2010 Jetta Intermittent No-Start, U0100 fault

My Jetta has 83,000 miles and for the past 2 months I've been experiencing an intermittent fault that is becoming more frequent. On average every second start gives me troubles now and one of these days I'll likely be left stranded.

I've taken the car to one shop recommended on here by some local members but all they did was charge me a hefty diagnostic charge only to tell me the Scangauge may be the culprit. They didn't mention anything about looking at any other potential causes. When the problem resurfaced with the SG unplugged, they told me I need to take it to the dealer...

Symptoms:

The glow plug indicator does not light - sometimes it comes on after 1 second, sometimes not at all until I've cycled the key multiple times. If I attempt to start the engine before the GP lights, the engine only cranks. There's a loss of communication between various modules and the ECU. Code U0100 is stored. "ESP Error" will display on the MFI if the GP does not light within a couple seconds.

When the car does start after this problem has presented itself, the gear position indicator fails to display and the transmission fails to shift out of park 50% of the time. That forces me to shut it down and restart.

While running the car has never had a hiccup, but starting can be an ordeal.

I've tried one independent shop and I'm hesitant to try another before better understanding this issue myself. I'm particularly hesitant to take it to the dealer. They may be the best equipped to properly diagnose it, but that's contingent on them being trustworthy and having experienced technicians. We've all had horrible experiences with dealers and I'm not keen on paying for multiple parts to be replaced until the problem goes away...

Any thoughts or recommendations?

Hopefully it's just a bad relay or loose connection.

If you don't trust the dealer, find another shop. It is much easier to diagnose the problem with the car in front of you.

Strike 1 with the first shop that was supposedly a reputable shop. They were in over their heads. Not many other options in Calgary.

U0100
ECM - Communications lost

Recommendation:
Check main power relay (code 458).

Fuses B13, B14, B21, B22, and B23 will be 0V to ground when the J317 is not ON.

If J317 socket corresponding to terminal 86 (look at relay) is 12V, check terminal 85 - resistance to ground should drop when the ignition is switched on.

If the signals are correct - replace J317 (1K0906381).

Not sure if that applies to Jettas with CAN bus. I see no mention of J317 anywhere unless I'm looking in the wrong spot.

Look in your engine compartment relay/fuse box. It's #458. Of the two in the box, it's on your right.

I'm not sure what you mean about CAN bus. It's been in use at least since the mk4 was built in 1997.

The only relay under the hood in the fuse box is code 100.

That is the relay that I'm referring to. 458 is what's in the documentation, but the code 100 relay performs the same function. Run the checks I mentioned earlier and report back.

I'll look into why you would have the 100 instead of 458. What's the production date on your chassis?

Thanks, I'll look into it. The assembly date is September 2009.

The relay under the hood is part 7M0951253A. $10 part. I need to buy a multimeter to test as mine is packed away (recently moved) :-S. I could replace this relay for less than buying a multimeter. Of course if that's not the issue then it's a waste of $10.

Jcrews, were you thinking I had a 2006 or earlier TDI? It looks as though the 2006 had the code 458 relay under the hood. I've read a bit about the ALH TDIs having issues with relay 109, which sounds similar, but no mention of such issues or a similar relay on my car in any of my research.

No. I was looking at the cjaa chart for production starting July 2009. 458 is the code in the main power relay slot.

It's a typical contact relay and is interchangeable with 100 but 100 is listed for motronic.

Do the tests as requested and you'll have some more information.

Okay, let me make sure I have this right. If the results of the tests are as you describe, that indicates the relay is good or bad?

What do you mean by "If J317 socket corresponding to terminal 86 (look at relay) is 12V, check terminal 85"? Where am I attempting to measure 12V for that part of the test?

It indicates conclusively only that there is or is not a problem other than the j317 relay itself.

Further testing on the relay itself would be needed unless you just substitute it for a known good one if the tests pass.

Check for 12V at relay terminal 86. Then check for low resistance to ground with the ignition on to terminal 85. The terminal numbers are molded into the relay cube so you can locate the correct sockets easily.

I didn't have the right tools to attempt my own diagnosis. The past few days the car gave me a lot of trouble so I took it to a dealer yesterday. After an hour they couldn't diagnose the problem. I authorized another two hours of diagnostic work. They checked various relays to no avail and want to trace wires next... *shrug*. This may get expensive quick.

Great, go figure, they're still looking into it but they're pointing at the ECM right now... It was suggested by the independent mechanic that the Scangauge may have damaged the ECM but that strikes me as unlikely.

It might be worth it to just replace j317 if you can't run the tests. Many dealership techs are frighteningly bad at everything.

Supposedly they tried that. The relay was triggering okay but not at the appropriate time.

The guy really did seem to be putting a lot of effort into it. I am being charged for 3 hours of diagnostic work but he put more into it. They did a pin-out test (?) on the ECM and said it checked out okay as far as they could tell. That's when they called to inform me they were contacting VW Tech Line. Their recommendation was to replace the ECM and relay control module (3 hours of labour). I will be out over $2500 on Thursday when the parts are in and the car repairs have been made... I requested they give me the old ECM. Apparently there may be a core refund which may mean I wouldn't get the ECM but would be out a bit less money. The service advisor wasn't sure on that one.

Hopefully this fixes the problem or else I'll be in real trouble.

Have you heard of many ECMs going bad on 2009 and later VWs? I couldn't find many reports...

The other thing to look at is J681. As you describe it, terminal 15 seems fine, though. It's easy to test by checking for power signal at fuse C2 (there are others as well) at ignition turn-on.

Are there any other faults anywhere when doing an autoscan?

J317 turns on but at the wrong time? That doesn't make much sense. I'd be looking for an underlying cause there, if there really is a problem.

Shotgunning parts is just not a good idea.

Well, by the sounds of it, they did a lot of diagnostic work. I don't know all details of what they checked. It was someone above the dealer's heads that recommended replacing the ECM and relay control module (not even sure what or where that is). You seem very knowledgable. If you were 2000 miles closer I'd gladly pay you to look at it for me. Unfortunately I've exhausted my options. I don't have the knowledge or tools to diagnose this. I've already taken it to the recommended independent shop in the city and they had no idea... The dealer put in a lot of time to figure it out but in the end had to contact VWs tech like. This was the first time they've encountered such issues. I find it strange they tested the ECM and couldn't find a problem with it yet the tech line guys suggested replacing it. That makes me nervous. If I pay over $2500 and the problem persists, I'll be quite upset.

What activates J317? My understanding is that there is a relay (not sure which to be honest) that wasn't turning on at the right time. My interpretation was that the ECM was triggering that relay. If a capacitor (assuming the ECM has any caps) were charging or discharging improperly, would that cause intermittent relay triggering?

I've authorized the work (over the phone). The service advisor seemed very confident this will fix the problem. All I can do is hope. I probably don't have any recourse if the problem persists.

Sorry to waste your time but I hope you can see I have limited options.

J317 (terminal 30 supply) is pulled down by an output amplifier in the ECM. The initial ECM power (terminal 15) is supplied through J681, which is closed by J519 (central electronics controller). Once the ECM is ready, it pulls J317's coil to ground, runs any self-calibration tests, and becomes ready to start (crank).

Hence, in this situation, I would check both power supplies for any fault conditions.

There are no significant caps to charge in the process.

As you can also see, replacing both the ECM and central electronic module will almost certainly repair the complaint, since it's most of the electrical system involved in your trouble. I hope it works out for you; keep us posted.

So the central electronics controller is what they were calling a relay control module? Perhaps I should request that they replace that ($150) first to ensure that alone isn't the problem.

It's unclear. The CEM/BCM would be more than that. Get the part numbers.

Outcome

Good day. I was having the same issues on my 11' sportwagen and noticed these posts. Curious as to the results of all the work?
I recently had my ECU replaced in hopes that solved the issue, but unfortunately not. Seems like I may have faulty relays somewhere.

Any direction would be greatly appreciated.

Mario

Hello,
I have a 09 Jetta TDI doing the exact same thing as described on this post; any updates on resolution would be much appreciated.

Im having the same problem on my 2006 Jetta TDI seemed to coinside with a cold snap. The temperature outside was about 5 degrees and then it went down to -2 (Celsius) and that’s when this problem started. Did you change the ecu? Did it fix the problem?