor monitoring for CAN only)
0x07Show pending Diagnostic Trouble Codes (detected during current or last driving cycle)
0x08Control operation of on-board component/system
0x09Request vehicle information
0x0APermanent Diagnostic Trouble Codes (DTCs) (Cleared DTCs)

The vehicle manufacturers are not required to support all services. Each manufacturer may define additional services above #9 (e.g.: service 22 as defined by SAE J2190 for Ford/GM, service 21 for Toyota) for other information e.g. the voltage of the traction battery in a hybrid electric vehicle (HEV).


Mode-1 Pids: Mode 1 is used to know the current value of the corresponding PID. Mode 2 is used to know the state of the PIDs when a fault is detected.

0000List of PIDs supported (range 01 to 32)
0101Status since the last clearing of fault codes
0202Fault code that caused the recording of “freeze frame” data
0303Fuel system status
0404Engine load calculated in %
0505Temperature of the engine coolant in °C
0606Short-term fuel % trim bank 1
0707Long-term fuel % trim bank 1
0808Short-term fuel % trim bank 2
0909Long-term fuel % trim bank 2
0A10Fuel pressure in kPa
0B11Intake manifold absolute pressure in kPa
0C12Engine speed in rpm
0D13Vehicle speed in kph
0E14Timing advance on cylinder 1 in degrees
0F15Intake air temperature in °C
1016Air flow measured by the flowmeter in g/s
1117Throttle position in %
1218Status of the secondary intake circuit
1319O2 sensor positions bank/sensor
1420Oxygen sensor volts bank 1 sensor 1/td>
1521Oxygen sensor volts bank 1 sensor 2
1622Oxygen sensor volts bank 1 sensor 3
1723Oxygen sensor volts bank 1 sensor 4
1824Oxygen sensor volts bank 2 sensor 1
1925Oxygen sensor volts bank 2 sensor 2
1A26Oxygen sensor volts bank 2 sensor 3
1B27Oxygen sensor volts bank 2 sensor 4
1C28OBD computer specification
1D29O2 sensor positions bank/sensor
1E30Auxiliary input status
1F31Run time since engine start
2032List of PIDs supported (range 33 to 64)
2133Distance travelled with MIL on in kms
2234Relative fuel rail pressure in kPa
2335Fuel rail pressure in kPa
2436O2 sensor (extended range) bank 1, sensor 1 (lambda and volts)
2537O2 sensor (extended range) bank 1, sensor 2 (lambda and volts)
2638O2 sensor (extended range) bank 1, sensor 3 (lambda and volts)
2739O2 sensor (extended range) bank 1, sensor 4 (lambda and volts)
2840O2 sensor (extended range) bank 2, sensor 1 (lambda and volts)
2941O2 sensor (extended range) bank 2, sensor 2 (lambda and volts)
2A42O2 sensor (extended range) bank 2, sensor 3 (lambda and volts)
2B43O2 sensor (extended range) bank 2, sensor 4 (lambda and volts)
2C44EGR in %
2D45EGR error in %
2E46Evaporation purge in %
2F47Fuel level in %
3048Number of warning(s) since faults (DTC) were cleared
3149Distance since faults (DTC) were cleared.
3250Evaporation system vapour pressure in Pa
3351Barometic pressure in kPa
3452O2 sensor (extended range) bank 1, sensor 1 (lambda and volts)
3553O2 sensor (extended range) bank 1, sensor 2 (lambda and volts)
3654O2 sensor (extended range) bank 1, sensor 3 (lambda and volts)
3755O2 sensor (extended range) bank 1, sensor 4 (lambda and volts)
3856O2 sensor (extended range) bank 2, sensor 1 (lambda and volts)
3957O2 sensor (extended range) bank 2, sensor 2 (lambda and volts)
3A58O2 sensor (extended range) bank 2, sensor 3 (lambda and volts)
3B59O2 sensor (extended range) bank 2, sensor 4 (lambda and volts)
3C60Catalyst temperature in °C bank 1, sensor 1
3D61Catalyst temperature in °C bank 2, sensor 1
3E62Catalyst temperature in °C bank 1, sensor 2
3F63Catalyst temperature in °C bank 2, sensor 1
4064List of PIDs supported (range 65 to 96)
4165Monitor status this drive cycle
4266Control module voltage in V
4367Absolute engine load
4468Equivalent fuel/air mixture request
4569Relative throttle position in %
4670Ambient air temperature in °C
4771Absolute throttle position B in %
4872Absolute throttle position C in %
4973Accelerator pedal position D in %
4A74Accelerator pedal position E in %
4B75Accelerator pedal position F in %
4C76Commanded throttle actuator in %
4D77Engine run time since MIL on in min
4E78Engine run time since faults cleared in min
4F79Exteral test equipment no. 1 configuration information
5080Exteral test equipment no. 2 configuration information
5181Fuel type used by the vehicle
5282Ethanol fuel %
5383Absolute evaporation system vapour pressure in kPa
5484Evaporation system vapour pressure in Pa
5585Short-term O2 sensor trim bank 1 and 3
5686Long-term O2 sensor trim bank 1 and 3
5787Short-term O2 sensor trim bank 2 and 4
5888Long-term O2 sensor trim bank 2 and 4
5989Absolute fuel rail pressure in kPa
5A90Relative accelerator pedal position in %
5B91Battery unit remaining life (hybrid) in %
5C92Engine oil temperature in °C
5D   93Fuel injection timing in °
5E94Fuel consumption in litre/hr
5F95Fuel consumption in litre/hr
6096List of PIDs supported (range 97 to 128)
6197Driver demand: torque percentage (%)
6298Final engine torque percentage (%)
6399Engine torque reference in Nm
64100Engine torque data in %
65101   Auxiliary inputs / outputs
66102Flowmeter sensor
       67103     Engine water temperature in °C
68104Air temperature sensor in °C
69105Commanded EGR and EGR error
6A106Commanded Diesel intake air flow control and relative intake air flow position
6B107Recirculation gas temperature in °C
6C108Commanded throttle actuator control and relative throttle position
6D109Fuel pressure control system
6E110Injection pressure control system
6F111Turbocharger compressor inlet pressure in kPa
70112Boost pressure control in kPa
71113Variable Geometry turbo (VGT) control
72114Wastegate control
73115Exhaust pressure in kPa
74116Turbocharger RPM
75117Turbocharger A temperature in °C
76118Turbocharger B temperature in °C
77119Charge air cooler temperature in °C
78120Exhaust Gas temperature (EGT) Bank 1
79121Exhaust Gas temperature (EGT) Bank 2
7A122Diesel particulate filter (DPF) bank 1
7B123Diesel particulate filter (DPF) bank 2
7C124Diesel Particulate filter (DPF) temperature
7D125NOx NTE control area status
7E126PM NTE control area status
7F127Engine run time
80128List of PIDs supported (range 129 to 160)


0000List of PIDs supported (range 01 to 32)
0101Rich to lean sensor threshold voltage
0202Lean to rich sensor threshold voltage
0303Low voltage used to calculated passage time
0404High voltage used to calculated passage time
0505Rich to lean calculated passage time
0606Lean to rich calculated passage time
0707Minimum sensor voltage during test cycle
0808Maximum sensor voltage during test cycle
0909Time between sensor transitions
0A10Sensor period
0B11Reserved for future use

OBD-II:  The OBD-II is still a concept, is an advancement over OBD-II which will be equipped with telemetry. Using a radio transponder, OBD-III equipped vehicles will be able to send emissions problems directly to the regulating authority. It will report the Vehicle Identification Number (VIN) and the DTC. This can be done via cellular or satellite link as soon as the MIL turns on. This will help in cost savings as only vehicles with emission problems need to be tested.

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