08 Jetta -- doesn't start, then does after key left in ignition
May 27, 2016 5:43 PM   Subscribe

08 Jetta, manual. Drove out to a store, parked, came back, wouldn't start, tried a bunch of stuff. Electrical system came on but no warning lights. Happened to leave the key in the ignition while discussing the problem and suddenly all the dash lights popped on, after which point it started fine. Drove home, turned it off, tried to turn it back on right away--same situation all over.

Some of the things we tried that did not work: The second key, wiggling the key (key turns all the way to the start position just fine), turning the wheel, pumping the clutch and/or break, swearing.
posted by anaelith to Travel & Transportation (14 answers total)
Does it think the key is a fake copy? I had a chevy malibu that would do that.
posted by Ms Vegetable at 5:44 PM on May 27, 2016

Yeah, this car is new enough that the key probably has a security chip in it. Sounds like (from the fact that the second key does the same thing) that the bit in the car that reads it is kinda borked.
posted by kindall at 6:04 PM on May 27, 2016

Are the battery cables secure on the posts?
posted by nom de poop at 6:20 PM on May 27, 2016

Is it diesel? If so, it's in the manual. You have to leave the key in the ignition to warm up coils? Sorry, my memory is hazy and the manual isn't with me at the moment.
posted by stoneweaver at 7:38 PM on May 27, 2016 [1 favorite]

VWs are somewhat notorious for electrical gremlins. I've had a similar problem, though with a 2000 Jetta. I believe the problem was corroded battery terminals in my case. I would definitely recommend checking the battery and terminals. I would also recommend looking into which relays could cause this sort of issue and checking that they are properly seated and not corroded. It is quite possible that one of the relays is sticking or otherwise not functioning correctly. Sometimes, you can replace one relay with another that is identical but in another position for testing purposes.

If you search on VWVortex or TDIClub, you will probably find others who have had the same problem and can offer solutions. You could also get the codes checked to see if anything has been recorded.

I think an issue with the key is much less likely to be the problem than any number of other issues.
posted by ssg at 10:39 PM on May 27, 2016

It is not a TDI, it is a normal gasoline vehicle.

We will try these things today and report back. The suggestion about checking the codes is great and we should be able to do that. As per normal, these things happen at the worst damn times.
posted by anaelith at 2:59 AM on May 28, 2016

Does the key require a battery? My '01 GTI key has a button battery inside and things can start acting up if it begins to die.
posted by Thorzdad at 5:33 AM on May 28, 2016

I had the exact same issue with an '03 Pontiac Grand AM GT. Wouldn't start for the key unless you left it in the "on" position for five minutes, and then you could start it with anything (intermittently at first, then constantly).

At the time, I referred to it as the car having Alzheimer's, but what was actually happening was a failure in the security reader in the ignition system being unable to recognize the chip in the key. When the mechanics eventually figured the problem out, it was far more than the car was worth to fix it, so they recommended just leaving five minutes early for any important appointments. It was aggravating, and I also tried swearing a lot, but better than spending $1k+ on a new computer.

I ended up donating the thing to charity for the tax write-off after it developed a few more expensive problems, but hopefully you have better car luck.
posted by the artless dodger at 6:21 AM on May 28, 2016

Happened to leave the key in the ignition while discussing the problem and suddenly all the dash lights popped on, after which point it started fine.

Hmmm. That's kind of hard to get - how do you know the electrical system came on beyond the dash lights? If it is because the fan started or something, then that's good. The ignition is coming on but the dash (and so by extrapolation ECU) is not working/operating. I'd be tempted to suspect the dash chip recognition module as well (as others have suggested). The fact the second key didn't work means it is more likely to be car than key, to me.

That's not to say that it may not be something dumb and simple and the 'leaving the key in' is just either coincidence (I've seen weirder) or symptomatic of a loose battery lead or earth that needed to warm up (through small current flow) to connect properly. I'd check all the battery live and positive connections at the engine, battery and chassis, remove - clean-refit and then try again.
posted by Brockles at 9:47 AM on May 28, 2016

Still sometimes not starting (but sometimes starting first try).

While it won't start, the air conditioning works, headlights, etc. But there is nothing displaying on the electronic display on the dash. The cue that it's ready to start is that the display part starts showing all the information.

Checked the battery as much as possible without disconnecting it, it was perfectly fine and fully charged. Likewise alternator seemed fine (had the reader connected while starting). Of course, it did start that time...

At one point we tried to jump start it while it wouldn't start--nothing. Eventually (while the cables were connected) it did it's normal dash comes on, ready to start routine and started.

At one point it stalled in traffic (probably but not conclusively operator error, there was a hill start involved) and refused to start again. Wait, dash lights come on after about a minute, starts fine, continue driving.

During one refusing to start session, some of the relays felt hot (ouch-y hot) while others were cool. Swapping some of the relays around did nothing, though. Temperature here has been summery/80s, but working/failing seems to have nothing to do with the engine/car temperature.

Still haven't gotten to pull codes from it or really pull the battery leads off and check the terminals (see above re: these things happen at the worst times). Gremlins.
posted by anaelith at 6:12 AM on May 30, 2016

Based on some similar videos around on the innerwebs, if it was the immobiliser, the lights would all be on and an icon and text for 'immobiliser activated' would be displayed. The complete lack of lights suggests a connection issue in the wiring. Either to power the dash or (more likely) to power the ECU. I'd check (and maybe just replace) the ignition relay and fuses. This may also be a broken wire feed to the ECU or similar. It doesn't sound like a simple thing like the immobiliser.

But I'd start with removal, clean and refit of the earths and power wires. It could be something as annoying as a dry joint in the ECU or something similarly expensive (maybe the dash itself), or it could be something as simple as a broken wire in the loom. It sounds like a difficult trouble shooting experience, though.
posted by Brockles at 9:45 AM on May 30, 2016

Also, several sources say that the immobilizer allows the car to start then immediately shut off. So that isn't the issue here. Forgot to put that bit in.
posted by Brockles at 9:46 AM on May 30, 2016

Possibly the security keys in some cars are designed such that, if the chip in the key doesn't pass the check, the car can still be started after a delay of some minutes. This would do as much to deter theft as refusing to start at all, but still gives you the ability to drive the car at some inconvenience (so you don't have to have it towed to the dealer, at least). To me, the behavior you're seeing still looks like a glitch in the security system.
posted by kindall at 11:21 AM on June 1, 2016

Car eventually just stalled while driving and wouldn't start, so it got towed to the shop.

It was a relay after all, but one that was buried behind the dash (power supply relay). Similar to this story, 10$ part, 1.5 hours worth of labor......

No error codes ever popped on the OBDII reader.
posted by anaelith at 2:55 AM on June 7, 2016

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