Dr. Electrical Short, I Presume?

[mr. alaska]

Hello ladies and gents!

Been using the forum as a reference tool for many years now without registering, but I've finally run into an issue that has me pretty well stumped, so here I am.

Picked up an 01 A6 Avant (2.8 ATQ) a couple years ago, and been wrenching on small issues ever since. Couple of weeks ago, after letting the car sit over a weekend, I went to start it up. Car fired up, ran for about a second, then died. Cranking it again failed, and after just a couple tried, the battery (about 3 months old) died. Jumped it, and still no dice.

My first thought was "Well, it started at first, so...fuel delivery?" Hooked the batt up to a mobile jumper, and flipped the ignition to "on". Fuel pump primed just fine, and after a couple cranks, I pulled the plugs. Yep, def getting fuel to the cylinders. Pulled the throttle body to make sure there wasn't an issue there, again, seemingly no issues. I would assume that leaves spark. Haven't had a chance to test it yet, but I would assume if I've got fuel and air, spark must be the issue.

In addition, replaced the coolant temp sensor (O-ring had almost dissolved into the coolant line), and tested the engine speed sensor (it was operating fine). Still nothing.

Finally, to figure out what could be killing the battery so quickly, I hooked up the multimeter, and saw something is draining the battery, and fast.

I would assume this all points to a short, but I'd really like to avoid spending the time and energy running back and forth pulling a fuse, getting up to check a test light, then going abck and pulling another (also heard that method doesn't work well on these cars).

Any suggestions or thoughts would be greatly appreciated!

[Audi_Tech]

Is the car constantly starting then dying like an immobilizer issue?

Open the drivers front door and latch the door latch to be able to arm the alarm system. It should take a couple of minutes for all of the modules to go to "sleep" mode which is usually referenced by the LED on the d/s ft door blinking slowly.
Perform a voltage drop across all the fuses located on the d/s dash, all should be 0.0 Volts.
If you find a fuse that has a reading then reference that circuit in the wiring diagram to locate the culprit.

Where in NC are you located?

[mr. alaska]

Is the car constantly starting then dying like an immobilizer issue?

Open the drivers front door and latch the door latch to be able to arm the alarm system. It should take a couple of minutes for all of the modules to go to "sleep" mode which is usually referenced by the LED on the d/s ft door blinking slowly.
Perform a voltage drop across all the fuses located on the d/s dash, all should be 0.0 Volts.
If you find a fuse that has a reading then reference that circuit in the wiring diagram to locate the culprit.

Where in NC are you located?

Unfortunately, no, ever since it first cut out, it's never been able to start again. It'll turn over, but wont go bang. There'd been a faint burning smell in the cabin when driving for a few days before, but I'd attributed it to a rear O2 sensor wire that had come loose and fallen on the exhaust. Tested, rewrapped and ziptied that back in place before this new issue came up.

I'm down in the refugee camp for Northerners, Charlotte (NC native myself though)

[Audi_Tech]

See if you have a signal from your crank sensor via measure values if you have a Vagcom as this sensor is the trigger for the ECM to fire the spark.
Can you try looking by the RPM gauge but I've been burnt by that before.

[mr. alaska]

See if you have a signal from your crank sensor via measure values if you have a Vagcom as this sensor is the trigger for the ECM to fire the spark.
Can you try looking by the RPM gauge but I've been burnt by that before.

Tested resistance on the crank sensor per the shop manual (debating whether to drop the moolah on VAGCOM, just using a multimeter for now) and it was good. I don't get any movement in the tach when cranking, but I wasn't sure if that's normal for the car or not. Wish I'd paid attention to whether or not it was when the car was still running, but oh well.

[Audi_Tech]

Pull a coil off and insert a spark plug.
Ground the spark plug to the valve cover and crank it over.
If you have spark then the crank sensor is good.
Post back results.

[mr. alaska]

Finally got around to testing, no spark on any cylinder. I try to avoid throwing parts at problems, but found a bosch crank sensor for 15 bucks and snapped it up, so we'll see if somehow I misread/mistested the sensor when it shows up Thursday.

[mr. alaska]

Been a long long time since I posted on this issue, and not a big fan of bringing dead threads back to life, but I figure closure can't hurt. Plus maybe someone will have the same issue in the future and find the thread of some use.

Let the car sit for a long time while I puttered around and did other minor work before taking it somewhere to get diagnosed.

Turns out it was a combination of issues with the alternator. The thing was dying, and would only charge the car when it wasn't under any sort of load. So basically, it had been running on battery power alone most of the time in the few days before it gave up. On top of that, it was shorting out, and draining the battery at rest as well, so double whammy there.

Result: New alternator, new battery, and now, a running car.

Side note: Reregistering a car in state of North Carolina is one of the biggest bureaucratic nightmares I've ever gone through, and I work for a company that pretty much deals in laws and regulation as its bread and butter...took almost a week of multiple trips a day to the DMV.

[Audi_Tech]

Glad to hear you got it sorted!
The DMV is satan's asshole for sure!