Hi all,

Since 2 weeks I'm the proud owner of a 10 yo Octavia. She's got 182000km on the clock and I got 2 months of warranty from the 2nd hand car dealership I bought it from. So far I've driven 700km and gotten a number of errors and warnings, of which I believe the misfires to be the most serious. I'm trying to understand what could be the issue with the car so I can better understand when a dealership is just trying to dodge having to pay, or when they might have a point. I've gotten een OBDeleven to read out the fault codes.

I'll start with the easy one of which I'm semi-sure that it's not related to the other codes. 3 times in those 700kms I have gotten the dutch error: "Storing: werkplaats! Wagen alleen in positie P verlaten", which in English would be "Error workshop only leave vehicle in P position". The ODBeleven found a non active error code B116229, as I currently believe it's a common broken microswitch in the DSG stick that can be replaced. Am I correct in thinking that there's no real risk in letting this be for now, other than that the errors are annoying?

Then there is the Start Stop System. At the start of my drives the car indicates that the start stop system has an error. I find no error codes related to it, but I do think the battery voltage is a bit low with 13,9V when charging and 12,2V with the engine off 3 min later. There's some aircon energy management faults that also point towards the battery being on its way out. I'm mainly including this because it could somehow be related to the misfires in a way I don't understand.

Then for our main event the thing that actually worries me, the misfires. I had the car in my possession for 400km without this happening before, when after 20 minutes the engine suddenly started running very poorly. At the time I was doing 35 km/h in 4th gear. I pulled over and turned the engine off. When I restarted the issue was completely gone. I've driven 300km since without the issue reoccuring. Misfires were recorded in all cylinders. There's an active fault for 'Diagnotistic interface for data bus', U100800, that I can't find any info on. There is also an active fault saying there's no communication with the generator that could or could not be related.

I called the dealership, and they said that since the errors don't stay active on the dashboard of the car, they would like me to keep driving to see if anything sticks before going through the trouble of diagnosing. I'm trying to figure out if that is a reasonable call or not. Could the misfires just be a one-off that don't mean anything more serious?

Sorry for the overload of information and thanks for bearing with me!

Sidenote: The misfires happened before I installed a newer OEM multimedia screen and some software updates.

Hello and welcome.

I think you're fundamentally right about dodging the simple stuff and focusing on the misfire, though that gear selector micro-switch is probably worth sorting out quickly, IMO.

When was the car last serviced?

Plugs, lead, coil packs might all be a problem at that sort of mileage if not already replaced/serviced, though the power cycle reset seems to suggest it's an intermittent fault, not just faulty old parts. I don't know the dealer, but I would be pushing them to either sort out the problem now, or extend your warranty for this issue if they insist that you have to keep driving it to get more data on the fault.

Thanks!

They serviced the car when I bought it, but I don't think they touched anything ignition related. They did replace the timing belt and water pump.

Could the gear selector micro-switch result in something more serious? Good suggestion on the warranty, sounds reasonable to me to suggest they fix battery and micro switch and extend the warranty on the misfire issue.

Yeah. Well the park selector error is just as you say, no harm on that.

The others poibt towards battery, BUT generator no comms, maybe the root cause, you need to investigate that.

I'd resolve that first and see if misfire problem remain. Seems unlikely all 4 plugs or all 4 coil packs would suddenly go intermittent faulty. But I couldn't say for sure.

Have you had a look at plugs, when were they changed?

Strongly recommend investigating the alternator comms fault and a proper test of the battery.

There may be a date stamped into the top face of battery negative terminal to indicate its age.

I have seen references to misfires being caused by failing battery.

Thanks for the replies. I agree that the no comms fault of the generator is suspicious. I'm hesitant to take things apart as I'm still under waranty, but when opening the hood I find no loose connectors around the alternator. I haven't had a look at the plugs but will do later today, that I do dare to do myself 😄. Will check for battery date as well.

Does your stop/start function operate correctly?

Had a look at the battery, no stamped date. Start / stop function doesn't work correctly, first I thought only at the start of the drive but now I also had it malfunction after 50km.

I just started the engine and although it seemed to be running OK stationairy, I got active faults for misfires through the OBDeleven. I opened up the live data and could see the misfire counts go up for all cylinders, but especially cylinder 4 stands out, as the count seemed to increase with several instances per second. When divided by stationairy RPM of 750 it misses like 1 in every 5. I wondered about the timing belt as it's just been replaced, not sure if I selected the right values but these seem well within 5 degrees.

Sound like I shouldn't gather more data but let the dealer deal with it.

Does your battery have the battery monitor sensor module still attached (and connected to loom) on the battery negative terminal clamp?

Edited 8 July, 20258 Jul by Warrior193
added information

If its under waranty I would definitley take it back to dealer. Dont touch anything yourself or let another garage (even AA/RAC) to touch it as the dealer may well come back and say the waranty is invalidated. If they don't fix it then I reckon you have grounds to return car for a refund.

Alasdair

1 hour ago, Warrior193 said:

Does your battery have the battery monitor sensor module still attached (and connected to loom) on the battery negative terminal clamp?

It does. I can disconnect the connector from it, then I get a fault for battery monitor communication. This fault is different from generator communication. When I plug it back in the error is gone.

I just drove home without issues. The misfiring faults become inactive when I start driving. On the highway everything was ok. When getting closer to home and hitting traffic, the misfires returned. Especially the count for cylinder 4 increases. Putting it in neutral and touching the gas pedal ever so slightly is enough to make the misfire counter stop, so it seems the misfires only happen at idle. When stopping, it takes a minute or so of idling for the misfires to return.

Like mentioned I'm not touching anything myself for now as to not void the warranty, I've gathered enough information to bring it in and let them handle it. This was educational though, I'll update you when I find out what the underlying issue was.

Edited 8 July, 20258 Jul by fristiprinses

So I dropped the car off at the dealer and went on a holiday, picked it back up today. On the phone they said it 'drives like sunshine again' and that the issue with the DSG stick microswitch didn't pop back up so that they couldn't deal with it, which I believe to be bull****. They somehow forgot I was coming in and apparently the person that dealt with it wasn't in, so the guy that gave me back my car couldn't tell me what had happened with it. They drove 300km with it and left me with an almost empty tank, nice one lads. They didn't clear any faults in the system it seemed, the 'Engine: Diagnostic interface for databus' and 'Gateway: Generator: No communication' are still active and present.

The car did drive well though, I didn't notice anything on the drive home, 30 minutes/35km mix of highway and city driving. No misfire faults became active again, but I did read the data and the total misfire count increased with about 10 for every cylinder on the drive home, except for cylinder 1 which racked up 90 misfires. I'll give the guy who handled it a ring tomorrow to find out what was replaced, but I have two questions I'd like to hear your opinions on:

1. The dealership seems to think that when the car drives fine and there's no lights/warnings on the dashboard, the car is fine and their warranty obligations have been fulfilled. Is this standard / reasonable? I on the other read the ODB warnings and have additional concerns. Am I expecting too much from 10 year old used car sale?

2. How many misfires are acceptable? Is there a point in bringing up that there's still some misfires happening?

If there are uncleared faults present and the engine is logging frequent misfires, the car is faulty. The supplier has had one unsuccessful attempt to fix, your next move should be to inform them you are rejecting it.

It is possible that your fault is something as simple as a faulty battery - your stop-start not operating could well indicate this, faulty battery can also be the cause of misfires.

Has the battery been tested by suppliers mechanic?

Finally got a text message from the guy saying they replaced plugs + coil packs. Everything has been such a hassle with them that I might prefer testing and potentiality replacing the battery myself. Might learn a thing or two while we're at it.