Insufficeint PS current corrupting flash?
Thread Starter
Member
Joined: Feb 2024
Posts: 77
Likes: 37
From: California
2005 SL55 (past), 2021 E53 (present)
Insufficeint PS current corrupting flash?
The key and door buttons will not open the trunk after a rear SAM flash with a 20A power supply on a 2021 E53. Does it make sense that the 20A supply is the reason the Rear SAM flash corrupted, and the trunk failure is a direct symptom of that?
It's not a mechanical issue and it's not a wiring wiring issue because the trunk will open with Xentry. Seems like insufficeint current leading to a volltage drop while flashing.
It's not a mechanical issue and it's not a wiring wiring issue because the trunk will open with Xentry. Seems like insufficeint current leading to a volltage drop while flashing.
Super Member
Joined: Jun 2025
Posts: 784
Likes: 248
From: USA
Absolutely. That's a classic symptom. 20A is not enough for a modern SAM. During the flash, the module draws a heavy surge. The voltage drops, corrupts the data, and bricks partial functions. Always use a proper, high-amperage power supply or a charged battery maintainer. You'll likely need to re-flash that SAM with adequate power.
MBWorld Fanatic!
Joined: Dec 2011
Posts: 1,692
Likes: 488
From: Spain UTC/GMT +2 hours
W213 All-terrain
Any Flash file has a Checksum and a digital signature and those are checked by the micro-controller of the respective module.
Most of the micro-controllers use a Boot SW and one or more Data/Programs SW's. In most of the cases, if one of the SW's become corrupted or is not suitable for the respective HW/Configuration, after the Restart the module become non-functional but reachable by the Diag System.
When the main SW/Program is not corrupted, digital signature and or Checksum is OK, the "Diagnostic Variant " ( this is like a name of the module showed in Xentry on first page when the module is accessed ) it will be like thi, for example: DRVU_NG_AD1_1A0 - where DRVU_NG is the module and the AD1_1A0 is the Diag Version of the firmware
When the SW/Program is corrupted, the name of the module will be like this: DRVU_NG Bootloader mode.
Meaning the module just boot into a bootloader mode only to be accessed by the Diag System for correcting the failed SW Flash.
Also, as many of the modules share the same HW ( PCB with components ) most of the modules can be configured over different SW's to match the vehicle and / or options. Because of that, using a wrong SW for your car or for your car options, but compatible with the HW number of the module, the Flashing can be successful, the signature will match and module will start but with some function not available of course.
Most of the micro-controllers use a Boot SW and one or more Data/Programs SW's. In most of the cases, if one of the SW's become corrupted or is not suitable for the respective HW/Configuration, after the Restart the module become non-functional but reachable by the Diag System.
When the main SW/Program is not corrupted, digital signature and or Checksum is OK, the "Diagnostic Variant " ( this is like a name of the module showed in Xentry on first page when the module is accessed ) it will be like thi, for example: DRVU_NG_AD1_1A0 - where DRVU_NG is the module and the AD1_1A0 is the Diag Version of the firmware
When the SW/Program is corrupted, the name of the module will be like this: DRVU_NG Bootloader mode.
Meaning the module just boot into a bootloader mode only to be accessed by the Diag System for correcting the failed SW Flash.
Also, as many of the modules share the same HW ( PCB with components ) most of the modules can be configured over different SW's to match the vehicle and / or options. Because of that, using a wrong SW for your car or for your car options, but compatible with the HW number of the module, the Flashing can be successful, the signature will match and module will start but with some function not available of course.
MBWorld Fanatic!
Joined: Oct 2019
Posts: 5,152
Likes: 1,766
From: Colorado
G550
I'm still curious about why-for the 20 amp power supply. Likely it's a switch mode device, and they're notoriously noisy and usually have poor transient regulation in response to surge currents. Trigital raises legitimate concerns about flashing errors arising, despite safeguards intended to detect and prevent such. I recall a post of several years ago in which BenzNinja advised against wireless (Bluetooth) OBD dongles because they introduce unnecessary risk in transferring files. I successfuly disabled *** with a recoding, and that's as much as I want to gamble.
MBWorld Fanatic!
Joined: Dec 2011
Posts: 1,692
Likes: 488
From: Spain UTC/GMT +2 hours
W213 All-terrain
I'm still curious about why-for the 20 amp power supply. Likely it's a switch mode device, and they're notoriously noisy and usually have poor transient regulation in response to surge currents. Trigital raises legitimate concerns about flashing errors arising, despite safeguards intended to detect and prevent such. I recall a post of several years ago in which BenzNinja advised against wireless (Bluetooth) OBD dongles because they introduce unnecessary risk in transferring files. I successfuly disabled *** with a recoding, and that's as much as I want to gamble.
MBWorld Fanatic!
Joined: Oct 2019
Posts: 5,152
Likes: 1,766
From: Colorado
G550
Why is the battery not sufficient? The SAM uses 5V or 3.3V logic circuitry and has its own internal voltage regulator(s) that drop 12V down. There's a lot of margin before a dip in the 12 volt supply affects the logic voltage. If the battery is fully charged, current surges shouldn't be a problem. Connecting an external supply for a short SAM flash seems unnecessary, unless the car is being worked on for several hours continuously and it's drawing down the battery.
MBWorld Fanatic!
Joined: Dec 2011
Posts: 1,692
Likes: 488
From: Spain UTC/GMT +2 hours
W213 All-terrain
The flashing programs have 11,5V lower limit. As all automotive modules doesn't use simple "step down" circuit. An ECU use very complex, monitored, filtered, cooled, independent power source controllers.
Trending Topics
Thread Starter
Member
Joined: Feb 2024
Posts: 77
Likes: 37
From: California
2005 SL55 (past), 2021 E53 (present)
Because compliance. If the load demands more current than the power supply can deliver, the power supply voltage will drop. As the power supply voltage drops, all circuits it powers are also susecptible to voltage drops. It's hard to say exactly what will happen. Maybe nothing, maybe a bit error, maybe total system shutdown. By providing adequate current, you guarantee voltage levels stay high enough to prevent such problems. You cannot rely on a car battery to meet the demands of OBD circuits. Because a car battery was designed for quick bursts of current, not sustained loads. Hence, a power supply is always necessary.
How much power supply current is enough? I don't know. @trigital gave the right answer. More is better. You can't have too much current. But for sure, you can have too little.
How much power supply current is enough? I don't know. @trigital gave the right answer. More is better. You can't have too much current. But for sure, you can have too little.
MB World Stories
The Best of Mercedes & AMG
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
10 Most Reliable Mercedes-Benz Models You Can Buy Used
Verdad Gallardo
MBWorld Fanatic!
Joined: Dec 2011
Posts: 1,692
Likes: 488
From: Spain UTC/GMT +2 hours
W213 All-terrain
On modern cars the connection between diagnosis system or flashing programs to a specific ECU is not a direct connection.
The Diag sys did not directly "talk' with any particular ECU except CGW ( Central GateWay).
Diag ask CGW to Broadcast needed messages to the particular ECU.
During the Flashing session, CGW could cut the communication with some of the ECU's sustaining only the communication with the requested one.
This is the moment when ( depending of the car topology ) wipers start to run at maximum or the Engine fan become erratic as in some particular cases Front SAM is disabled by the CGW and wipers starts or Engine ECU is disabled for letting free the CAN for Gearbox Flash.
Of course, all that increase the electrical burden of the battery.
In my workshop I use Gysflash 100Amp ( inteligent switching power supply ).
The Diag sys did not directly "talk' with any particular ECU except CGW ( Central GateWay).
Diag ask CGW to Broadcast needed messages to the particular ECU.
During the Flashing session, CGW could cut the communication with some of the ECU's sustaining only the communication with the requested one.
This is the moment when ( depending of the car topology ) wipers start to run at maximum or the Engine fan become erratic as in some particular cases Front SAM is disabled by the CGW and wipers starts or Engine ECU is disabled for letting free the CAN for Gearbox Flash.
Of course, all that increase the electrical burden of the battery.
In my workshop I use Gysflash 100Amp ( inteligent switching power supply ).
Thread Starter
Member
Joined: Feb 2024
Posts: 77
Likes: 37
From: California
2005 SL55 (past), 2021 E53 (present)
@streborx, I see how you are looking at it. The car battery has 12V so isn't that good enough for a 5V circuit? Probably. It's not yes for sure because the battery could be weak. But even if the battery is in great condition, it is still unregulated and that's a potential problem for other circuit demands during Xentry. For example, a fan switching on will cause a large inrush current spike that an unregualted source may not be able to deliver. If the battery cannot deliver this inrush current, then where else will it come from? The path of least resistance. In other words, anywhere it can, which includes capacitors that stabilize the microprocessor power. You can't have that. In this way, it’s the lack of current that will cause the ECU voltage to drop below 5V.
Last edited by Scallawalla; Feb 5, 2026 at 11:06 PM.
