Thread: Comand problem with wakeup line

Hi,

Hopefully I'll get some help from here about my problem which has been occuring 4 months. Whole time when I had this car.

First of all, car is MB E 270cdiA estate with 527 Comand APS system.
HU, CDC, CP, VCS, NAVI, AGW and HK sound system, NGT1.

History:
Car has been bought around 4 months ago.
Problem exists then, but not so often.
Comand started 9 of 10, but now 1 of 10 times.

AGW had SW version 9.3 and currently newest some from 2006 (latest)
NAVI has SW version 11, propably latest also.

These are error codes from *, translated from finnish to english.
AGW
D135 Wake-up short circuit to -
D136 Wake-up short circuit to +
D104 MOST-component in position 4 notifies ring cutoff
D103 MOST-component in position 3 notifies ring cutoff

About that wakeup problem.

Red light blinks on MOST bus from device to device, but no quarantine
that data is correct.
Electrical Wakeup line has short circuit.

When key is not in EIS, short circuit is with -.
When key is inserted and turned to position I and II, wakeup goes
short circuit with +.
It stays so until KI-gauge shows Audio -----, then some resistance
will appear.
When key is removed short circuit changes with -.

Then you are disconnecting devices one by one and between those checking status. Short circuit with - stay until every device is disconnect.
Then measure - and wakeup line no short circuit, so no wire breaks or nothing in physical lines.

Then start to connect devices one by one, no short circuit when all devices are connected.
Key inserted turn power one (position II).
-> short circuit with + -> no power key removed -> short circuit with -

Only way to remove that is disconnecting all devices again.

Resistance is measured from back of device connection on each device.
No short circuit with any pin...


This problem has been studied with dealer, independet MB repairshop, MB Finland forum also I.

Now I'm hoping to get help what to do or should I change audio system.

How to proceed?
What device should be changed?
Removing whole system and changing to another "normal" audio system?
AGW mailfunctions?
This seems to be more or less SW problem or some weird behaviour.

Still AGW is master and it cannot be woken with MOSTbus wake-up...

Thanks advance.

Try changing the head unit.

You are assuming that it could be the case.
It has sometimes went so that screen is black, but everything works.

When I had older AGW SW version, from EE menu can be seen that backlights was on error and startup failures.

HU is tricky to change due to fact I do not got any spare ones also
it costs so much here / on world compared to change whole system
which also upgrades sound system.

Can that HU tested somehow without e.g. *?
I beliave that system will not start if HU is looped.

Consider the problem is that your head unit fails to operate.

Maybe contact Navisworld and drive to Germany.

There has been lot of activities during summer vacation.
Now I have also tested some other ways to find out what unit is broken.
looped one by one MOST line and removing wake-up and power inputs.
Currenty only AGW and HU are "in place".
Still problem appears, so this could be after all that HU.
Those error codes D103 and D104 points connections problem at VCS.
This seems to be strange.

Have anyone opened HU unit and checking some electorinic problems?
What could be the reason that HU fails to operate?
Could it only be that LCD screen or those backlights?
Can those be replaced?

Everything can be replaced. Even a small resistor. But there is no information on how to find the parts for a good price.

Now I have been checking and studying whole system.
Then HU was disassembled.
Fan doesn't work, I replaced it with almost similar one.
No effect.
Also there can be seen that back off screen on front of "metal box" has
blacken like 2x2cm area. There is weak electronic burning smell.

EE menu earlier showed those backlight errors and DC errors.
Now I got feeling that some component has failed due to caused that screen backlight has broken.

Still MOST line component in HU gets current and it sends light to next Comand unit.

Whole system started better on winter time, not so well summertime.

Does this give any ideas what is broken?
What should I do?
Replace HU or replace whole comand system to another after market system?

I think you already know the answer.

Thanks.

I needed that someone verified also my assumptions.

Is there some possibility to get parts for HU from somewhere?

Originally Posted by Berglund

Thanks.

I needed that someone verified also my assumptions.

Is there some possibility to get parts for HU from somewhere?

As stated before. Every single part of a COMAND can be purchased some place in the world. You would have to find this information by looking at what the labels are on the item itself.

Sooner or later this will cost more than buying a working used unit.