UCDS Forum

Hi all

I have the following DTC from the last six months. It's related to Auto Start/Stop.
Auto Start/Stop is not working and the OFF led on the Auto Start/Stop button is always active.

DTC Error read - BCM
DTC Errors: 1

B12CD - Voltage Quality Module
Status: 87 - Missing Message
Ext.Status: 2F - No Communication Or Incorrectly Connected.(DTC) Present at Time of Request.

Any ideas on why this DTC is present and what can be done to resolve it?
Thank you.

P.S. The battery is fully charged several times to see if this is the issue. But even then and clearing the DTC did not help.

Finally I managed to get the Auto Start/Stop system working again!

I did a lot of debug with FORScan and other tools and also tried out a nearly new battery suitable for Start/Stop systems including resetting Battery Monitoring System, all of which did not help.

I was suspicious that the Start/Stop module (Voltage Quality Module) is stuck in a state and that I did not wait long enough between disconnecting my battery and connecting a new one for the module to power-reset fully. Today, I just pulled-out the fuse of Start/Stop module in the engine compartment (F11 rated at 30Amps --> this might be different for you, please check manual supplied with the car) and verified with a multimeter that it was intact. Started the car still with the fuse pulled-out, the instruments (dash, climate, etc.) did not turn on as expected because they are linked to the Start/Stop system. Turned off the car, waited a couple of minutes and inserted the fuse back.

Started the car and the OFF led on the Start/Stop button is not longer active as it was before indicating that the Start/Stop system is active. In other ways, activating Active Park Assist should deactivate the Start/Stop system (OFF led active).

After driving for a about 10-15km, the Start/Stop system kicked in when stopped at a traffic light

Usually, I disconnect the battery or fuses first to power-reset the modules in case of malfunctions or abnormal behaviours,. But, somehow this time I sort of missed it!