VW/AUDI ENGINE/ RADIATOR COOLING FAN CONTROL MODULE

VW/AUDI ENGINE/ RADIATOR COOLING FAN & CONTROL MODULE

The radiator is an integral part of each and every VW, Audi, Skoda and Seat vehicle. Its main objective is to keep the engine oil cool which in turn keeps all the moving parts of the engine cool. Most cars have a radiator fan with a separate fan for the air conditioner however, VAG vehicles have an integrated Radiator and Condenser Fan Assembly,  as can be seen in the image below. Be that as it may, it is not a one size fits all situation. Virtually every VW, Audi, Seat and Skoda vehicle category has a slightly different fan which is very evident when looking at the different three character alphanumeric prefix and the alpha suffix in their part numbers. View the list below to see what I mean.

Radiator and Condenser Fan Assembly.  The fan on the right is 360mm in diameter
with a 4-pin main connector rated at 300W.  The fan on the left is 295mm  with a 2-pin
female connector, and rated at 200W. 

The flip side of the Radiator and Condenser Fan Assembly

Be aware that a VW Polo 9N and 6R have different fans, an Audi A3 and a Q7 have different fans, a Skoda Fabia and a Roomster have different fans, a Seat Ibiza and a Seat Leon have different fans and the same and the same goes for Passat, Golf, Beetle, Tiguan, Touran, Fox, Transporter, Jetta, etc...  Having said all that, suffice to say that all these fans are troublesome, they burn out, the fins disingrates, they go open circuit and I've even known a few to go short circuit and blow its 30 amp fuse.

VW THERMOSTATICALY CONTROLLED  RADIATOR FAN 

6Q0 959 455AF Engine type: BBX - VW POLO
6R0 959 455D  Engine Code: Polo Vento
6Q0 959 455AE Engine Code: BZG - Fabia,
6Q0 959 455AE Engine Code: BMS -  Fabia, Roomster
6Q0 959 455 N Engine Code: BNM, BAY, BNV, - VW Polo, Fox,
1K0 959 455P  Engine Code: BSE  - Audi A3
1K0 959 455N  Engine Code: BLR - Passat
1K0 959 455DH Engine Code: BMY - VW Touran
1K0 959 455P  Engine Code: BMY -VW Golf
1J0 959 455   Engine Code: AKQ - VW Golf
1K0 959 455ET Engine Code: CFG - VW Tiquan
1K0 959 455FR Engine Code  CFGB - VW Tiquan
6Q0 959 455AD Engine Code: CAYB -VW Polo
6R0 959 455   Engine Code: CFWA - Skoda
6Q0 959 455AD Engine Code: AMF - Polo, Skoda Fabia, Seat Ibiza
6E0 959 455A  Engine Code: AAA - VW Golf, Passat, Polo
7L0 959 455F  Engine Code: CBFA, CCTA - Audi Q7
8D0 959 455   Engine Code: AFB - Audi A6/A8, VW

This list is by no means complete and there are probably a few dozen more variations. These fans are made  by Brose 
(Puebla/Mexico),   Behr Hella Services GmbH (Germany), Wenzhou (Mainland China) and several other an OE manufacturer expressly for the Volkswagen Group with OEM replacement part numbers 1K0959455DT, 1K0959455CQ, 1K0959455N, 1K0959455DL, 1K0959455FE, 1K0959455FJ, etc.  These are predominantly the 300W, 4-pin main connector with 2-pin female secondary connector type, guaranteed to fit the following VW and Audi models. 

2006-2013 Audi A3

2008-2015 Audi TT

2009-2015 Audi TTS

2012-2014 Audi TTRS

2012-2012 Volkswagen Beetle (up to 3/4/2012, VIN specific)

2009-2015 Volkswagen CC

2007-2015 Volkswagen EOS

2006-2014 Volkswagen GTI

2010-2014 Volkswagen Golf

2005-2012 Volkswagen Jetta (up to 3/4/2012, VIN specific)

2006-2010 Volkswagen Passat

2012-2012 Volkswagen Passat (up to 3/4/2012, VIN specific)

2008-2008 Volkswagen R32

2006-2009 Volkswagen Rabbit

2009-2015 Volkswagen Tiguan

The 360mm Radiator fan, notice the four wires in the plug, two thick and two thin.

However, in order to avoid future problems, it is highly recommenced by the fan manufactures that the controller module should be replaced together with correct fan.  The list below are just a few of the radiator controller modules / relays that support the glut of VAG fans. These relays are  VIN specific, so please verify existing part number with the supplied part for correctness.  These contollers are manufactured in Hungary,  Brazil, and Germany. 

1H0 919 506 A -VW Golf MK2 MK3, GTI 8V
1H0 919 506 B - VW Golf MK2 / MK3 GTI 8V
1J0 919 506 G - VW Golf, Lupo, caddy, Audi A3
1J0 919 506 K - Seat Arosa, Leon, Toledo, Skoda Octavia
1J0 919 506 L -  VW, Audi, Skoda & Seat
1J0 919 506 M - Polo, etc
1J0 919 506 P -Golf MK4 , etc,
1J0 919 506 Q - Golf Mk4 GTI, etc

4 and 14 Pin radiator controller module

4 and 10 pin radiator controller module

As mentioned earlier, the fans and controllers are troublesome but the German manufactured version is a lot better and thus last much longer but it is also pricier.  Notice that the main part number on both the above images are the same except for its prefix. The real difference is that the top module has 14 contacts on its right side connector whereas the middle module has only 10 and the bottom module has only 6.  The 2 images below gives you  good idea of the variations in modules. The final image shows how these modules burn.

Main and secondary connectors with 4 and 10 pins respectively.

The secondary plug has 14 pins

This is what happens to the modules made in Hungary and Brazil.

What is an EPC light? What is an EPC warning light? What is an EPC light on Volkswagen? What Is the VW EPC Warning Light? What is the EPC light on a Volkswagen Jetta? What is EPC on a Volkswagen? What does it mean if the EPC warning light comes on in a Volkswagen? Volkswagen - EPC Warning Light, What does an EPC light on the dash of a Polo match car mean? EPC light came on and lost all power.  The EPC warning symbol came on today while driving. EPC Light and stalling. EPC light came on and can't start the engine. EPC light on, what does it mean ? EPC light and engine check light. EPC warning light. Epc light. EPC + power loss/no boost.  Do not exceed 4000 rpm  EPC light.   EPC error where the car shakes terribly.  ESP EPC & Engine Light ON.  EPC Light and Stalling. Polo bluemotion 58 plate and a yellow engine light came on. I read the manual but still not sure something to do with the exhaust?? A little help as my wife needs the car for work.2002 1.6L GOLF, EPC light on. POWER LOSS An EPC light will appear on the dash randomly whilst driving. Once it is on, there is a noticeable loss in power and it stays this way until the... volkswagon polo epc warning.step by step guide to turn light off please, preferably without visiting expensive vw garage. Have diagnostic computer to see code! EPC light came on and engine will not rev higher. I have a vw polo and the EPC warning light has come on what should i do? Orange light 03 vw polo. VW Polo Map sensor fault code idling poorly. EPC light on my dashboard 2001 vw polo. It has something to do with the engine management, retarding the power of the engine.

VW BREAKDOWNS

VW BREAKDOWNS

Virtually everyday I see at least a half a dozen of brand new cars hitching a lift to some service center. Rollsbacks are becoming pervasive and are thus trending because the days when you could manage a quick repair along the roadside is long gone. Whether you drive an older well used or brand new vehicle, breakdowns are inevitably and will happen at the most inopportune moments or at the worst possible time. Having a roadside assistance service like the AA (Automobile Association) can provide some peace of mind, especially to female drivers with infants or aging parents / grandparents on board. Somehow breakdowns seem to happen when you are smartly dressed enroute to a function of sorts or when you are late for an appointment. That's Murphy's Law for you.

VW Golf GTI with a engine sensor issue

VW Golf GTI going nowhere slowly

The most common road side problem today seems to be  cars running out of fuel, because of erroneous assumptions. Due to the recent rapid rise in fuel prices everyone is still topping up their fuel tanks based on note value rather than on litre value.  For example, R100.00 worth of fuel (8.2 litres) is not the same as asking for 20 litres of LPR fuel (R250.00). Hence drivers are judging driving distance based on the Rand value, often ignoring the fuel guage and getting stuck without fuel as a consequence, though expecting the rand value of the fuel they bought should have taken them a lot further than it actually did. 

A dead battery is another common issue, which is most susceptible in winter, especially relevant to delivery vehicles that drive short distances, starting their engine often, thus not giving the battery sufficient opportunity to charge fully. Persistent battery problems are more often than not caused by a faulty alternator regulator and is not normally repairable at the road side. I've had my alternator die on me at night while driving home from movies, and I was actually watching my headlights getting dimmer by the meter, as I drove. Fortunately I made it home before my battery ran down completely.

Then there is the clutch cable that snaps under stress,  which is normally a deal breaker because it inhibits changing gears. Once when this happened to me, I started my car whilest the transmission was in 3rd gear causing the car to lunge forward as the starter rotates. It's kinda like using the starter to propel the car forward until it starts. When my car's engine started, I managed to drive all the way home in third gear without incident.

VW Polo with a ESP and EPC issue

VW Polo enroute service centre.

A flat tyre / blowout is another roadside issue, especially if you discover the spare tyre deflated due to the duration of time it spent in the boot without being checked. The worst thing ever is not being able to loosen a wheel nut that's been air torqued by the last tyre repair place you visited. 

An overheating engine can just stress you out because the first thing that comes to mind is the possible cost of repair. An overheated engine is commonly caused by a snapped fan belt or stuck thermostat which can cause the cylinder hear gasket to blow if not detected and repaired in time. When my car's engine overheated, I was some 30 Km out of Bloemfontein on the N1, enroute Cape Town; somehow the attendant at the filling station who topped up my radiator water level didn't replace its cap.  As a consequence the
water bubbled out and with insufficient water to keep the engine cool,  the  head gasket blew and I had to stay in Bloem for 13 days. It was an expensive exercise, the cost of a deco set with head gasket, the cost of the opportunistic mechanic, and the cost of hotel accommodation and obviously food.

A not so common roadside fault is locking your keys inside the vehicle or even loosing your keys. Remember the microchip inside your key can also go faulty and is the only thing that can disable your immobilizer. If this should happen it would be worthwhile having roadside assistance because they generally have a relationship with vehicle manufactureres and authorised dealers and have access to Key Assist. 

Regular services would do your driving spirit the world of good because any worm components can be detected before they actually go faulty. On of the worst roadside breakdowns is a snapped cam belt but if checked at regular services and replaced before it breaks would save you a shed load of money. It is worthwhile keeping  a set of jumper leads and a 5L can of water in you boot as well as an empy 5L can and a funnel, just in case you run out of fuel.  A spare fan belt and a mechanical toolkit would also be beneficial as boot luggage. Get into the habit of continually looking at your instrument cluster while driving to check your guages for normality, especially oil pressure, oil level and water. Check your coolant level yourself if possible before going on any long trip, and please don't allow garage attendants check it, at least not without your supervision.  Also make sure your have a spare key. 

I've never seen two VW towed in tandem like the two Toyotas above.

Two police vehicles that needs some TLC

Looking at the two images above is a least a consolation to Volkswagen owners that it's not only VW  vehicles that seems to enjoy riding on the back of rollbacks.

Feel free to upload your VW, SKODA, SEAT & AUDI scans.


Engine Control Module, Data Bus for Comfort System, Coding, Control Module for Digital Sound Package, Control Module for Airbags, Control Module for Climatronic, Klimaanlage, Control Module in Instrument Cluster, Power Steering Control Module,  No Signal/Communication - Intermittent, Intermittent Operation, Defective - Intermittent, Open Circuit — Intermittent, Short to Ground — Intermittent, Open or Short to Plus — Intermittent, Implausible Signal — Intermittent, No Communications - Intermittent, Electrical Fault in Circuit - Intermittent, Adresse, Address,  Betriebsnummer, WS Code, Rollbacks, Freeze Frame, Fault Status, Coding, Readiness, Klimaanlage, Cent. Elect, Gateway CAN, Inter. Monitor, Central Conv, Komfortgerát,  LenkhilfeTRW, Kombiinstrument, volkswagenowners,

COMMON VOLKSWAGEN PROBLEMS

I've owned no less than 20 cars, the bulk of which were VW vehicles. I am thus qualified to say that the most troublesome car in the Volkswagen stable without any doubt is  the VW Jetta but it is very closely followed by the Volkswagen Polo, regardless of winning  2010 World Car of the Year. 

Whether you drive an older 6n Polo or a later 9N3 Polo classic 1.6 or 2.0L Highline, or a newer Polo Vivo 1.4 Trendline, or a VW hatch 1.4TDI Highline or a VW sedan 1.5TDI Comfortline, or a VW hatch 1.2TSI Highline, or a Polo BlueMotion or a Polo GTI, or a CrossPolo, or even a Polo 6R, either manual or auto, you are bound to encounter some or all of these problems listed below over time or even perhaps in very close proximity to one another.

Since I've had my VW Polo 2.0L Highline, I've personally experienced most of them and the only reason I know that these are common problems is because I've encountered so many people with similar problems. They go as far as to say the VW Polo is a thoroughly unreliable car, adding that it's poorly built and that they should have stuck to Japanese cars. Some complain about the high repair bills they had to foot for problems that shouldn't be haunting fairly new cars,  let alone the atrocious VW customer service they experienced. Their final words - "Stay away from Volkswagen".  "I'll never buy Volkswagen again!"

Soon after I purchased  my VW polo 2.0L highline I noticed an above normal level of cabin noise. The conclusion I came to, was that the door rubbers doesn't seal very well allowing type road noise to enter. This was even confirmed by water droplets falling onto the door panel armrest and on me when it rains. In fact when I open the back doors and look at the B-post and front door rubbers seals, I can see a air gap of about 5mm between the B-post and the rubbers door seals. I would agree that the Polo isn't  built very well. 

At another time, I noticed a humming sound emitting from its gearbox when accelerating.  Convinced that it wasn't there before, or if it was, it was hardly noticeable, I took the Polo to a VW service centre, only to be told, "There is no problem with the gearbox, that sound is perfectly normal for all Polos."  Ya right! Like its normal for a person to have 4 ears.

A friend who owns a 2011 Polo Vivo 1.4 Trendline also noticed the interior cabin noise was getting quite annoying when driving at speeds above 100 km per hour. As a result he had both front wheel bearing replaced thinking that may be the problem but it didn't make any difference. The VW service centre says it has much to do with wheel balancing and alignment.

Something else I'm quite unhappy about is that the interior fabric has  separated from the roof lining of my 2007 Polo Highline  and hanging as if filled with water. However I'm not as pissed about it as my neighbour is, who ownes a 2011 VW Polo Vivo 1.4 Trendline. He says it's totally unbelieveble that a five year old car should be falling apart whereas as his 20 year old Mercedez Benz's fabric ceiling still looks new, like the day he bought the car.

The airbag malfunction light seems to be another VW problem on an epidemic scale. Once its on, it cannot be turned off, not even by experienced auto shops. Replacement of the airbag is the only way that light is going to turn off and stay off. This was a problem that originated with the 2006 VW jetta when nearing 160,000 kilometers.  Somehow this problem found its way into other VW's especially the Polos.

Another Jetta problem that seem to have infected VW Polo, is Ignition Coil failure which tend to  appear around 120,000 kilometers. Its a good idea to keep one or two spare coils in your repair kit because they die when you least expect it.  When they do, your car shakes as if its a washing machine in spin dry mode. I've also had one or two of my radiator fan lades snap off and when it engaged shook my entire car as if I small tree in a blizzard. After the initial fright when this happens is the thought of cost immediately springs to mind.  So some reason or the other my radiator fan just disintegrated.

The Check Engine light and the EPC light turning on, are classic VW Polo problem that just waits for an opportunity to present itself. This often occurs when your decelerate, or yielding or driving slowly or when you start it first thing in the morning. Its perfectly normal or the EPC light to come on during a 3 sec self test when the ignition is turned on but should turn off when the vehicle starts. If it doesn't, your in or a very long day. 

EPC problems sometimes evokes limp mode which I found can be quite dangerous even life threatening because I've experienced limp mode with a 30 ton road-train just meters from my rear bumper, with just fractions of a second to get out of its way. I've experience EPC problems on the freeway on-ramp in peak hour traffic. I've experience EPC problems on a lonely stretch of road in the dark of the night. I've experience EPC problems to the point that I didn't want t drive my Polo anymore and even contemplated selling it.

Wiring harness problems especially on the doors and the alarm system and the DSG gearbox. The headlight connectors tend to melt from the heat of the lights and contact becomes intermittent to the point that whilst driving they go on and off.

Leaking coolant from under the water pump or from the black metal hose that runs along two side of the engine. Either the water pump needs to be replaced or the corroded pipe needs to be replaced. 

VW LOGIN CODES

VW LOGIN CODES 

The "login" codes listed below work on many of the following Volkswagen vehicles listed in alphabetically. In order to use them you need a scan tool with the appropriate data connector plugged into your car's DLC connector.  VCDS software and its dual-K+CAN cable is probably your best option but is fairly expensive compared to the other ranges of DIY scan tools.  NB! Use these codes below at your own risk. If you don't have the necessary knowledge or expertise to make adaptation changes to your car's internal electronic module then it's best to leave them alone and refer these changes or logins to an automotive  professional, or at least someone knowledgeable about OBDII Diagnostic Trouble codes (DTC), vehicle  modules, intelligent sensors, the binary system, electronics and data link protocol transmission. These are extremely helpful if you've bee having one heck of a time trying to "login" to your instrument cluster to adapt some keys. Used incorrectly could turn your ECU into a brick so practice caution.

Dual-K & CAN Ross-Tech VCDS kit

Volkswagen:- (VW) Caddy (9K chassis) 1996 - 2003 and newer
Volkswagen:- (VW) Caddy (2K chassis) 2004 and newer
Volkswagen:- (VW) Corrado  and newer
Volkswagen:- (VW) Crafter (2E chassis) 2006 and newer
Volkswagen:- (VW) Eos (1F chassis) 2006 and newer
Volkswagen:- (VW) Fox/Spacefox/Sportvan/Suran (5Z chassis) 2005 and newer
Volkswagen:- (VW) Gol/Parati/Saveiro (5X chassis) 2000 and newer
Volkswagen:- (VW) Golf/Jetta II (19E chassis) 1983 - 1992
Volkswagen:- (VW) Golf/Jetta/Vento/Cabriolet III (1H chassis) 1992 - 1998 and newer
Volkswagen:- (VW) Golf Cabriolet IV (1E chassis) 1999 - 2002
Volkswagen:- (VW) Golf/Jetta/Bora IV (1J/9M chassis) 1998 - 2006
Volkswagen:- (VW) Golf/Jetta/Bora V (1K/5M chassis) 2004 and newer
Volkswagen:- (VW) Golf/GTI/Jetta (1K/5K chassis) 2010 and newer
Volkswagen:- (VW) Golf Variant/Wagon (1K chassis) 2007 and newer
Volkswagen:- (VW) Golf Plus (5M chassis) 2005 and newer
Volkswagen:- (VW) Golf Mk.6 (5K chassis) 2009 and newer
Volkswagen:- (VW) LT (2D chassis) 1996 and newer
Volkswagen:- (VW) Lupo (6E/6X chassis) 1999 and newer
Volkswagen:- (VW) New Beetle/Cabriolet (1C/1Y/9C chassis) 1999 and newer
Volkswagen:- (VW) Passat (31/3A chassis) 1988 - 1994 and newer
Volkswagen:- (VW) Passat (3B chassis) 1997 - 2005 and newer
Volkswagen:- (VW) Passat (3C chassis) 2006 and newer
Volkswagen:- (VW) Passat CC (35/3C chassis) 2008 and newer
Volkswagen:- (VW) Phaeton (3D chassis) 2002 and newer "facelift",  2007 - 2008)  
Volkswagen:- (VW) Polo (6N/6N2 chassis) 1994 - 2002 and newer 
Volkswagen:- (VW) Polo (9N chassis) 2002 -2010
Volkswagen:- (VW) Scirocco (13 chassis) 2008 - 2009 and newer 
Volkswagen:- (VW) Sharan (7M chassis) 1995 and newer
Volkswagen:- (VW) Tiguan (5N chassis) 2008 and newer
Volkswagen:- (VW) Touareg (7L chassis) 2003 and newer
Volkswagen:- (VW) Touareg (7L6 chassis) ( 2007 and newer
Volkswagen:- (VW) Touran (1T chassis) 2003 and newer
Volkswagen:- (VW) Transporter (70 chassis) 1991 - 1996
Volkswagen:- (VW) Transporter (7D chassis) 1997 - 2003
Volkswagen:- (VW) Transporter (7H/7J chassis) 2003 and newer


ENGINE
TDI Engine adaptation login = 12233 ( 4 cylinder MSA12 and newer)
EDC17 Security Access code =  12233  
EDC15/16 Fuel cooling Activation code =  10000 
EDC15/16 Fuel cooling De- activation code =  10001
Delete FMA Learning map  = 10008 
Switched EGR off  for next driving cycle = 10011 
DPF emergency regeneration V6 = 10016 
DPF emergency regeneration 4 Cyl  = 21295
Legal top speed limiter disable (AP07) = 28575
Teach differential pressure transmitter = 30605 

UDS Short Trip password = 27971
ME7 ECU Login Codes =  07825
ME7 ECU Login Codes = 01283
ME7 ECU Login Codes = 11500 Default coding
ME7 ECU Login Codes = 11223
ME7 ECU Login Codes = 11463
ME7 ECU Login Codes = 11501
ME7 ECU Login Codes = 12233
ME7 ECU Login Codes = 33162
Other  ECUs = 26262
Golf 1,6  FSI  = 10011 
Login codes for engine type AEL = 22158
Common Rail - disable top speed limiter = 10111
01283 Cruise Activation "older" vehicles
Activate ACC = 10002
Diesel particulate filter Adaptation  = 10016
Cruise Control Activation  = 11463  
Diesel particulate filter Adaptation = 21295
Special Customer Services login = 45678

ABS

Adaptation access  MK60 = 00212
Adaptation access  NDBW = 01025
Adaptation access  DBW = 04097
Adaptation access  SPECIAL A6 = 09399
Adaptation access  FWD = 13204
Adaptation access AWD = 13504
Adaptation access  AWD ESP = 18446
Adaptation access  MK60 = 19469
Adaptation access  FWD ESP = 23049
Adaptation access  General = 27861
Adaptation access to basic settings = 40168

AIRBAG

Airbag Adaptation Enabling login = 20324

INSTRUMENT

Instrument Cluster Adaptation Login = 13861

CENTRAL ELECTRONICS

Central Electronics Adaptation Enabling login = 21343
Activate Cruise Control Adaptation Login = 11463
De-activate Cruise Control Adaptation Login = 16167
Activate Cruise Control Adaptation = 13647  
NB! The  Cruise Control System  activation  Drive-by-Wire throttle systems will vary for different engine types.

STEERING

Steering Angle Sensor Adaptation Login = 40168

SUSPENSION 

General Login = 31564
Transport Adaptation Activation = 10273
Transport Adaptation de-activation = 41172

 

GENERIC AUTOMOTIVE PROTOCOLS

GENERIC AUTOMOTIVE PROTOCOLS

To date I've evaluated several VW, AUDI, SKODA and SEAT scan tools and discovered that there are many, many readers who have no idea what generic automotive protocols are or what a automotive scan tool does. The following is an explanation of automotive protocols, but if you like, you may download the PDF document that identifies which protocol / protocols are specific to your vehicle's make and model. To make things simple, if your car was manufactured after 2008 then your vehicle soley uses the  CAN protocol, whereas if it was manufactured prior to Y2K then it's very likely that it soley uses the ISO 9141 protocol, but there are exceptions. Cars manufactured between Y2k and 2007 inclusive, uses one, two or three of the ISO diagnostic protocols.

ISO stands for 'International Organization for Standardization' and is a Worldwide Federation to which  most national standards bodies situated in most countries are affiliated to, as members. Member bodies interested in a specific subject, automotive or electrical or otherwise, for which a technical committee has been established, has the right to be represented on this committee. Any draft International Standards adopted by these technical committees are then circulated to all member bodies and publication of the impending International Standard requires approval by a 75 % member majority vote before it can be accepted as cast in stone. The numbers 9141 / 1430 / 15765 are just numerical numbers allocated to standard when approved and gives you some idea as to how many standards they already approved.  ISO 9141 has been amended and is now known as ISO 9141-2.

The various colour lines depict the various bus systems. In the drawing only three modules for each bus system is shown but there could me more than 10 modules per system hence the open ended arrows. As can be seen, the Powertrain bus, the Diagnostic bus, the Infotainment bus, the Lin Bus, the Instrument panel bus and the Convenience bus are all disparate bus systems that converge at the Gateway module which is responsible or protocol translation between the various bus systems.

Anyway,  VAG vehicles predominantly use either ISO 9141-2 ("CARB"), or ISO 1430 ("KWP-2000") [Keyword Protocol 2000]  or the  ISO-15765 ("CAN") [Controller Area Network] protocol and these are the languages of OBDII (On-board Diagnostic 2) systems.   Some VWs support all three protocols and the scan tool normally used the protocol best suited for communication subject to the mission criticality and speed of the individual networks. There are other protocols in use by different car manufacturers like, LIN (Local Interconnect Network) Bus, and FlexRay, Byteflight,  and MOST (Media Oriented Systems Transport) etc... but these are not the only bus protocols used in electronics.

For example HTTP (Hyper Text Transfer Protocol),  SSL (Secure Socket Layer), TCP/IP (Transmission Control Protocol Internet Protocol) are protocol that come to mind that are used for internet communication. Then there is the WI-FI protocol for cell phone or laptop  to router communication, then there is  Bluetooth for cell phone to cell phone communication or computer to printer communication to mention but a few.

A protocol is essentially a set of rules that determines the interchange of digital information between on-board emission-related Electronic Control Units (ECUs) or two bus enabled electronic devices. Restated, how the electronic modules in your car communicate with one another and how  they communicates with a scan tool in order to display, read and clears DTC's. DTC stands for Diagnostic Trouble Codes. You may download this PDF of generic trouble codes specific to VW, Audi SEAT and SKODA vehicles. A scan tool can exchange digital information with any of many electronic modules to establish the correct module coding based on installed equipment. A basic set of modules are

Address 01: Engine   - Engine Control Module (ECU)

Address 02: Auto Trans  Transmission Control Module (TCU)

Address 03: ABS Brakes  - Assisted Braking System Module (ABS)

Address 08: Auto HVAC  - Heating, Ventilation and Air Conditioning

Address 09: Cent. Elect.  - Central Electronics Control Module

Address 15: Airbags  -  Supplemental Restraint System (SRS)

Address 17: Instruments  - Dashboard cluster

Address 19: CAN Gateway - On-Board Power supply

Address 25: Immobilizer - Immobilizer Control Module

Address 44: Steering Assist - Power steering Module

Address 45: Inter. Monitor - Interior Control Module

Address 46: Central Conv.  - Central Convenience Control Module

Address 56: Radio - Radio Control Module

Getting back to the rules, a protocol is commonly called a hand shake. It takes to parties to commit to communication. Its something like when someone comes to knock at your door, and when you hear the knock , you go answer the door. The person at the door greets and you return the greeting because it is protocol to do so. The visitor asks if this is number '303 steering module street' and you say yes. He then say he represents the electricity department and needs to take a reading of your electricity meter, you agree for him to enter. He then capture the information in his palm top, thanks you for you cooperation and you let him out and closed the door behind him. 

Likewise the scan tool (someone at the door) sends a signal (knock on the door) to the engine control module or the steering control module, or the gateway modules. The relevant module (you) receives the signal and decodes it, then determines (the nature of business) that the scan tool requests access to its internal non-volatile memory. Because the request signal had the appropriate greeting, the relevant control module reciprocates and allows its contents to be read. Thereafter the scan tool transmits an  exit signal and the control module releases or shuts down communication.  That basically describes a successful yet very simplified digital information interchange between scan tool and control module. However, all this is done in  naughts and ones, the bits and bytes of binary code and is a lot more intricate than described but the objective was just to give you a general idea of function of a  protocol. 

CAN-bus is used for the Drivetrain Network
CAN-bus is used for the Instrument Cluster/Suspension Network 
CAN-bus is also used for the Convenience Network
CAN-bus or LIN or MOST is used for the Infotainment Network
CAN-bus is also used for the Diagnostic Network