Topic: 5F: Information Electr. faults

I have discovered that I'm getting the DTC below on start-up. No other symptoms. I assume that this is just a side-effect of having the FIS-Control unit between the MMI unit and display. Is anyone else seeing these?

04142 - LVDS Line for Display Module
            011 - Open Circuit - Intermittent

Re: 5F: Information Electr. faults

I don't know how your headunit tries to detect an open circuit.
The FIS-Control MMI uses decoupling capacitors in the LVDS lines. For DC current a capacitor looks like an open circuit.
Maybe that is the reason.
But not all headunit seem to test this. I do not see this DTC in my car.

Re: 5F: Information Electr. faults

I have two modules in series between the MMI and its display: fis-control mmi and a video interface, I have no DTC

4 (edited by Lightningman 2018-09-12 10:49:04)

Re: 5F: Information Electr. faults

Hello,

stefan@fis-control wrote:

I don't know how your headunit tries to detect an open circuit.
The FIS-Control MMI uses decoupling capacitors in the LVDS lines. For DC current a capacitor looks like an open circuit.

Stefan are you using DEcoupling (cap on signal
to ground) capacitors in the LVDS lines or are you
using COupling (in series with the signal line)
capacitors? I suspect the latter since you you
don't want to burden a digital video line with
extra capacitance (slows switching times AND
deforms the orginal signal form).

Either way, however, a capacitor will act as a dead
short when applying DC to it. At least until the
charge on the capacitor plates has been equalized.
After that it looks like an open circuit until charge
on the plates is no longer equal. This is why you
can use a capacitor as a resistor in AC circuits.

However, I don't think that the ECU is this quick
(cap charge time) in filing a fault code.

I think the ECU simply monitors the current that
the LVDS driver circuit is taking up. If it is too
low than it says open circuit. If it is too high it
says short.

As to Dippy's question: I would suggest checking
the four HSD plugs involved (Naviceiver to FC MMI
and FC MMI to Monitor MMI), Maybe one of the
interlocks did not snap in correctly and this is why
you get an open circuit once in a while. If your are
really out of luck it might be that one of the
four pins (in each HSD so a total of 16 fault
possiblities big_smile ) isn't crimped correctly. This would
mean cutting the plug off and putting a new one
on. I absolutely detest even actually execrate
crimping. It is fast, but a real man's connection is
done using solder and a hot iron big_smile

Audi A6 / BDG 2,5 TDI Bj 2003 // Mj 2004 Bekennender FIS-Control Junky ;ö))

Jetzt auch mit A6 4G Avant Bj 2013 unterwegs // Fzg. *NOCH* ohne Mods ;ö))

Re: 5F: Information Electr. faults

Thanks for all the advice. I could have lived with the DTC if it was just a side-effect, but now I know it's not, I guess I'll need to open it up and check the connectors. I definitely wasn't getting the DTC prior to installing the FIS-Control MMI so if there is a bad connector it has to be with the new equipment.

Re: 5F: Information Electr. faults

@Lightningman: You are correct, the capacitors are in line with the LVDS signals.

Re: 5F: Information Electr. faults

Stefan, I have done some testing on this today and can conclude that this is a systematic fault. Here's what I did:
1) Checked for DTCs and found this one with a count of 28 and dated 9/9/18 (the last date that I used VCDS and cleared all DTCs)
2) Cleared the DTC. Cycled car power and checked again. DTC had returned with today's data and a count of 1. Cleared it.
3) I temporarily removed FIS-Control MMI from the display, restoring the MMI to "stock" connection.
4) Powered up car and checked VCDS. No DTC. Cycled power. No DTC. Once more to be certain. No DTC.
5) I carefully inspected all the cables and connectors and they looked OK. Then I reconnected FIS-Control MMI, but decided to "swap" the ends of the cable just in case this would make a difference.
6) Powered up car and checked VCDS. No DTC.
7) Cycled power. This time the DTC had returned. Cleared it.
8) Repeated this power cycling several times, taking careful note of the time of power-down and up again.
9) On each check there was the same DTC with a count of 1, corresponding to the exact time I turned power OFF.

To me this suggests that there is no bad connection, but that for some reason there is an incompatibility between FIS-Control MMI and my specific car in the way that the power management system turns off the power.

Since this DTC is the only symptom and FIS-Control MMI appears to work as expected, I guess I don't need to worry about it. However I would appreciate it if you could track this as a genuine customer issue - maybe it can be fixed in a future revision of the hardware?

For reference here's the full detail of the DTC:

1 Fault Found:

04142 - LVDS Line for Display Module
            011 - Open Circuit - Intermittent
             Freeze Frame:
                    Fault Status: 00101011
                    Fault Priority: 6
                    Fault Frequency: 1
                    Reset counter: 136
                    Mileage: 23600 km
                    Time Indication: 0
                    Date: 2018.09.22
                    Time: 17:05:14

             Freeze Frame:
                    Voltage: 12.00 V

Re: 5F: Information Electr. faults

Thanks for the investigation.
As the timestamp of the DTC is the exact time when you turn off the ignition, this might be an explanation.
The FIS-Control MMI is powered with ignition (Clamp 15). That means, at the moment you turn off the ignition, the FIS-Control is dead immediately and its onboard LVDS transmitter is off. If the headunit checks the LVDS connection only one second after the ignition is off, it will detect a problem.

What you could try is, to turn off the headunit with a long press on the volume knob. This will also turn off the display, but as the FIS-Control is still powered on, I don't expect a DTC in this case.

If I get feedback about that DTC from other users, I will report here.