2005.5 Communication failures?

KenG

New member
Joined
Aug 5, 2020
Location
ohio
TDI
2005.5
Auto tech with extensive knowledge in subarus, still learning VW stuff.

Recently picked up a 2005.5 BRM Jetta. Began with a no crank/no start. Would come and go as it pleased. Ended up hooking the starter signal wire to a 12v push button so that i can start it when i want and bypass whatever is wrong.

I dont have access to VCDS currently, waiting on my cable in the mail.

So now it starts every single time without fail. My traction control and steering wheel light (amber not red) are constant. The only code I ever pull from OBDII is a P0600, a serial communication failure.

Sometimes, after i start it, i'll have no speedometer, odometer my fuel gauge does what it wants, no AC and my trunk/fuel switches wont work.

Sometimes everything functions as normal. Speedometer works, ac is cold, fuel gauge is constant.

Ive thoroughly read about the BRM engine wiring harness issue, but have checked all of the rub spots that have been mentioned, and never found a single chaffed wire. However, PO hacked up the radio harness. Still have to sort this issue out.

Is this pointing to a bad ECU or some other module that is losing communication? Ive checked most of the grounds and even added a couple to help out the starter.

Pulling my hair out here while waiting for vcds to be able to tell me more. Any help would be greatly appreciated.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Yeah, OBD works, you need to start there... so wait for your VCDS. Otherwise, you'll just be spinning your wheels (or pulling your hair).

When you get it, start with an Auto Scan ---> Gateway Installation List. That'll quickly go to the CAN Gateway, and have it tag all the modules, list them out, and any in RED will be holding DTCs. I suspect many of them will be red on your car.

The radio wiring may be a clue, as you could have some CAN bus wires (the radio is just another module on the network as far as the Gateway is concerned) all screwed up.

Also, there is no ignition "switch" in the traditional sense on that car. It is more like a key position sensor, which feeds this information into the Steering Column module, which then shares this information with the Central Electronics, CAN Gateway, and Instruments as to where the key position is. So there are lots of steps the electrons have to take just to make the car start, and you cannot check them with a test light, because we are talking low voltage packet type signals being passed between processors at nearly the speed of light. So you for sure need to tap into the data block of these various modules.

Volkswagen is about 10-20 years ahead of Subaru in terms of technology like this, so I can understand the learning curve may seem steep for you, but rest assured they are not that complex once you know some of the basics and how to use things like VCDS. I have a friend who was a Subie tech for a long time, we laughed about them still using carburetors into the '90s, LOL.
 
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KenG

New member
Joined
Aug 5, 2020
Location
ohio
TDI
2005.5
So finally got my vcds, ran into a couple electrical issues that had to be sorted out, and this issue hadn't happened since. But it happened again this morning. Can do a autos an, but it always hangs at the abs controller. Would the abs controller also kill the speedo and odometer?

I'm actually doing about 55mph here...

 
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