P0562 on Mercedes-Benz: How to Diagnose & Fix

The EQE keeps its 12V AGM battery topped up from the HV pack through the DC/DC converter, but only when the vehicle's control units are allowed to sleep. Owners report telematics and comfort modules that never enter sleep — triggered by scheduled departure/preconditioning times, Mercedes me app polling, or an aftermarket OBD dongle — which drains the 12V overnight and, in the worst pattern, makes the HV pack cycle repeatedly to nurse a weak 12V. These triggers come from owner reports; no manufacturer bulletin confirms an OBD dongle or app polling as the root cause. The result is roughly 1-2%/day standing loss in owner reports (against a normal figure well under 1%) or a car that is simply dead in the morning with a 12V warning. A weak 12V also cascades: door handles won't present, the charge flap won't unlock, MBUX won't boot.

The EQS SUV's 12V auxiliary battery supports the entire low-voltage network - Hyperscreen, door handles, locks, and the contactors that connect the HV pack. On early X296 software the DC/DC converter did not reliably top up the 12V battery while the vehicle was parked, so cars left standing (or driven only short distances) would go completely dead: no display, no door handle presentation, no READY mode, with the 108 kWh pack sitting at 80%+ charge. Dealers commonly blame infrequent driving before diagnosing the parasitic drain or replacing the battery.

Mercedes' current electronic architecture (shared across the C192 AMG GT, W206 C-Class, X254 GLC, and EQE/EQS) has documented 12V battery drain complaints from control modules not sleeping properly — on the W206/X254 the documented cause is a door control unit keeping the interior CAN bus awake while the car is locked. On the AMG GT specifically, there's no model-specific TSB yet, but the same root cause applies: cars left parked for 1-2+ weeks may need a jump-start, and battery management warnings can appear on the cluster. The W206 has a TSB (LI54.10-P-076820). Typical remedy on AMG GT is a software update at the dealer or, if the battery has been damaged by repeated deep discharge, replacement (~$400-600 for the AGM unit). Most cases are nuisance-level.

On NCV3 Sprinters the heavy charging cable runs from the alternator to the starter stud and then on to the battery, with a fusible link spliced into the harness (the so-called Y-cable). The splice is covered only by heat-shrink that is not truly watertight. Under sustained high-current charging the splice heats up, the shrink tube splits, and road salt and moisture attack the exposed conductor. The link corrodes and its resistance climbs, so the battery never sees full alternator output. Owners report chronic low system voltage, weak cranking, batteries that die early, and alternators condemned and replaced when the cable was the actual fault. Because the fault is resistive rather than open, it often throws no code and voltage measured at the alternator looks fine while voltage at the battery is a volt or more lower.

On both GLA generations, Mercedes has documented cases where the 12V starter battery goes flat while the car is parked. The car then will not start, and on later cars it sometimes will not unlock. In the documented cases, a control module does not go to sleep after the car is switched off. It keeps the car's internal data network (CAN bus) awake, and that runs the battery down while the car sits. First-generation GLA (model series 156): Mercedes bulletins from 2017 name two modules. One is the instrument cluster on cars with sales codes 807/808 built up to September 2017. The other is the HERMES LTE telematics module on US cars with the Audio 20 head unit and code 807 (model year 2017). HERMES software older than 16/45 xx could hold the network awake through the Bluetooth link to the head unit. Second-generation GLA (model series 247): a 2022 bulletin covers cars that cannot be unlocked or will not start and show the dash message "Battery - Start Engine - see Operator's Manual". It says the cause is a module keeping the network awake: the headlamp module, the ambient-light control unit, the instrument cluster, the front SAM, the PTCU or the ESP. The car stores fault U116000, "A bus keepawake control unit has been detected". Not every flat battery has this cause. Mercedes says the network-awake explanation applies only when the car's stored electrical data shows it. If the data does not show it, the battery went flat for a different reason. Mercedes also says a discharged battery does not necessarily need replacing. The bulletins do not point to one part that fails on every 2015-2023 GLA.