Random electrical issues causing no start.

[Herc]

Dealership is running a CAN line test tomorrow, something I mentioned over a month ago, also received a heads up on checking the CAN gateway,

another thing I mentioned to them over a month ago, they can't seem to let go of it being a DME issue. Guess the CAN test will look into both.

We'll see, CAN gateway module is pretty cheap at $190.

Codes only show up when the car is having the problem, when it starts it shows no codes.

[binger]

The instrument cluster is the CAN gateway module. AKA COMBI meter / Gateway. If you look at the PDF uploaded. Check out at the CAN topology. At the top is your COMBI meter / Gateway or "instrument cluster". The blue line is your high speed CAN that runs the most important systems in your car. then it splits down to red line medium speed that runs the body modules and so on. Hope this helps you understand a little more about how things work in CAN systems.

CAN.pdf

[RFM]

On a 997/1 is the gateway still clung under the wipercover, left side in the corner, next to hinges of the front trunk lid, below a square black plastic cover fastened with screws. The seals of the covers L and R, and even more wiring protection, should be replaced/placed by a Workshop-action due water penetration in 2006/2007 i would guess. I did a lot of 997/1 with this issue.

[Herc]

Well they ran a full CAN line test, 4 hrs worth, and are saying it is the DME. They were able to get it to fail while hooked up to the tester and all

other modules checked out OK.

[binger]

Are you going to install a new stock flashed DME or new aftermarket flashed DME?

[Silver_TT]

Along the same lines as what binger is saying, if what you stated is the case I think it still could be the software flash rather than a hardware problem with the DME. I'm not saying this is definitely the case, a hardware fault would not be completely unrealistic. However, at this point I still think it would be prudent to try the stock flash just to baseline what's going on here. You need to do your best to take this back to a known configuration to get to the bottom of this seemingly random erratic behavior that the car is exhibiting before start-up. As I mentioned earlier, this takes just 5 mins with a PIWIS or with your tuner's software and a laptop. I've done this myself and it's so easy. The flash file for your car is just a few hundred K in size (less than a megabyte if I recall) or so -- tiny. It doesn't make sense to me for you to spring for a new DME $$$ until you've ruled this out and are operating in a configuration that is known/tested/etc.

Edited January 16, 2014 by Silver_TT

[Herc]

Having them flash to stock tomorrow. The CAN line test showed that as soon as the DME was hooked up the neg signal went to zero meaning the

DEM was grounding out the CAN bus. Weird thing, the tech working on the car is able to get it to fail/no start at will; starts fine then he turns it off,

key back to on for 5 min then off, key back to on and it fails, then back to off for 5 min and it will start fine. They had Porsche on the phone while

the test was running, Porsche would not send them the protocol for the test due to proprietary issues, so good thing he was able to get to fail for

the test. Although this is the exact test I mentioned over a month ago after downloading a Porsche electrical diagnostic pamphlet.

[Herc]

I didn't think it was the GIAC flash and it appears I was right. I had them re-flash to stock and it did not fix the problem so they have ordered

a new DME. Guess I am one of the very few unlucky ones with a bad DME. How often have you heard of that?

[Silver_TT]

Not very often assuming there was never any moisture in it, etc (although not impossible). I know it sounds like they already have but I would just double check to make sure all the connections and downstream wiring are good.

[Herc]

Yep, all wiring was checked and they had Porsche on the phone when they were running the CAN line test, which had them unplugging and

re-plugging just about everything, wires, relays, modules etc........ It would be interesting to find out what exactly is bad inside the DME, has

to be a bad/cold joint.

[Herc]

Looks like the problem is going to be the after market daytime running lights. Seems they are wired incorrectly

into the "15" power and are shorting out the system. When unplugged the problem went away. Weird one.

[Silver_TT]

Glad you got it sorted. Gotta be careful with after market stuff and I'm personally not a fan of it at all. As I alluded to, adding aftermarket flashes, parts, etc -- you're taking the car away from a known, heavily tested configuration. Your car is an amazing car just as-is, stock, in my opinion. Very happy you are back in business.

[binger]

Are there any other aftermarket electronics in the car. IE: alarm, radio, nav.?

I am glad you found the root cause and solved the issue! If you look back on my second post that was one of my first questions.

You just experienced how aftermarket installers that do not know what they are doing can cause really hard problems to solve. Also how much time and money did you end up putting out because of there lack of knowledge?

[NeoMatrix]

Many thanks to all that have contributed here.

 

I too have a 997.1TT, with the same/similar problems as the OP. My problem is that the car sometimes does not start on the first try (starts on 1st try only ~50% of time). The car ALWAYS starts on the second try. The car has never not started.

 

My setup is:

• DME Reflash with EVOMS 550 program,
• Aftermarket Daytime Running Lights
• Relatively new (within last year) alternator, battery, updated grounding and alternator cables.

I disconnected the Daytime Running Lights and the problem still persisted (starts on 1st try only ~50% of time).

 

I'm thinking here the best way to proceed is to re-flash the DME to the stock program? There are no other mods on the car.