W211 SBC issues
Thread Starter
Newbie
Joined: Aug 2025
Posts: 4
Likes: 1
From: Vereeniging
W211 E270 CDI
W211 SBC issues
Hello
I have a 2005 E270CDi with 250 000 km. Help please!
Some time ago I had both batteries replaced and suspect a faulty auxiliary battery might be the cause of my SBC red warning today.
The red battery warning started coming on a few weeks ago after the car had been parked for a few hours and disappeared after a restart. Just for the same repetition every day. So today I got the dreaded red "reduced braking power" red screen. The brakes work fine and I can hear the SBC pump running in the same way and at the same intervals it's been since I've had the car (except from just before I had the SBC pump replaced about 2 years ago)
Since I started getting the red battery warning, I checked the voltage before and after engine start regularly and the charge seems fine at between 13.7 and 14 volts whilst driving. I also have no cold start issues despite the red battery warning.
It's booked in for Tuesday to have it properly diagnosed at a Bosch service center. But I'm curious as to whether anybody else has had this issue and whether I am on the right track by suspecting a lemon auxiliary battery?
Any help would be appreciated!
Kindest regards
Peet
I have a 2005 E270CDi with 250 000 km. Help please!
Some time ago I had both batteries replaced and suspect a faulty auxiliary battery might be the cause of my SBC red warning today.
The red battery warning started coming on a few weeks ago after the car had been parked for a few hours and disappeared after a restart. Just for the same repetition every day. So today I got the dreaded red "reduced braking power" red screen. The brakes work fine and I can hear the SBC pump running in the same way and at the same intervals it's been since I've had the car (except from just before I had the SBC pump replaced about 2 years ago)
Since I started getting the red battery warning, I checked the voltage before and after engine start regularly and the charge seems fine at between 13.7 and 14 volts whilst driving. I also have no cold start issues despite the red battery warning.
It's booked in for Tuesday to have it properly diagnosed at a Bosch service center. But I'm curious as to whether anybody else has had this issue and whether I am on the right track by suspecting a lemon auxiliary battery?
Any help would be appreciated!
Kindest regards
Peet
Member
Joined: Jul 2006
Posts: 169
Likes: 6
Absolutely...
I've had all those symptoms you describe, as well as the car going into "Limp Mode", all due to a discharged aux. battery.
Worst case scenario, go buy a new YTX14-BS AGM (motorcyle / powersports) battery before spending 3 times the cost of the battery, to have it diagnosed at the service center.
I've had all those symptoms you describe, as well as the car going into "Limp Mode", all due to a discharged aux. battery.
Worst case scenario, go buy a new YTX14-BS AGM (motorcyle / powersports) battery before spending 3 times the cost of the battery, to have it diagnosed at the service center.
Thread Starter
Newbie
Joined: Aug 2025
Posts: 4
Likes: 1
From: Vereeniging
W211 E270 CDI
Absolutely...
I've had all those symptoms you describe, as well as the car going into "Limp Mode", all due to a discharged aux. battery.
Worst case scenario, go buy a new YTX14-BS AGM (motorcyle / powersports) battery before spending 3 times the cost of the battery, to have it diagnosed at the service center.
I've had all those symptoms you describe, as well as the car going into "Limp Mode", all due to a discharged aux. battery.
Worst case scenario, go buy a new YTX14-BS AGM (motorcyle / powersports) battery before spending 3 times the cost of the battery, to have it diagnosed at the service center.
Many thanks for the help - I really appreciate it. I will know Tuesday when it has gone for testing.
Kindest regards
Peet
Super Member
Joined: Aug 2004
Posts: 545
Likes: 87
From: Southern California
I have a feeling your alternator voltage regulator is worn out if you are only getting between 13.7 to 14v while driving, I believe that is on the low side. You should be above 14v easily.
Also, I would highly recommend using a CTEK battery charger to keep both the main battery and aux battery fully charged. These cars do not like having a weak battery.
Also, I would highly recommend using a CTEK battery charger to keep both the main battery and aux battery fully charged. These cars do not like having a weak battery.
MBWorld Fanatic!
Joined: Jan 2014
Posts: 3,969
Likes: 1,317
From: Republic of Texas
'99 and '05 E55 AMG
Scan the car with a diagnostic system. It will literally indicate to you what is causing the SBC error.
You can purchase an inexpensive battery tester and test both batteries yourself for 1/3rd the cost of a shop diagnostic fee. I use a Solar BA-5 myself.
You can purchase an inexpensive battery tester and test both batteries yourself for 1/3rd the cost of a shop diagnostic fee. I use a Solar BA-5 myself.
