Dealer says I need a new ECU?!?!

So im somewhat new to these forums, and have done some research and found out there are common problems with cold starts and glow plugs etc. I will be doing some of my own tests thanks to your helpful posts.

Heres the scoop. Bought my 09 TDI in September 2014. Had a check engine light, and the code was PO684. Glow Plug Control Module to PCM Communication Circuit Range/Performance

So no problem. The car always started fine. When it got colder, it would have to crank a little longer, but it would start. Now that its very VERY cold out, its extremely hard to start, and takes a long time of cranking, waiting, cranking, waiting, etc.

Dealer recommended i replace the Control Module. No problem. All it was was a glorified relay, that was placed under the battery, so I did it. Still had an issue with it and took it to the dealer, and he fixed it and said it just wasnt plugged in completely all the way. (It was very cold outside and snowing and a tight spot so i did all i could to hear it click in, in which i never heard the click in)

Problem persisted though, so i paid VW 3 hours diag time and they checked all the wiring and ground points and saw all of that was good. They said it was probably a ECM problem and that it would be $2100 to replace. But with a discount they could do it for $1600.

So again, the car starts in the warmer weather no problem. When its cold, it takes alot of extra time. So any input on what to do next? Pretty pissed about this. Ill have to take the corvette out of the garage and drive it until it gets a little warmer out. UGH!!

So, how cold is it when you are having starting issues? Everything is relative to what you think is "cold". It's currently only -18F here.
Get it to someone who will diagnosis it properly, it could be many things, some of which are pretty simple. I doubt it needs a new ECU.
If you are parking outside at home, get a coolant heater installed even if you get the problem sorted out. It's easier on the car and the driver.

Jettawreck is right, get a coolant heater, while that may not fix your problem, they can be had for far less than $1600 dollars. I installed a Frost Heater last October and Monday morning it was -14F here and after having it plugged in for 4 hours on a timer, the glow plug cycle lasted about 3 seconds and it started like it was a summer day. That will give you time to sort out the issue when it's a little warmer.

OP: do you have any DTCs stored right now?

I had a 2009 towed in this week with a no start complaint. Battery had been cranked flat, tried jumping, still would not start (it was about 6F that morning).

I pushed it in the shop, put the battery on a charger, and scanned it for DTCs and got the same P0684 that you had. I checked the visual integrity of the connector at the glow control unit, didn't see anything amiss, so I went ahead and ordered a new one. Installed that, and my P0684 went away, only now I have a hard DTC P0670 glow plug module 1, glow plug circuit. And it is still very difficult to impossible to start in the cold.

I am probably going to dig into it further today, but as of right now I could not find anything wrong with any of the fuses in the underhood fuse plate, including the F27 big 50A job that should be the circuit for the actual glow plug load themselves (the BIG 6mm wire going into the control unit).

I'll let you know what I find, but I cannot recall ever coming across this particular P0670 DTC before. Usually it is a specific glow plug call out, this seems to be a more ambiguous DTC and searches here have had people ask about it but get no resolution.

I do know the fuse plate is melted, but it is in the usual spot, on the rear most smaller 30A fuse, and that problem *usually* manifests itself as some other issue as wonky headlights, etc. Many of these cars were under recall for this, and I have a new one of those on the way just in case (they are easy to swap).

Oilhammer comes thru with some excellent pertinent info.

Ok, this one was fixed with a new underhood fuse holder plate. Some bad connection somewhere inside.

Also, be sure that glow controller is properly seated all the way down on the connector. Mine was not the first go around. It actually holds air inside of the little "skirt" around the unit itself, so you have to press really hard and continually to get it all the way seated until the clip snaps into place.

The fuse holder is pretty easy to replace. Disconnect the battery, remove the fuse box cover, remove the wires from the bus bar (the 'SA' fuses) in front of the fuse box (bunch of nuts), then loosen the one Torx captive screw in the middle and the whole box will lift right up and out.

You'll need to transfer over all your fuses, so do them one at a time to make sure you don't misplace any, and check each one carefully for any burning or melting spots, replace with NEW NON-CHINESE fuses if necessary, then place the new holder over the box, and carefully start that Torx screw and run it down until it seats. Just snug it, don't overtighten it!

Then put the fuse link wires back on the bus bar at the front, again checking for anything that is dirty, corroded, or burnt, put the cover back on, reconnect the battery, then reset/clear any DTCs, windows, clock, etc.

i will be doing this ASAP oilhammer..thanks for the info!!! Do you have the old part with a picture to pinpoint if there was any physical damage to look for?

No, I don't have it (well, it is in the dumpster somewhere, and it is 5F out, LOL).

I didn't really see anything besides the [common] burnt/melted fuse position at the rearmost point, towards the windshield.

But like I said, that usually causes other issues.

Your local dealer probably stocks the fusebox. Just have your VIN ready.

oilhammer said:

Ok, this one was fixed with a new underhood fuse holder plate. Some bad connection somewhere inside.

Click to expand...

If it turns out this is a same problem with OP car , imagine he pay $2000 for ECU swap and has same problem.
I can not understand people who works in dealer , specially this is a known problem with this fuse box.