[a4anurag]

What is OBD?

OBD stands for “On-Board Diagnostics.” It is a computer-based system originally designed to reduce emissions by monitoring the performance of major engine components.

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 kinds of on-board diagnostic systems: OBD-I and OBD-II.

OBD - 1

OBD-1 Refers to the first generation OBD systems which were developed throughout the 1980s. These early systems use proprietary connectors, hardware interfaces, and protocols. A mechanic who wanted to access 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.

OBD - 2

In the early 1990s, Society of Automotive Engineers (SAE) and International Standardization Organization (ISO) issued a set of standards which 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 was first introduced in model year (MY) 1994 vehicles, and became a requirement for all cars and light trucks starting with MY1996.



----------------------------------------------------------------------------------------------------------------------------------------------------

How do I know whether my car is OBD-II compliant?

There are several ways.
1996 or newer model year vehicle sold in the United States

United States legislation requires all cars and light trucks model year (MY) 1996 and newer to be OBD-II compliant. More information is available on the EPA's website.
2001 or newer model year gasoline vehicle sold in the European Union

Commission Directive 70/220/EEC, Annex I:

8.1. Vehicles with positive-ignition engines
With effect from 1 January 2000 for new types and from 1 January 2001 for all types, vehicles of category M1, except vehicles the maximum mass of which exceeds 2500 kg, and vehicles of category N1 class I, must be fitted with an on-board diagnostic (OBD) system for emission control in accordance with Annex XI.

Note that here "European Union" means countries which were members of the EU in 2000.

2004 or newer model year diesel vehicle sold in the European Union

Commission Directive 70/220/EEC, Annex I:

8.2. Vehicles with compression-ignition engines
Vehicles of category M1, except
- vehicles designed to carry more than six occupants including the driver,
- vehicles whose maximum mass exceeds 2500 kg,
from 1 January 2003 for new types and from 1 January 2004 for all types, must be fitted with an on-board diagnostic (OBD) system for emission control in accordance with Annex XI.

Note that here "European Union" means countries which were members of the EU in 2003.

Other vehicles

If your vehicle does not fall into any of the above categories, look under the hood and try to locate a label (Fig. 1) that explicitly states that the vehicle was designed to comply with OBD-II legislation.



Fig. 1 - Vehicle Emission Control Information Label

In this case, OBD-II is used as a general term and can mean any of the following:

OBD II (California ARB)
EOBD (European OBD)
JOBD (Japanese OBD)

You may also consult your vehicle's owner's manual and perhaps contact your local dealer. However, be aware of the fact that many dealers do not know the difference between OBD and OBD-II.

If the vehicle is not OBD-II compliant, you cannot use a generic OBD-II scan tool such as ElmScan to obtain diagnostic information from your vehicle.

But my car has the 16-pin OBD connector, shouldn't it be OBD-II compliant?

No, not necessarily. A lot of European and Asian manufacturers equipped their vehicles with D-shaped 16-pin connectors long before they began installing OBD-II systems on those vehicles. One curious thing to note here is the fact that most non-EOBD compliant vehicles had a DLC that does not fully conform to SAE J1979. Compare figures 2 and 3, and notice the "ears" on the non-EOBD compliant Ford Focus.



Fig. 2 - Ford Escort DLC



Fig. 3 - J1962 Vehicle Connector, Type A

----------------------------------------------------------------------------------------------------------------------------------------------------

Which OBD-II protocol is supported by my vehicle?

All cars and light trucks built for sale in the United States after 1996 are required to be OBD-II compliant. The European Union OBD legislation is somewhat more complicated.

An OBD-II compliant vehicle can use any of the five communication protocols: J1850 PWM, J1850 VPW, ISO9141-2, ISO14230-4 (also known as Keyword Protocol 2000), and more recently, ISO15765-4/SAE J2480 (a "flavor" of CAN). US car manufacturers were not allowed to use CAN until model year 2003, but as of model year 2008 and going forward, all vehicles will use the CAN protocol.

There are two types of diagnostic link connectors (DLCs) defined by SAE J1962 - Type A and Type B, shown in Figures 2 and 3, respectively. The main difference between the two connectors is in the shape of the alignment tab.

Location - According to J1962, Type A DLC "shall be located in the passenger or driver's compartment in the area bounded by the driver's end of the instrument panel to 300 mm (~1 ft) beyond the vehicle centerline, attached to the instrument panel and easy to access from the driver's seat. The preferred location is between the steering column and the vehicle centerline."



Fig. 1 - J1962 Vehicle Connector, Type A

Type B DLC "shall be located in the passenger or driver's compartment in the area bounded by the driver's end of the instrument panel, including the outer side, and an imagined line 750 mm (~2.5 ft) beyond the vehicle centerline. It shall be attached to the instrument panel and easy to access from the driver's seat or from the Co-drivers seat or from the outside. The vehicle connector shall be mounted to facilitate mating and unmating."



Fig. 2 - J1962 Vehicle Connector, Type B

As a general rule, you can determine which protocol your vehicle is using by looking at the pinout of the DLC:



Fig. 3

The following table explains how to determine the protocol:



*Pin 15 (also called the "L-line") is optional in newer vehicles that use the ISO9141-2 or ISO14230-4 protocols.

In addition to pins 2, 7, 10, and 15, the connector should have pins 4 (Chassis Ground), 5 (Signal Ground), and 16 (Battery Positive). This means that:



The following image gives the meaning of the 16 pins in the OBD - II connector.



Source:

http://www.obdsol.com/articles/on-bo...s/what-is-obd/

https://www.scantool.net/support/ind...icleid=2&nav=0

https://www.scantool.net/support/ind...icleid=3&nav=0

MODS: There are a few threads on OBD. Didn't understand where to post this information. So please move it to the right thread or a new thread altogether for discussions further.

Cheers,
Anurag.

[GTO]

Thread moved from the Assembly Line to Technical Stuff. Thanks for sharing!

[a4anurag]

Decoding the OBD -II code

OBD-II codes consist of a number of parts.

Here is a sample OBD2 Code: P0171. Here is a breakdown of what each digit of the code means:

First Character - System

The first character identifies the system related to the trouble code.
P = Powertrain;
B = Body;
C = Chassis;
U = Undefined

Second Digit - Code Type

The second digit identifies whether the code is a generic code (same on all OBD-II equipped vehicles), or a manufacturer specific code.

0 = Generic (this is the digit zero -- not the letter "O")
1 = Enhanced (manufacturer specific)

Third Digit - Sub-System

The third digit denotes the type of sub-system that pertains to the code

1 = Emission Management (Fuel or Air)
2 = Injector Circuit (Fuel or Air)
3 = Ignition or Misfire
4 = Emission Control
5 = Vehicle Speed & Idle Control
6 = Computer & Output Circuit
7 = Transmission
8 = Transmission
9 = SAE Reserved
0 = SAE Reserved

Fourth and Fifth Digits

These digits, along with the others, are variable, and relate to a particular problem.

For example, a P0171 code means P0171 - System Too Lean (Bank 1).

http://www.obd-codes.com/faq/obd2-codes-explained.php

------------------------------------------------------------------------

What OBD-II Protocols Are There?

There are five different OBD-II communication protocols:

1) J1850 PWM
2) J1850 VPW
3) ISO9141
4) ISO14230 (also known as Keyword Protocol 2000)
5) CAN (ISO15765 / SAEJ2480)

-------------------------------------------------------------------------

The most common OBD-II codes are:

P0 xxx - Powertrain codes;

B xxxx - B Codes - OBD-II Body Codes;

C xxxx - C Codes - Chassis Codes and

P1xxx, that means it's a manufacturer specific code.

http://www.obd-codes.com/trouble_codes/

-------------------------------------------------------------------------

P0 xxx - Powertrain codes;

The following are the main code headings having many individual codes for each malfunction recorded.

P0001-P0099 - Fuel and Air Metering and Auxiliary Emission Controls
P0100-P0199 - Fuel and Air Metering
P0200-P0299 - Fuel and Air Metering (Injector Circuit)
P0300-P0399 - Ignition System or Misfire
P0400-P0499 - Auxiliary Emissions Controls
P0500-P0599 - Vehicle Speed Controls and Idle Control System
P0600-P0699 - Computer Output Circuit
P0700-P0899 - Transmission

The detailed codes are found here:

http://www.obd-codes.com/trouble_codes/

--------------------------------------------------------------------------

B - OBD-II Body Codes

These are the generic OBD-II Body Codes. They all begin with B0.

Examples of OBD-II body trouble codes include:
Side Airbag Deployment Control
Frontal Stage 1 Deployment Control
Seatbelt Pretensioner Deployment Control
Seatbelt Load Limiter Deployment Control
Side Restraints Sensor
Driver Seat Recline Position Restraints Sensor
Passenger Seat Occupant Classification Sensor

--------------------------------------------------------------------------

C - Generic OBD-II Chassis Codes

http://www.obd-codes.com/trouble_cod...ssis-codes.php

[a4anurag]

In my previous post I had mentioned the types of protocols being used. Here is a small brief in them.

An OBD2 compliant vehicle can use any of the five communication protocols:

1) SAE J1850 PWM,
2) SAE J1850 VPW,
3) ISO9141-2,
4) ISO14230-4 (KWP2000), and
5) ISO 15765-4/SAE J2480 (since 2003)

Please note that some models are equipped with SAE J1962 connector, but these cars are NOT OBD2 compliant. Typical examples of such cars are some early VW/Skoda/Seat models (European versions only), Ford cars with EEC-IV using Ford DCL protocol (e.g. Ford Escort), Nissan EU/Asian models (using Nissan DDL protocol), or some European Hyundai models.

ISO15765-4 (CAN-BUS)

The most modern protocol, mandatory for all 2008+ vehicles sold in the US. Uses pins 6 and 14, communication is differential. Four variants of ISO15765 exist. They differ only in identifier length and bus speed:

-> ISO 15765-4 CAN (11 bit ID,500 Kbaud)
-> ISO 15765-4 CAN (29 bit ID,500 Kbaud)
-> ISO 15765-4 CAN (11 bit ID,250 Kbaud)
-> ISO 15765-4 CAN (29 bit ID,250 Kbaud)
-> ISO14230-4 (KWP2000)

Very common protocol for 2003+ vehicles using ISO9141 K-Line. Uses pin 7.
Two variants of ISO14230-4 exist. They differ only in method of communication initialization. All use 10400 bits per second.

ISO 14230-4 KWP (5 baud init,10.4 Kbaud)
ISO 14230-4 KWP (fast init,10.4 Kbaud)
ISO9141-2

Older protocol used mostly on European vehicles between 2000 and 2004. Uses pins 7 and optinally 15.

SAE J1850 VPW

Diagnostic bus used mostly on GM vehicles. Uses pin 1, communication speed is 10.4 kB/sec.

SAE J1850 PWM

Diagnostic bus/protocol used mostly on Ford. Uses pins 1 and 2, communication signal is differential and it's rate is 41.6kB/sec.

They usually connect to other (non-engine) ECUs or provide various signals. Generic OBD2 tools are not capable of "talking" to other ECUs than engine. For diagnosis of other control units such as ABS, airbag, audio or body modules you need vendor-specific software such as FiCOM (Fiat/Alfa/Lancia), FoCOM (Ford/Mazda) or HiCOM (Hyundai/Kia).

Other non-OBD2 protocols

Almost every car uses also vendor-specific diagnostic protocols such as KWP2000, KW1281, VWTP, KW72, KW82, which are used for "native" diagnostics.

Source: http://www.obdtester.com/obd2_protocols

[a4anurag]

A few parameters and their meaning for easier understanding.

Calculated Load:

Range: 0 to 100 %

Technically, calculated load is current airflow divided by peak airflow, where peak airflow is corrected for altitude (barometric pressure). Peak airflow is typically represented as the maximum theoretical airflow possible or is calculates as a function of engine RPM.

Load = (Current Airflow / (peak airflow @ sea level))*(Sea level atmospheric pressure/Barometric pressure)*100%

Basically it's exactly as its labelled. It tells you how much load is on the engine. In super simple terms its throttle position corrected for RPM, gravity (hill) and drag (wind, rolling resistance).

Oxygen Sensor Bank X Sensor Y:

Range (sensor): 0 to 1.27 volts
Range (trim): -100 to +99%

Each O2 sensor returns two numbers. The value of the O2 sensor and the ECU's internal O2 Trim for that sensor. The O2 Volts is an indication of air/fuel ratio as measured from the O2 sensor. In closed loop mode, the ECU uses this sensor as its feedback sensor to base any fuel trim adjustments.
The O2 Trim is a trim for that sensor which allows the ECU to compensate for differences in sensors. Trims that are abnormally high or low ‘can’ be an indication of a bad O2 sensor. O2 sensor values are ignored in open loop mode.

The Bank number indicates what group of cylinders the sensor is measuring. Bank 1 always contains cylinder 1. Inline motors typically only have one bank. V motors have two. The sensor number indicates how far the sensor is downstream. Sensor 1 is always closest to the cylinder head and count up from there.

Throttle Position:

Range: 0 to 100%

The position of the Throttle Position Sensor (TPS) on the throttle body. The % should directly correlate to the gas pedal position. This is an absolute value based on a 0 to 5 volt sensor output. Meaning on 99% of cars out there, the value will never reach 0 or 100% because the throttle will hit mechanical stops before reaching the full travel of the sensor. The ECU typically uses the TPS to sense changes in throttle, not a particular throttle position. When the ECU senses a positive change in throttle position, extra fuel is injected, much like the accelerator pump on carburettors. If the signal jumps around (usually happens at a single throttle position, but can happen at any time) then you could have a bad TPS sensor. This would cause bucking or hesitation while driving.

Long Term Fuel Trim Bank X:

Range: -100 to +99%
Bank: 1 or 2

Fuel Trims are correction factors applied to the base fuel map. When in closed loop mode, the O2 Sensor is used to adjust the trims based on the sensor's values. A positive trim indicates the ECU is adding fuel (a lean condition), and a negative trim indicates the ECU is taking away fuel (a rich condition) from the base fuel map. Fuel trims are not used in open loop mode. Long Term fuel trims differ from Short Term trims in that Long Term trims are stored between starts and they change more slowly. If there is a trend in a short term trim, eventually the long term trim will adjust to move the short term trim back to zero. This allows the ECU to adjust its fuel map to compensate for variances in sensors or dirty injectors, etc. The Bank indicates a group of cylinders. Inline motors typically have 1 bank. V motors have two banks. Typically there is an O2 sensor for each Bank and that is the sensor the trims use to adjust themselves. Bank 1 always contains cylinder number 1. Trim values are useful for part throttle tuning of S-AFC (or similar) fuel computers.

Short Term Fuel Trim Bank X:

Range: -100 to +99%
Bank: 1 or 2

Fuel Trims are correction factors applied to the base fuel map. When in closed loop mode, the O2 Sensor is used to adjust the trims based on the sensor's values. A positive trim indicates the ECU is adding fuel (a lean condition), and a negative trim indicates the ECU is taking away fuel (a rich condition) from the base fuel map. Fuel trims are not used in open loop mode. Short Term fuel trims differ from Long Term trims in that Short Term trims are not stored between starts and they change more frequently. If there is a trend in a short term trim, eventually the long term trim will adjust to move the short term trim back to zero. This allows the ECU to adjust its fuel map to compensate for variances in sensors or dirty injectors, etc. The Bank indicates a group of cylinders. Inline motors typically have 1 bank. V motors have two banks. Typically there is an O2 sensor for each Bank and that is the sensor the trims use to adjust themselves. Bank 1 always contains cylinder number 1. Trim values are useful for part throttle tuning of S-AFC (or similar) fuel computers.

PS: I am not able get the source of the PDF file that I had downloaded. Will post the source in case I get it.

Anurag.

[ecosport rules]

Originally Posted by a4anurag

In my previous post I had mentioned the types of protocols

Hey anurag ,
This is a supremely informative thread.
Amazing compilation.

Ive recently installed the torque pro software and ordered one OBD 2 reader.
Will share more info once I receive it.

Thanks for sharing your effort.

[a4anurag]

Originally Posted by ecosport rules

Hey anurag ,
This is a supremely informative thread.
Amazing compilation.

Ive recently installed the torque pro software and ordered one OBD 2 reader.
Will share more info once I receive it.

Thanks for sharing your effort.

Thanks buddy.

Have you tried using the ELM 327 OBD II reader on your car before purchase?

What kind of reader and from where have you bought it?

Anurag.

[ecosport rules]

Originally Posted by a4anurag

Thanks buddy.

Have you tried using the ELM 327 OBD II reader on your car before purchase?

What kind of reader and from where have you bought it?

Anurag.

This is the one I have ordered from Aliexpress.com.
I have never used it on any of my cars before.

[SirAlec]

i am planning to write an article on this. I have ordered a OBD scanner from a fellow bhpian, but its sitting duck since three months.

Time is what i am lacking right now.

[n_aditya]

Excellent thread Anurag. Rated 5 stars.

[audioholic]

Originally Posted by ecosport rules

This is the one I have ordered from Aliexpress.com.
I have never used it on any of my cars before.

Let me know if you receive the product safely and it works. Need a couple of them for a project. From the reviews of ali express, I am hesitant to order from them since you cam get the same from Ebay for slightly higher.

[a4anurag]

Originally Posted by audioholic

Let me know if you receive the product safely and it works. Need a couple of them for a project. From the reviews of ali express, I am hesitant to order from them since you cam get the same from Ebay for slightly higher.

Hi buddy.

If you need my OBD II Reader please PM me your address. I'll be happy to send it for your project work. I use it but not to frequent so it is idle sometimes. Will be happy if it if use to you.

Anurag.

[devrajman]

Great Thread! Next will be to have a table with majority of cars in market and OBDII protocol used by them and may be even PIDs supported!

I too have all kinds and varieties of ELM327 and also standalone scanners and will be happy to help anyone on project.

Also have OBDII Readers with inbuilt GPS & GSM for remote monitoring.

[audioholic]

Originally Posted by a4anurag

Hi buddy.

If you need my OBD II Reader please PM me your address. I'll be happy to send it for your project work. I use it but not to frequent so it is idle sometimes. Will be happy if it if use to you.

Anurag.

Hi Anurag
Thanks a ton for the offer. We already have a few with us, to be exact four of them. Will need some more. However, do retain yours with you. I will require a different kind of help from you in a few weeks of time. Hence the device is better kept with yourselves. Will let you know when help is required .
Thanks again.

[a4anurag]

Originally Posted by audioholic

Hi Anurag
Thanks a ton for the offer. We already have a few with us, to be exact four of them. Will need some more. However, do retain yours with you. I will require a different kind of help from you in a few weeks of time. Hence the device is better kept with yourselves. Will let you know when help is required.
Thanks again.

Done buddy.

Just ping me and I shall be of help as much as I can.

Anurag.