RACCAR

Ongoing intermittant fault in this car, A4 B9 2017 2.0 TDI QUATTRO. New battery and alternator fitted by dealer and this fault continues. This is the first time I have managed scan with obd 11 and catch the fault code P068400, glow plug control module to power control module no comms, and just throws the standard drive system malfunction fault and no Start, but suprised this dosent allow the car to start. Checked for parasitic drain, seems normal around 30ma after going to sleep, although it still seems to be related to voltage loss, if I give it a battery booster I can get it to start. Battery is brand new and was changed by the dealer a few months ago due to the same issue. I can give it a full charge to 12.5v put it back in the car and connect and have 11.8v after switching on the ignition, press the on button here the starter relay energise and then throws the fault.
It seems it could be a intermittant faulty ground, possibly around the engine and linked to the glow plug circuit, but without a garage and ramp this is difficult to check where this harness is grounding from the glow plugs. The car has never indicated a low battery voltage, although this seems to be the reason because of something else that the car will not start.
Had the same the previous day but with fault code P048000 Cooling fan control circuit 1, but that has disappeared after reset and trying to restart.
Any advise and suggestions would be appreciated.
Car is booked to go back to the dealer next week 4th time for the same problem over 5 months, hopefully they can find the problem, but would like to check a little further myself.

142 guy

I am out of my league when it comes to diesels; but, a couple of comments on your battery issue. Charging the battery to the point where its resting voltage is 12.5 volts is not a guarantee and then the battery is OK. The better test of battery condition is a load test which evaluates the internal resistance of the battery. The dealership, any good repair shop or an automotive electrical specialist / battery shop should be able to carry out a battery load test to assess its condition.

You said . Load current will cause the voltage on the terminals of the battery to drop; however, that voltage does seem rather low for just the ignition load. On gasoline engines, it is common for the battery terminal voltage to drop to around 10.5 volts when the starter motor engages; but, the starter motor draws 70 - 120 amps (depending on the motor) so that voltage drop is reasonable. If you can't arrange for an actual battery load test; but, you have access to a multi meter to measure voltage, have some one measure the voltage at the battery terminals while you engage the starting motor. If the voltage drops below 10 volts when the starting motor is operating the battery is no longer in good condition. Low voltage may be causing mis operation of the control modules. If the battery terminal voltage is good, then you could have problems with battery cable connections or grounds or lots of other stuff. However, your car is only 4 years old so it seems very early to start suffering from bad electrical connections unless you live close to the ocean (salt spray).

The Audi's charging system is overly complex (my opinion). It attempts to adjust the regulator voltage to compensate for degradation in the battery with age. When the battery and alternator were replaced, unless they went through the software reset procedure the charging system can kill a new battery quickly. Since it was replaced by the dealer, I would assume that they would go through the software reset procedure.

RACCAR

Thanks for the reply, I agree the voltage dipping to 11.8v seems to low and maybe throwing faults which are related to low voltage and not real. I had ruled the battery out as it is new, but there is a small chance the battery is still the problem. Yesterday I checked all fuses and that they are seated correctly, plus connections and harness to starter relay, glow plugs and glow plug relay in the plenum chamber. All looks good.

RACCAR

So took it back to Audi, they have made a new ground point in the lower boot compartment, I think they have also changed the battery sensor. The sales guy didnt have a clue about what was done and when i asked he just waved his finger around the negative terminal. When I saw the original point of negative ground it didnt look correct as it was on a sub film of chassis. As i say this has now been moved to a better place and so far no problems after 4 weeks. If anyne has a picture of their battery negative chassis ground connection it will be much appreciated.

142 guy

I have not seen all the vehicle service manuals in the world; but, so far the Audi / erWin documents have to qualify as the most confusing / hard to use that I have ever encountered. The documents are definitely not friendly for non VAG specialists. Part of that may be due to the fact that they try to have one document cover multiple years with a huge pile of variants in different markets.

Having vented, this is what I found for the battery ground connection. It is for variants 0K0, 0K4 and VH2. There is at least one other variant with the battery still up front; but, since you mentioned 'boot' I am guessing that does not apply.


6 is the bolted ground connection to the body.

I don't know where you are located. In North America it is easy to access a product called Gardner Bender Ox-Gard.
I use it extensively on bolted electrical connections or on any electrical connection where there is moderate mechanical pressure between the electrical contacts (between the base and sockets in traditional light bulbs). The grease has zinc in it which enhances the electrical connection when it is clamped between surfaces under pressure. Applying the Ox-gard on the outside of the bolted connection will protect the connection from oxidation; but, any old grease will do that.

If you think you have suspect ground connections, inspecting and applying Ox-gard between the contact surfaces may help with that.