VW / Audi / Seat / Skoda Aftermarket Radio Trouble Effect Launch X431

VW / Audi / Seat / Skoda Aftermarket Radio problem

Affects Diagnostic Tools including Launch X-431 , Infinite, Tool & Crecorder

VW / Audi / Seat / Skoda Aftermarket Radio Trouble Effect Launch X431

The background

Many VW / Audi/Seat/Skoda (VAG) radios are ‘diagnostic capable’ – meaning that the dealerships can communicate with the radio to, for example, set whether a CD changer is present,or to test the speaker outputs. This connection is provided by a wire between the radio and the diagnostic connector on the car (known as the K-line)


If you want to get more Launch X431 test case check here:How to Use Launch X431


The problem

When fitting an aftermarket radio to a VAG car, many owners use an off-the-shelf wiring harness to connect between the car and radio wiring.

Certain wiring harnesses do not deal with the K-Line wire correctly, and short it to the 12V supply from the battery. Whilst this doesn’t affect the car at all, it can badly damage diagnostic equipment when it attempts to connect to the car

Diagnostic tools ground the K-Line to initialise communications, but if a hard 12V is present on the

K-Line, this can’t be grounded, and will damage the K-Line driver on the diagnostic tool


The solution

Some modern VAG specific diagnostic interfaces contain protection against this problem, and will simply not connect to such a car. Care should however be taken when connecting any tool to a VAG car with an aftermarket radio present. Many garages still refuse to COffi1ect to such a car if an aftermarket radio is present as replacing a garage-based diagnostic tool is very expensive


Testing for the problem

It is possible to test for the problem

If the car is a pre-1996, then it is most likely to be fine. The K-Line did not go to the radio before then.

On a post-1996 car: measure the voltage between pins 4 and 7 on the diagnostic connector (Iayout shown below)

If the voltage is below 9 V then it is fine

If the voltage is over 9 V then more testing is required. A lk Ohm resistor should be temporarily connected between pins 4 and 7, and the voltage should again be measured (in parallel to the resistor)

If the voltage is now down to about 1 V the car is fine. If it is still at around 12V then the Aftermarket

Radio Problem is present (the resistor will also get hot if this is the case)

If diagnostic equipment is damaged

‘For Launch ‘X-431 Infinite,and ‘Tool’ diagnostic scanner, if the K-Line is shorted to 12 volts then the tools circuitry is protected by a fuse soldered to the Smart box circuit board. The tool will need to be returned to Launch for the repair to be done (Note: this repair is not covered by warranty)

For Launch CRecorder, if the K-Line is shorted to 12 volts then the tool is permanently damaged and considered unrepairable.

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