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David
David, VW Master Technician
Category: VW
Satisfied Customers: 2361
Experience:  VW Master Technician Certified for 9 years, ASE Master Technician Certified
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Volkswagen Jetta GL Just purchased a 97 Jetta GL 2.0 with

Customer Question

Just purchased a 97 Jetta GL 2.0 with 80K–connected a Code Reader (OBDII compatible) but unable to establish any communication-everything else works as normal-

Is there a main fuse which protects the diagnostic link
(the code reader is functioning correctly)

Thanks for any direction
Submitted: 3 years ago.
Category: VW
Expert:  vwtech0405 replied 3 years ago.
Welcome to Just Answer!!!

Does the vehicle has a aftermarket radio installed ?
Customer: replied 3 years ago.
Yes a JVC
Customer: replied 3 years ago.
yes a JVC
Expert:  vwtech0405 replied 3 years ago.
Ok that's why the scan tool will not communicate because it was wired incorrectly you will need to remove it and unplug it comely from the stock factory harness then you will be able to communicate with it . I hope this helps

Please don't forget to click accept for my time and knowledge thank you
Customer: replied 3 years ago.
I will try your suggestion and advise on the outcome
thanks
Expert:  vwtech0405 replied 3 years ago.
No problem please don't forget to click accept for my time
And knowledge thanks
Customer: replied 3 years ago.
I removed the radio, and disconnected the wiring harness-but still unable to establish any communication-

What should I try next?

Thanks
Customer: replied 3 years ago.

I don’t have a frame of reference – can you send me schematic of what the wires should look like behind the radio so I have something to compare
Expert:  vwtech0405 replied 3 years ago.
Did you also unplug the factory harness from the after market one ?
Customer: replied 3 years ago.
I only see one harness and that is plugged into the rear of the radio -

Can you send me a photo or a schematic of what the (factory wiring harness) should look like behind the radio - It would be helpful to have a visual comparison

Thanks for your help
Expert:  vwtech0405 replied 3 years ago.
I don't have any pictures that will help . There should be a harness from the radio to another factory harness if it was wired right
Customer: replied 3 years ago.

I don’t have any knowledge of the original wiring harness- It would assist me greatly if you could please refer to the shop Manual and detail the colors of the wires that are leading to the factory wiring harness- then utilizing this comparison I can establish a basis for us to move forward-

Thanks for your help
Expert:  vwtech0405 replied 3 years ago.
provide me the vin # XXXXX i can look up the wiring diagram
Customer: replied 3 years ago.

VIN # XXXXX
Expert:  vwtech0405 replied 3 years ago.
Ok I will post the results tomorrow from the shop when I get access to my repair manual
Customer: replied 3 years ago.
Were you able to procure the wiring info from your repair manual
Thanks
Expert:  vwtech0405 replied 3 years ago.
Is the connector you have a 8 pin connector on the factory harness??
Customer: replied 3 years ago.
I don't have a factory harness - there are 13 wires in the Radio Cavity

11 of the wires are connected to the JVC radio - the other 2 wires are “Not Connected” to anything

I've included the colors of the wires and their size to help with your identification - the thickness of the wires are all 1.0 unless noted

BROWN (1.5)
BROWN/WHITE "Not Connected"
BROWN/RED
RED/WHITE (1.5)
GREY/BLUE "Not Connected"
BLUE/GREEN
BROWN/RED
BROWN/BLUE

BLACK
RED/WHITE
BROWN/WHITE
BLUE/GREEN
BROWN/RED

Thanks for your help
Expert:  vwtech0405 replied 3 years ago.
You have to have a factory harness/wiring that plugs into the aftermarket harness or taped into a factory harness , this is how the radio gets its power source
Customer: replied 3 years ago.

JVC provides a wiring harness which plugs into the back of their Radio – the wires coming from the JVC harness are connected with (simple PIG twisted) connector to the wires in the dash-



To reiterate from above, if you compare the colors of the wires above against the schematic in your Service Manual you should interpret a correlation-



If you analyze the color of the wires above you should see that the radio power is derived from RED/WHITE (1.5) which should correspond to the schematic in your service manual – AND I know that the BROWN (1.5) is GROUND


I have obtained the schematic for the JVC radio, and it confirms that power to the radio definitely comes from the RED/WHITE (1.5) - If you want to fax me a schematic from your Service Manual I could match the radio wires for you



– 11 of the 13 wires have a radio function (like front left treble, front left bass, front Right treble , front right bass etc.) –


the 2 wires that are a concern are the BROWN/WHITE "Not Connected" and GREY/BLUE "Not Connected" – I’m suggesting that possibly the problem with the OBDII Diagnostics Connector may be with these two wires but I don’t have a schematic to make a determination and I don’t want to start melting wires by experimenting haha .

Have a good day and thanks for your help
Expert:  vwtech0405 replied 3 years ago.
Here is the wiring diagram .

graphic

graphic
Customer: replied 3 years ago.
The 1st Image is perfect, the 2nd image doesn't expand to the same extent and the detail is difficult to read-

I'm not sure what control you have over the image quality, but is it possible to resize the 2nd image to match the size of the 1st image

Thanks
Expert:  vwtech0405 replied 3 years ago.
Sorry but this is all i have the other wiring diagram came out small on my side also
Customer: replied 3 years ago.
Thanks, XXXXX XXXXX able to enlarge enough to get some detail

I went through the schematic and it shows my 13 wires.

The JVC radio is only using 11 wires - 2 wires aren’t utilized-

I note that there is a (1.5 ro/ws) used by the radio, the DLC, cigarette lighter (which is working fine) and Luggage Compartment Release Switch (which is also working fine)-

I haven't metered T16\4 but should it show 12 V? -- since everything else connected to that power source is functioning I believe it's getting power, just not a signal

Which would be the 2 wires that would still allow the radio to function but could effect the signal to the Data Link Connector (DLC) – and what is the procedure you normally follow with the extra wires when you’re replacing the original VW radio with an after market product

Thanks
Expert:  David replied 3 years ago.
locate the gray/blue wire at terminal 6 of the 8 pin conector. Cut this wire. This is the K-wire or communications wire to the radio. This should allow you to communicate with the vehicle. Please accept VWtech0405 diagram answer.
Customer: replied 3 years ago.
Hi David - To reiterate from an earlier post: "the factory pin connector has been cut out and removed" – all I have to work with are 13 loose wires of which 11 are connected to the JVC radio

-- the gr/bl (gray/blue) wire you referenced (as pictured on the schematic @ T8/6) has already been cut and is just sitting there unused- I haven't yet tested T16\4 on the DLC, should it show 12 V?

-- Also can you please ask VWtech0405 to forward the schematic of the DLC (Data Link Connector) as it would be helpful to see where these wires are connected-

Hey David, thanks for assisting VWtech0405 .. is that a Road King or a Gold Wing?)

cheers
Expert:  David replied 3 years ago.

OK here is a copy of the diagram for the DLC. Terminal 16 should have power. Now if you have power and still no communication, then it is highly likely that a control unit may be bad. You would need to disconnect all control units, Engine, Airbag, ABS, Transmission etc. Then connect one at a time to see which one is not allowing communication. Since all control units share the K-wire if one shorts out, you have no communication with anything. Also locate the K-wire on the DLC and using a volt meter see if you do not have a short to positive. Check for voltage at that terminal. Do not use a light tester for any electrical tests on this car, can cause a feedback issue and damage control units. Let us know what you find for further.

 

Click here for diagram

 

The bike in the picture is a Harley Electra Guide. Similar to the Road King but fully dressed. Take it pretty much every were I go. Don't drive a car too much.

Customer: replied 3 years ago.
Thanks for the diagram- “… Now if you have power and still no communication, then it is highly likely that a control unit may be bad. You would need to disconnect all control units, Engine, Airbag, ABS, Transmission etc….
......
Question: If a control unit was bad, would the Check Engine Light come on to indicate a problem?
......
Should I be concerned with (0.5 br/ro T8/1) which seems to have some involvement with J284 (Alarm system Control Module)?
......
Also I’m puzzled over the 2nd wire which is cut and just laying there, it is a (1.0) (br/ws Brown/White), yet according to the Schematic, the (br/ws Brown/White) is an internal speaker wire (Connecting R23 speaker) and I should not even be able to see it connected to the Radio---- perhaps my wire color is wrong? ... in your experience WHAT OTHER WIRE besides the gr/bl (K wire) could be cut and yet still permit the radio to function correctly?

......thanks for your help
Customer: replied 3 years ago.
to make it a little clearer "if you were installing a new radio, which 2 wires would you cut?"
thanks
Expert:  David replied 3 years ago.
To eliminate the radio connections as a possible interference with the scanner you only need to make sure the K-wire is cut out of the radio. If this is the case, then you need to start looking at the DLC, make sure there is power, if so then start unplugging control units. Something is causing the communication to be shut down. This is assuming that you have already checked the new scanner on another vehicle to make sure it works ok.
Customer: replied 3 years ago.
Checked the scanner and it works fine in the other vehicles

I’m puzzled over the 2nd wire which is cut and just laying there, it is a (1.0) (br/ws Brown/White), yet according to the Schematic, the (br/ws Brown/White) is an internal speaker wire (Connecting R23 speaker) and it doesn't connect directly to the Radio

--- in your experience WHAT OTHER WIRE besides the gr/bl (K wire) could be cut and yet still permit the radio to function correctly?

thanks for your help
Expert:  David replied 3 years ago.

This is the ground wire for the speaker, they may have joined another ground some were else, this will not effect the scanner. The only wire that will affect the communication is the K wire. The other item if there is not power at the DLC terminal 16. Something is killing the communication on the K-wire. Since it is a digital signal a short to ground or short to positive will kill communication. Most of the time when a control unit fails it shorts it to ground.

 

I recommend you try this really quick and see if this helps. You can try rebooting all the control units. Sometimes this may work. Disconnect the battery negative first then positive with both cables disconnected touch them together. This is called a capacitor discharge. Once you have done this reconnect the cable, positive first then negative. Make sure this done with the key off and out of the car. Be ready for the alarm to activate as soon as you connect the second cable. Once this happens just use the key and lock and unlock the car. You can use the remote if you have one.

Customer: replied 3 years ago.
Sorry but I've had a lot on the go at this end and I'm not going to have an opportunity to try this out until after Christmas - I'll be back in touch then

Thanks and Merry Christmas

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