VW electrical issues

VW Electrial issues

As we all know, Volkswagen, Audi, Seat and Skoda have several mechanical and electronic components in common, among which are their wiring looms with their huge variety of connectors. These connectors range from as few as 1 or 2 contacts per plug, to as many as 16, however the ECU and TCU edge connectors can range anything from for 32 to 68 pins,  up to 80 pins and even beyond. 

AUDI, VW, Skoda and Seat 2 pin connectors P/N535972721 - P/N1J0973772

Most modern cars have numerous control modules, for example the ECM (engine Control Module), the TCM (transmission Control Module), ABS Module (Anti-lock Braking System), Air bag Module, Convenience Module, Steering Control Module, Radio Module, Central  Electronics Module, Instrument module, CAN Gateway Module to mention just a few. Bearing in mind some cars have as many as 40 modules or more on board. 

TCU, ECU and Air bag plugs showing the multiple pin contacts.

Some of these modules control the sound system, the telephone system, the satellite navigation system, xenon ballast module, fan control module, suspension height control system, traction control system among so many others. Each of these modules and systems have numerous connector terminals / pins, some for its primary power, some for standby power, some for data communications, some for sensor inputs, some for actuator output, some for future expansion, some to accommodate different models  and probably some just for show. Each of these modules can have just a few contact terminals / pins whereas others can have close to 100 contact pins.

Molex ECU and TCU interface connectors that are normally
soldered onto the Printed Circuit Boards

When this glut of electrical contact terminals / pins / connectors are compared to those  of a pre-1994 vehicles, you shouldn't be surprised to see that they increased by at least a 100 fold. Meaning if your car of the 90's had as few as 200 electrical connections throughout the entire car, then its 2017 version would have 2000 electrical connections bumper to bumper. This is just a poor estimate for the sake of clarity but in reality their are way more connections. Pessimistically speaking that implies there are an extra 1800 connections that could go awry at any time, especially whilst driving in peak hour traffic or on a deserted road. Some of these 1800 connections include those for the EPC circuit, the throttle body, the check engine light, the crank sensor etc, and some many others that can be the cause that your car breaks down at the road side, leaving you stranded when you need the car most.

Female terminals seem to be the most troublesome of all connectors.

Since all cars are subject a certain amount of vibration that permeates throughout the body of the car, wiring looms and their connections are vibrating along with the engine, or bouncing and shaking along due to poor road surfaces. The car's body also flexes as it drives and the wiring harness flexes right along with it. Most of the VW plastic plugs and connectors have a locking system to keep them together, to prevent them from becoming adrift  whilst driving. But if there is excessive movement in the plug itself that causes contact friction, these contacts are not going to survive very long. The funny thing is, that we see this happening on a daily basis. Then there is chaffing of the loom against the car's body in places where goes through the firewall and the A and post.

The DLC 16 pin connector and a 12 pin connector with their crimp-on terminal pins

Most mornings on my way to work I see at least three rollback tow trucks either in the process of loading a VW or I see the rollback driving in the opposite direction of my travel or I end up over-taking  a rollback with a VW on its back.

So by just looking at the female terminal pins of all the images above, one can clearly see that all of them sport a tweezer like female tension receptacle that squeezes the male pin when it is inserted. Each of these female contact terminals have two little wings that secure them inside its plastic plug but when the terminal  goes intermittent contact it need to be replaced with one of the VW replacement wire kits displayed above.  

VW wiring harness connector terminal removal tool.

The "VW Wiring Harness Connector Terminal Removal Tool" below is used for this purpose, ie to release the terminal pin from its plug. Alternatively you can make your own tool with a paper clip. Straighten the paper clip then hammer both ends flat, then bent it in half to form a staple, so that the two flats are parallel to one another. The hammered flat edges can then be inserted on either side of the terminal pin  so as to push the terminal's wings back onto itself, making it easy to pullout.  Look at the image below. VW 2 pin coolant plug seems to be a favourite that goes wonky and needs replacement. Audi throttle body connector is another. VW, Audi 6 pin accelerator pedal plug is another troublesome connector. But that's best left for another post.

Cross section of terminal plug thats been cut open, see how the two wings in 
the top image is pushed flat by the harness connector tool in the lower image.