Alarm going off, esp and dpf lights

Pswaz

Audi a3 2.0 diesel 2007, had some work done around the alternator after a bolt snapped off the tensioner bracket over a week ago.
Drives fine for 1 week then one day...
The alarm goes off while parked doing nothing. So I go out and start the car and it's going loco. Esp light. Dpf light (pretty sure dpf was removed years ago) and clicking. I called breakdown who said the steering angle sensor was throwing up an error and not re aligning, cleared the faults and it drove alright for a while. Now back to alarm going off, esp and dpf lights. Cuts out the odd time too. Any ideas what this would be?

AdrianC

Could be as simple as the battery being a bit low voltage - that can cause all sorts of computer-related shenanigans.

How old's the battery, and did it get flattened while you were having the problem with the alt tensioner?

Pswaz

That's what I'm thinking. The battery is 2 years old. The alternator has stopped working twice in it's life. It didn't get flattened either time. I had it tested and all good apparently. But I'm thinking it's possible that test might not show other damage to the battery

AdrianC

Relatively cheap bit of trouble-shooting, isn't it?

Start with a good charge off the car. That may help initially. If the symptoms go away, then come back, replace.

Pswaz

Yep. Planning on swapping out the battery as soon as I logistically can so I'll let you know, appreciate the extra vote of confidence. Out of interest have you ever seen the battery test pass fine and yet replacing the battery solved some issue?

AdrianC

Define "battery test"... Low voltage is the main thing that's going to set the computers in a tiz. Weakness in delivering a hefty load (like the starter) could well dip the voltage low enough to still start, but cause things to sulk.

Pswaz

I didn't take a copy of the test result but I remember the operating voltage being fine and the starter voltage being a bit lower but still ok apparently. I don't have the numbers. The breakdown guy did say the starter will probably be soon on it's way out given the age and mileage. If the battery doesn't work maybe try the starter next.

AdrianC

Few quid on a ciggy socket voltmeter from ebay... You can see exactly what's happening while cranking.

Pswaz

Put a new battery in it. Still exactly the same. Have had to disconnect it again to head out for the night so the alarm doesnt go off. Surprised the new battery made no difference. I wonder if the steering angle sensor could be causing all this, but how would it cause the alarm to go off? And it would be a coincidence for that part to fail 1 shortly after the major work around the alternator.

angrycrow

The audi alarms are prone to failing internal batteries which manifest as the alarm going off randomly. A new sounder unit is about £80 but it is possible to cut the old one open and retro fit new nicads in the housing. I need to do mine as it keeps going off randomly. Could be the battery dropping voltage finished off the batteries in the alarm unit.

If you have ruled out the main battery the other issues could be one of the many control modules failing. You need to establish which module all of these functions are connected to, given dpf issue I would assume the ecu. Do you know anyone with vagcom, vcds as this would help pin point the issue. Might be worth a shout on audi-sport.net forum.

Is it your esp (electronic stability control) light or your epc (electronic power control) light. They look very similar bit mean totaly different things.

Epc means the car detected a fault (the dpf perhaps or steering angle sensor) so it limits the power output to avoid further harm to the engine.

Pswaz

Definitely Eps. Yes finding what's causing all 3 will be the thing, so I'm planning to get it plugged in this week.

I don't know a lot about cars, but the guys that did the work replacing the tensioner bracket did a few things to not inspire me with a lot of confidence tbh. Like, the work just got delayed every day, they left the undercar shield in the boot, didn't replace the battery clamp, messed up the (500quid) bill, and a plethora of other small errors, and they were only the ones I knew about. Took a week. This is true... the minute I got the car home I rang my insurance to check breakdown cover.

So I'd be fairly sure that whatever they did would be connected to this problem, and the ECU is one thing that would certainly wrap up all 3 symptoms, but then at the same time how on earth would they have goosed the brain from that work they did? Is there any other plug or something physical that could have been badly reconnected causing this? Guessing the ecu would be expensive and one of the last things to replace unless it's a real hum dinger.

Appreciate the support, when I do get the vagcom itll be great to ref this thread :beer: