ethanasi

I had a failure in the AUX battery (red sign almost every day).
I drove with the red sign and I had some more lights on. The engine light was ON and SBC is not working.
The most worrying problem is that I was stuck in the first gear. I couldn't even go to R without turning OFF/ON the car
Now I replaced the AUX battery. The SBC started working again (SBC H for example) and also the gear shift is working.
Is it possible that the problem with the gear shift was caused by dead AUX battery? Or do I need to replace the gear electric board?
Thanks!

ethanasi

After some reading, I have seen that AUX battery can cause the car to go to "limp" mode, so, finger crossed, I hope I resolved the problem with replacing the AUX battery.

kajtek1

It is not that battery itself will put car in limp mode, but MB made several idiot-preventive programs in the cars, that will force neglecting driver to take care about the safety-related repairs.
You are the 2nd guy on forums, who went so far with red lights on the cluster and I think now you need SD to reset the system.

ethanasi

Thanks for calling me that :-) , but, instead of red lights, wasn't it better for idiots writing:
"Your auxiliary battery is failing! We are putting the car in limp mode until you go and repair the fault"
Or, it would take a lot from $200 diagnostic AutoStar miracle?

Russell Ormerod

No aux will not cause limp mode, but SBC service limit will

kajtek1

For the record - I did not call you anything. . I posted simple technical conclusion.
Your suggestion would be nice, but I see 3 obstacles.
1. the cluster LCD doesn't have that much letters in it.
2. letting owner know what is happening with the car would put dealers out of bussiness
3. European culture is different, so not only manufacturers expect from the user more knowledge, but the "political correctness" is less observed and when you screw something up, you have good chance to hear direct comment.

ethanasi

I fully understand what you're saying, and I can see why MB is keeping codes "secret", so I am not pushing this discussion any further :-)

Going back to my problem, my 3$ ELM327 reports:
p0705 - transmission range sensor circuit malfunction prndl input
and it cannot be cleared.
My mechanic is saying that I need to replace the whole Gear Shift module :-(

ethanasi

Just the follow up:
I replaced the Gear Shift module and everything seems OK.

MAR12

hi i have a c class c180 (w)240 which has a 12v 12ah 170 amp battery in the boot when i test the battery voltage at the terminals is 11.4v on aux battery when testing at main terminal on 13.6v the aux battery relay main voltage is 13.6v this is when engine is running when accelerating car goes into limp mode NB ECO light stays yellow on dash the gearbox jerks in gear then goes into limp mode STOP /START and HOLD assist not working at one stage when driving off and auto door lock comes on all these symptoms happened at the same time Extra info using AUTEL MaxPRO following fault codes P033904 U41600 U010100 on previous dignosis fault TCM module overvoltage fault whic led me to check aux battery system

CaliBenzDriver

I would recommend you try fixing the cause of 11.4V... nothing good happens under dismal start/run voltages.

The AUX voltage says healthy!

What are those DTC pointing you to?

Stan87BG

I had red ligh visit workshop. My aux battery was completely dead. My transmission wasn't good. Always after acceleration the transmission was sticking on2nd gear. I change the battery and everything goes back to normal.

Etimram

CaliBenzDriver

Redlining your limp mode engine... my call for action
Hear this to save your some resources:

TIP #1: TEST!
batteries are not cure-all mistery containers.
Test batteries are being charged by car.

You can test parts before replacing or you can test 'em after. This is where MB shops and DIY'ers stories usually fork apart.
DIY path is an opportunity to learn a thing or two or surrender to pros.


TIP #2: TODA..!
You know about putting 2 and 2 together, right? Prepare some joy....

I think actually we have a cause for celebration: your flat battery is the smoking gun for your limp mode.

DC POWER is not reaching all circuits and undervolting major modules (Gear selector, Steering, Ignition,...) - These smart modules thrive on clean power to exchange clean data. The current power chaos is impacting that process.

Here, we're gona give ourselves a break.

A > I dont know what power handler part is toast. Like some kind of power relay..??

B > I don't know what modules share that poor voltage supply. Get your car alternator power distribution diagnosed.

With answers to A + B your car will be back in the fast lanes.

(In memoriam of how wide the crying skies opened up this morning to welcome the departed spirit we sent)