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README.OBD2
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README.OBD2
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README.OBD2
-----------
* OBD2 basics
* What is OBD2?
* What is the purpose of an OBD2 scan tool?
* What are other uses of the OBD2 interface?
* How does one connect to the OBD2 system in a vehicle?
* Engine basics
* What is Electronic Fuel Injection (EFI)?
* What kind of emmissions control systems are present in vehicles?
* Catalyst (Catalytic Coverter) / Heated
* Evaporative (Evap) System
* Secondary Air
* A/C Refrigerant
* Oxygen Sensor / Heated
* Exhaust Gas Recirculation (EGR) system
* OBD2 details
* How does OBD2 work?
* What are the PIDs used with OBD2?
* What do I do with a Diagnostic Trouble Code (DTC)?
* What are OBD2 monitors?
OBD2 basics
-----------
* What is OBD2?
On-Board Diagnostics, second generation.
The OBD2 standard is a legal requirement for all cars sold in the US since
1996. The standard is primarily a means for monitoring and reducing vehicle
emmissions, but is also useful for interacting with the engine computers in
modern vehicles.
http://en.wikipedia.org/wiki/On-board_diagnostics#OBD-II
* What is the purpose of an OBD2 scan tool?
At it's simplest, an OBD2 scan tool is used to "pull the codes" from a car
that has a "Check Engine" light turned on. These codes tell you what's
wrong with the car so you can correct it.
Additionally, state-mandated emmissions inspections use an OBD2 scan tool
to retrieve the status of several emmissions monitors.
* What are other uses of the OBD2 interface?
Manufacturers and repair shops also use the same OBD2 interface to
connect their advanced diagnostic equipment. Though only the standard
OBD2 command and response functions are mandated to be present,
manufacturers typically also make the core vehicle sensor network
accessible through the same connector.
Also, OBD2 dataloggers that record sensor info can be used for:
- driving habits analysis/monitoring
- correlation with GPS info
- engine tuning
- virtual dashboard
* How does one connect to the OBD2 system in a vehicle?
There is a standard connector located under the console near the driver. An
OBD2 reader device hooks up to this port and converts the vehicle network to
either RS-232, USB, or bluetooth. Information is gathered by sending short
commands and receiving back the corresponding information.
Engine basics
-------------
* What is Electronic Fuel Injection (EFI)?
An engine needs fuel to run. Old vehicles used a carburetor to add fuel to
the air entering the engine. Instead of a carburetor, modern vehicles use
Fuel Injectors, controlled by a computer. The computer uses several sensors
throughout the vehicle to determine the proper amount of fuel to inject.
Primer on EFI Theory:
http://www.sdsefi.com/techtheo.htm
More EFI info, by a rally driver:
http://www.innovatemotorsports.com/resources/ecu-basics.php
Lots of EFI related info:
http://autoshop101.com/
The OBD2 standard requires the engine computer to monitor the status of
emmission control subsystems and report when they fail.
* What kind of emmissions control systems are present in vehicles?
* Catalyst (Catalytic Coverter) / Heated
Many byproducts of combustion can be eliminated by passing the exhaust stream
across a surface covered with catalysts that help convert harmful emmissions
into less harmful emmissions. Most catalysts work at specfic temperatures.
Unheated catalysts can work poorly or not at all. The exhaust is hot enough
to heat up the catalytic converter, but some may have an electric heating
element to help it heat up faster after a cold start.
* Evaporative (Evap) System
Evaporated fuel is a major source of emmissions. Modern vehicles have a
sealed and pressurized fuel tank with a charcoal canister that collects
evaporated fuel and later "purges" it back to the fuel system. Additionally,
a Positive Crankcase Ventilation (PCV) subsystem can recover fuel vapors that
slip past the piston rings into the crankcase.
* Secondary Air
Primary Air would be the air used in combustion in the engine. Secondary Air
is the injection of additional air into the exhaust to help combust any fuel
that remains in the exhaust. It can be injected upstream or downstream of the
catalytic converter. The secondary air injector is sometimes called a smog
pump. This is an old technique for emmissions control and is not common on
new vehicles.
* A/C Refrigerant
The R-12 refrigerant formerly used by air conditioning systems readily
evaporates and is a harmful emmission. Modern vehicles don't use R-12.
Vehicles that did needed to closely monitor the A/C system for leaks.
* Oxygen Sensor / Heated
Oxygen (O2) sensors measure the oxygen content of the exhaust. Sensors could
be located upstream and/or downstream of the catalytic converter. Information
from the O2 sensors is used by the engine computer to detemine how completely
the injected fuel burned. Oxygen sensors typically work best at a particular
temperature so some have an integrated heating element.
* Exhaust Gas Recirculation (EGR) system
At high combustion temperatures, nitrogen from the atmosphere is reactive and
forms nasty emmissions. Gasoline burns hotter in the presense of excess
oxygen. This is called a "lean" fuel-to-air ratio. Excess fuel is considered
"rich." A rich fuel-air mix wastes fuel and a lean mix creates toxic
emmissions. To reduce toxic emmssions without wasting fuel, another solution
is needed. The solution is to reduce the oxygen in the mix by injecting
exhaust into the intake air stream. Since the exhaust has much less oxygen in
it, this lowers the combustion temperature.
Follow this link for an expert explaination.
http://forum.mazda6club.com/mazdaspeed6/226935-egr-systems-information.html
OBD2 details
------------
* What is the physical connector for OBD2?
SAE J1962 16-pin connector
http://pinouts.ru/connector/16_pin_car_J1962_OBD_2_special_connector.shtml
http://en.wikipedia.org/wiki/On-board_diagnostics#OBD-II_Diagnostic_connector
* How does OBD2 work?
Modes & codes.
OBD2 has 2 kinds of codes, PIDs and DTCs
* PIDs are "Parameter IDs", which is just a fancy name for command or query.
The scan tool sends a PID (eg. "0115") to the vehicle and a string of hex encoded bytes is returned
Many PIDs correspond to a particular sensor in the vehicle.
Each PID has different rules for interpreting the reply.
* DTCs are "Diagnostic Trouble Codes".
When the vehicle senses an error condition it will "set" a DTC, and possibly light up the "Check Engine" light.
Scanning for set DTCs gives a vehicle troubleshooter or inspector precise information about problems.
SAE J2012
* What are the PIDs used with OBD2?
PIDs are grouped into "modes." For example, PID "0115" means something like mode "01", parameter "15".
SAE J1979 describes ten "modes" of operation for OBD-II.
Mode
ID
(hex) Mode description
----- -----------------------
01 Show current data
02 Show freeze frame data
03 Show stored Diagnostic Trouble Codes
04 Clear Diagnostic Trouble Codes and stored values
05 Test results, oxygen sensor monitoring (non CAN only)
06 Test results, other component/system monitoring (Test results, oxygen sensor monitoring for CAN only)
07 Show pending Diagnostic Trouble Codes (detected during current or last driving cycle)
08 Control operation of on-board component/system
09 Request vehicle information
0A Permanent DTC's (Cleared DTC's)
Additional modes are defined by manufacturers.
Within each mode, different vehicles support different sets of PIDs. Only a
small number of PIDs are required to be functional on all vehicles.
Lots of detail:
http://en.wikipedia.org/wiki/OBD-II_PIDs
* What do I do with a Diagnostic Trouble Code (DTC)?
DTC code descriptions are short and cryptic, particularly if one is
unfamiliar with the many emmissions control systems in a modern vehicle.
Fortunately, several websites much more information about DTCs:
- http://www.obd-codes.com/
- http://engine-codes.com/
- http://www.kbmsystems.net/obd_fault_codes_db.asp
* What are OBD2 monitors?
To facilitate the emmissions inspection process, the OBD2 standard defines
continuous and non-continuous monitors that an engine computer must use to
monitor the status of the emmission control systems present in a vehicle.
Continuous monitors
- Misfire
- Fuel system
- Components
Non-continuous monitors (spark ignition vehicles)
- Catalyst
- Heated Catalyst
- Evaporative System
- Secondary Air System
- A/C Refrigerant
- Oxygen Sensor
- Heated Oxygen Sensor
- EGR System
More info:
http://www.deq.state.va.us/mobile/mobobdm.html