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Case study: Faulty start-stop

By autotech-nic on November 2, 2020

Opus IVS 360 Master Technicians help a customer with a Mercedes-Benz, which has an inoperative ECO start-stop function

Opus IVS delivers beyond the scope of general scan tool diagnostic capabilities. Their IVS 360 Live Repair Guidance support service gives workshops access to the IVS 360 team of OEM experienced, factory-trained diagnostic technicians. Not only does the team help establish the fastest, most reliable, and accurate diagnosis, they actually take you through the process step-by-step, all the way through to the repair. Ultimately, workshops have access to a team of behind the scenes OEM brand-specific technicians that they can rely on daily to provide the actual fix.

Customers can access the IVS 360 team directly from their Opus IVS diagnostic devices. Using the diagnostic software from DrivePro, Autocom, Autoenginuity and extensive product knowledge, the team identifies the cause and steps needed to fix vehicle faults, helping technicians repair the most complex vehicles fast with live repair guidance.

Here is the latest case from the IVS 360 Mercedes-Benz team:

Make: Mercedes-Benz

Model: Mercedes-Benz A class (W176), B class (W246), CLA (W117) and GLA (W156) class vehicles from 2009-2015 up to 2019

Fault: Direct Starting/ECO start-stop inoperative

Fault code: B21059A current & stored in Drivers SAM (Signal Acquisition Module)


  • Normal engine starting via key or ECO stop/start failure
  • Fault code B21059A “The capacity of the starter battery” is too low
  • The operating conditions for the component or the system are not satisfied is current and stored in the Drivers SAM (N10).

Possible causes:

  1. The charge level of starter battery is staying frequently between 55 <> 65% (State of Charge) leading to insufficient battery power.

In the current climate due to the COVID-19 Pandemic, vehicles are not being driven often enough to bring the required charge level above 80%. This fault may be triggered if the battery is constantly below 55%.

2. Battery has aged. EFB type batteries that are aging prematurely are now being replaced with AGM batteries.

Repair steps:
Check the battery type, try to fully charge the battery with a smart charging battery station and re-test the battery.
“Confirmation of battery change” in the Drivers SAM under the ACTUATIONS menu should allow the fault to clear. Monitor and re-check the battery should the fault re-occur.

The Battery requires replacing.
Replace EFB wet battery with an AGM (Absorbent Glass Matt, also called Fleece) battery.

VeDoc requires amending, delete code 11O ~EFB battery installed.

Perform online SCN coding with Xentry Diagnostics / Pass-Thru or similar capable diagnostic equipment in the N10 (SAM) module. This will change the charging characteristics needed for the new AGM battery to operate correctly.

Confirm battery change in the N10 (SAM) under the ACTUATIONS menu.

For information on IVS 360 support, visit or email
01865 870 060



About Autotechnician
Autotechnician is a magazine published nine times a year, delivering essential information to independent garage owners and technicians in the UK. Delivered both digitally and in print, autotechnician provides readers with technical, training, business advice, product and news, allowing our readers to keep up to date with information they need to run and work within a modern workshop.
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