WHAT IS OBD-II?
Integrated diagnostic systems are present in most cars and trucks
today. During the 1970s and early 1980s, manufacturers began using electronic
means to monitor functions and diagnose engine problems. This was primarily to
meet EPA emissions standards. Over the years diagnostic systems have become
more sophisticated. The most recent standard is OBD-II, this standard was
introduced in the mid 90s, it controls the engine almost completely and also
monitors parts of the chassis, body, accessories and the car's control
diagnostic network.
SOME OBDII HISTORY
To combat the pollution problem in the Los Angeles basin, the state
of California required emissions control systems on automobiles of the 1966
model year. The Federal Government extended these controls nationwide in 1968.
The US Congress passed the Clean Air Act in 1970 and established
the Environmental Protection Agency (EPA). This began the publication of a
series of emissions standards and requirements for vehicle maintenance. To meet
these standards, vehicle manufacturers created electronic fuel supply and
ignition systems where sensors measure engine performance and adjust the
systems to reduce pollution. These sensors also began to be used to diagnose
the vehicle.
At the beginning there were few standards and each manufacturer had
its own systems and signals. In 1988, the Society of Automotive Engineers (SAE)
established a standard connector and set of diagnostic test signals. EPA
adapted most of the standards from SAE's diagnostic programs and
recommendations. OBD-II is an expanded set of standards and practices developed
by SAE and approved by the EPA and CARB (California Air Resources Board) for
implementation on January 1, 1996.
THE NEED FOR OBDII
The Environmental Protection Agency is
responsible for reducing "mobile emissions" from cars and trucks and
has the power to require manufacturers to build cars that meet increasingly
stringent emissions standards. Furthermore, manufacturers must maintain
automobile emission standards for the life of the vehicle. OBD-II provides a
universal inspection and diagnostic method to ensure that the car is working
within the manufacturer's specifications. While there is an argument as to the
exact standards and methodology used, the fact is that there is a need to
reduce the level of pollution, caused by vehicle emissions, in our cities, and
we have to live with these requirements.
OBD-II PROTOCOLS
There are three basic OBD-II protocols in
use, each with minor variations in the communication pattern between the
on-board diagnostic equipment and the scanner. Although there have been some
manufacturer changes between protocols in recent years, as a general rule,
Chrysler vehicles, European and Asian vehicles use the ISO 9141 protocol. GM
vehicles use the SAE J1850 VPW (variable pulse width modulation) protocol. and
Ford vehicles use SAE J1850 PWM (Pulse Width Modulation) communication
patterns.
You can also tell what protocol a car
uses by examining the connector. If the connector has a pin in position #7 and
no pin in position #2 or #10, then the car has the ISO 9141 protocol. If no pin
is present in position #7, the car uses an SAE protocol. . If there are pins in
positions #7, #2 and #10, the car can use the ISO protocol.
While there are three OBD-II electrical
connection protocols, the command set is set according to the SAE J1979
standard.
HOW DO YOU MEASURE OBD-II OUTPUT?
Pre-OBD-II cars had multiple connectors
in various locations under the dash and under the hood. All OBD-II cars have a
connector that is located in the cabin easily accessible from the driver's
seat, so that a scanner can be connected with a cable
The “Check Engine” light or MIL
The Check Engine light or MIL. It has
three types of signals
Occasional flashes show a temporary malfunction.
Permanently on if the problem is more
serious.
Constant flashing if the problem is very
serious and can cause serious damage if the engine is not turned off
immediately.
In all cases, a reading is taken from all
the sensors and stored in the vehicle's central computer.
If the fault signal is caused by a
serious problem, the MIL light will be on until the problem is resolved and the
MIL light is reset.
Intermittent faults turn on the MIL
momentarily and turn off before the problem is located. The reading from the
sensors at the time of the failure, which is stored in the computer, can be of
high value in diagnosing these problems. However, if the vehicle completes
three driving cycles without the problem reappearing, the reading is cleared.
FAULT CODE (DTC)
Fault codes are regulated by the SAE
J1979 standard and is the standard used by vehicle manufacturers today. Fault
codes consist of 5 characters, which are a letter followed by four numbers.
The first character, which is a letter,
indicates the function of the vehicle according to the following.
P - Powertrain or engine and transmission
(Powertrain)
B - Body
C - Chassis
U - Undefined
The second character indicates whether
the code is generic, defined by SAE, or specific, defined by the vehicle manufacturer.
0 – Generic for all brands and defined by
SAE.
1 – Specific defined by the vehicle
manufacturer, the code is generally different for each manufacturer.
Codes 0001 to 0999 are completely defined
by SAE. Codes from 1000 to 1999 are defined by the manufacturer and only follow
the SAE standard in format.
The third character indicates the vehicle
subsystem.
0 - The complete electronic system
1 and 2 - Combustion control
3 - Ignition system
4 - Auxiliary emission control
5 - Speed and idle control
6- ECU and inputs and outputs
7 - Transmission
The fourth and fifth characters indicate
the fault.
The following image represents what we
have described.
OBDII ERROR CODE READER
OBD2 error code readers began to be one
of the first tools that car owners began to use in recent years to diagnose
problems related to engine and transmission management due to the simplicity of
their operation, generating for the which uses important failure data.
The popularity of these code readers has
increased in recent years, having the same diagnostic connector, along with
connection protocols already pre-established in all cars to connect with the
engine computer, regardless of the brand or style. of these readers an almost
pocket-sized basic tool due to its small size.
We could never compare a code reader like
these with the famous scanners that most mechanics have, since these scanners
are more powerful tools in exploring all the control units or modules that work
in the car.
In this way, these code readers, for the
most part, limit themselves to informing us why the service engine soon or
check engine light is on (both mean the same thing), extracting the error code
that has been generated and also having the possibility of delete it, however
in almost all cases this information will only refer to the engine and
transmission.
Some code readers, in addition to
extracting and erasing the code, also allow you to see in real time the
operation of some engine sensors (not all) in addition to having frozen data
that gives us an idea of what condition the engine was in when the problem was
generated. Error code.
There are also these Bluetooth tools so
that a small interface connects to the diagnostic connector and with software
either on a computer or even on a smartphone we will have access to all this
information, making it so that even with our cell phone we can obtain a
diagnosis that indicate why the yellow check engine light stays on, some of
these applications allow you to create custom clocks for speed, rpm, engine temperature,
average consumption and much more.
FUNCTIONS OF A CODE READER.
Extract the error code.
Provide frozen data
Reading data in real time from some
sensors
Code erasing
Most are limited to engine and
transmission.
THEY WILL NOT BE ABLE TO ACCESS MOST CODES
ABS brakes
Airbags
Keys
Traction control
Electric steering
Air conditioning