Auto diagnostics, what is it?

What do the modern car diagnostics mean?

Currently cars are being equiped with electronic control units responsible not only for the engine but providing many other functions; therefore causes of possible failures are much easier to determine. Most of the control units have a function called 'memory of defects' that saves all the previous defects and failures. This functions allows the user to determine and solve even very rare failures difficult tootherwise pinpoint. In case of a more serious defect a yellow engine control light "MIL" will automaticaly switch on on the dash board. This control lamp will be switched off only after the problem is corrected.

With the help of a diagnostic plug in your car you can hook up to the individual control system units through a computer with a special program previously installed or through special diagnostic equipment. This equipment allows you to read information about possible failures in your car, set up or read different values, etc. and all these functions can be performed even when the car is running.

Diagnostic standards OBD, OBD2 (OBD II, EOBD)

Considering the number of car producers, for quite a while there was no widely acknowledged diagnostics standard. Therefore each producer held its own standard. This diagnostic function, not responding to any international standard, is collectively and not very precisely, called OBD or OBD I.

In the 90's the standard called OBD II (On board diagnostics) was generaly approved.

Different implementation of the engine control lights MIL

Its main purpose is to establish a unified system for automobile diagnostics that will ensure the diagnostics on its own. It is able to discover a failure and inform the driver by switching on a yellow MIL control button or "Check Engine" button or "Engine ready for a check up" button.

As a consequence the original American standard called OBDII was taken over by the European statute under the name EOBD (European onboard diagnostics). American vehicles have had to fulfil OBDII since 1996, European gasoline vehicles since 2000, and diesel vehicles since 2003. The majority of producers, however, established EOBD in their vehicles even before these dates, as well the Asian car producers. Sometimes you can find the Japanese version of EOBD called JOBD.

Vehicles produced under the OBDII standard have a standardized connector 'SAE-J1962' (see picture), situated close to the driver`s seat (usually on the bottom side of the dash-board or on its middle section).

Connector OBD II

Plugging: 2 J1850 PWM Bus + or J1850 VPW Bus 4 body of the car 5 communication bodykomunikační kostra 6 CAN-Bus High (J2284) 7 communication line K-line (ISO 9141-2) 10 J1850 PWM Bus - 14 CAN-Bus Low (J2284) 15 initialization line L-line or 2. K-line (ISO 9141-2) 16 palubní napětí +12V

Be CAREFUL! This connector is sometimes used even in older vehicles not compatible with the OBDII standard. Therefore finding this kind of connector in your car does not mean your car is OBDII compatible.

To make things a bit more complicated there are three, or if you like, four different versions of hardware protocols for OBDII. First is ISO9141, or ISO14230=KWP2000 (ISO) used by all Europeans, most Japanese, and some American vehicles (DaimlerChrysler for example). Then SAE-J1850-VPW (Variable Pulse Width, VPW) used by General Motors and DaimlerChrysler and SAE-J1850-PWM(Variable Pulse Modulation PWM) used by Ford. The fourth alternate is a totally different hardware interface "CAN" (Controller Area Network, ISO15765) used in the most modern cars, often with the "old" interface ISO. American vehicles will have had this version obligatory from 2008.

ISO9141-2	4)body, 5)communication body 7)K-Line, 15)L-Line/2.K-Line*, 16)+12V
ISO14230	4)body, 5)communication body 7)K-Line, 15)2.K-Line*, 16)+12V
J1850 VPW	2)Bus, 4)body, 5)communication body 16)+12V (pin 10 is not plugged in)
J1850 PWM	2)Bus+, 4)body kostra, 5)communication body 10)Bus- 16)+12V
CAN BUS (J2284)	4)body 5)communication body 6)CAN-Bus High 16)+12V

I own a: Škoda, Volkswagen, Audi, Seat

In our geographical latitudes people most often own cars produced by the VW concern. The modern diagnostics have been supported in these cars since the end of the eighties. In the beginning producers used to put the diagnostic plug in the engine space, later they moved it to the cockpit.

From the middle of the 90's the diagnostic connector 2x2 with two 2pin plugs was used. VW LT cars used a special round connector and Skoda-Favorit cars and the first series of Skoda-Felicia cars had their own flat connector. Skoda Felicia 95 was the first model with a standard 16pin OBD II connector J1962 (see above).

Connector 2x2 used in older VW/AUDI cars

For the diagnostics of VW concern vehicles a standard connecting cable (ISO9141, ISO14230) is being used. Above this standard there is another communication built on KWP 1280 protocoles and KWP 2000 in newer cars. In any case we can say that a specific diagnostics standard used by VW concern is actually richer than the unified OBDII and therefore provides its users wider use options.

In branded service diagnostic equipment VAG 1552, VAS 1551 or more modern VAS 50501 and VAS 5052 are used.

OBD II / VAG-COM cable

And now you can do the same with a simple PC, connection cable, and a special program. One of the most popular and perfect programs is VAG-COM produced by ROSS-TECH. Links to this and other popular programs are named in the software section .

Another option for useing diagnostics for a VW car is the diagnostic equipment CarTOOL VAG which is able to read failure numbers from the failure memory, show them on the display and erase them at your request. This equipment does not require any PC or special cables- you will simply connect CTOOLS to the diagnostic connector of your car. Another advantage of this program is its low price. Compared to the VAG-COM program CarTOOL VAG offers less functions. But, if you want equipment that will find an error and erase it from the error memory then CarTOOL VAG is fully sufficient for you. CarTOOL VAG is able to diagnose the control units of the engine, gear-box, ABS and airbags.

I own another type of car

For cars other than VW we have diagnostic equipment 'CarTOOL OBD II' able to run diagnostics in cars compatible with the OBD II standard. In case you are not one-hundred per cent sure whether your vehicle is compatible with the OBD II standard, keep reading:

1. Check out whether your car has a standard 16pin OBD II connector
2. In case you own an American vehicle, check out whether there is a label 'OBD II certified' on the engine of your vehicle.
3. In case you do not have this label but you do own an American vehicle produced after 1996, it is highly possible that your car is OBD II compatible.
4. In case you own a European or Asian car with a gasoline engine produced after 2000 and you found a standard 16ti pin OBD II connector, it is highly possible that your car is OBD II compatible.
5. In case you own a European or Asian vehicle with a diesel engine produced after 2003 and you found a standard 16ti pin OBD II connector, it is highly possibe that your car is OBD II compatible.
6. Even in case you do not find the OBD II connector and your car does not respond to any of previously named, there is a good chance that your car is OBD II compatible. If you want to be one-hundred per cent sure, try some of the OBD II diagnostics equipment (CarTOOL, diagnostic cable)

Label OBD II