Model
Mercedes-Benz S-Class
Workshop cases
Diagnostics in real cases.
Symptoms, measurements, the established cause and the result of the work carried out.
№ 3Mercedes-Benz S-Class W223 — no connection between MBUX and the rear tablet due to incompatible software versions
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Mercedes-Benz S-Class W223 — no connection between MBUX and the rear tablet due to incompatible software versions
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Generation / year
W223
System
MBUX multimedia system: head unit and rear-seat entertainment system
Symptoms
The rear entertainment tablet could not connect to the vehicle’s MBUX system, leaving the corresponding functions unavailable. Inspection showed that the tablet had received an automatic software update while the MBUX head unit was still running an older version. The difference in software versions disrupted communication between MBUX and the rear tablet.
Fault codes and measurements
XENTRY Diagnosis was used to check MBUX and the installed software versions. A newer software version was available for the MBUX head unit; XENTRY estimated approximately three hours for the programming procedure. During preparation, XENTRY also listed additional symptoms addressed by this update: issues with Apple CarPlay, Android Auto and Bluetooth Audio Streaming; navigation and vehicle-positioning inaccuracies; map-display errors; problems with the image and individual display elements; missing menu items; issues with internet services and data media; and other multimedia-system malfunctions. These additional symptoms were not the complaint for this vehicle; they were among the issues the new software version was designed to resolve.
Established cause
The rear tablet could not connect because the software versions of the two systems were incompatible. After the tablet’s automatic update, its software was no longer compatible with the older version installed in the MBUX head unit.
Repair performed
The MBUX head unit was programmed and its software updated using Mercedes-Benz XENTRY Diagnosis. Communication between MBUX and the rear tablet was checked again after programming.
Result
After updating MBUX, the software versions were compatible again. The connection to the rear tablet was restored and the rear-seat entertainment system operated correctly.
№ 2Mercedes-Benz S 500 W222 — charging above 16 V caused by a faulty alternator regulator
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Mercedes-Benz S 500 W222 — charging above 16 V caused by a faulty alternator regulator
Model
Mercedes-Benz S 500
Generation / year
W222 / 2014
System
Charging system: alternator, voltage regulator and alternator control line
Symptoms
The battery warning lamp was illuminated, with a diagnostic fault indicating excessive battery internal resistance. Charging voltage was initially within the normal operating range after starting, then intermittently rose above 16 V.
Fault codes and measurements
Stored fault B14F4500: starter battery resistance too high. Charging voltage initially remained normal, then intermittently exceeded 16 V. The alternator control line was measured with an oscilloscope and a LIN waveform was recorded. The measurements identified incorrect voltage-regulator operation as the cause, rather than the battery.
Established cause
The alternator voltage regulator was faulty, causing intermittent overcharging. The incorrect charging voltage led to a misleading fault for excessive battery internal resistance.
Repair performed
The alternator was removed and repaired. The regulator fault was rectified and the alternator refitted. The charging system was then checked under different operating conditions and electrical loads.
Result
Charging voltage returned to its normal operating range. Intermittent charging above 16 V was eliminated, the battery warning lamp no longer appeared and the charging system operated correctly.
№ 1Corroded rear radar sensors disrupt CAN communication and automatic headlight control
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Corroded rear radar sensors disrupt CAN communication and automatic headlight control
Model
Mercedes-Benz E 350 CDI
Generation / year
W212 / 2012
System
CAN communication network: multifunction camera, front SAM, headlight control units, instrument cluster and rear radar sensors
Symptoms
Automatic headlight control and switching did not work and a warning appeared in the instrument cluster. Diagnosis revealed disrupted communication between the multifunction camera, central gateway, both front headlight control units and instrument cluster.
Fault codes and measurements
Active and stored faults: U103788 — front CAN communication impaired, bus off; U103712 — front CAN communication impaired, short to positive; C14687 — communication disrupted between multifunction camera and central gateway; C14682 — invalid CAN message from central gateway N93 to multifunction camera; U118A00 — communication disrupted with left headlight range control unit; U118B00 — communication disrupted with right headlight range control unit. CAN High and CAN Low were measured at the front SAM connector towards the left headlight. Before ignition, both signals were normal. With ignition on, line voltages rose well outside the permitted range and network communication failed. The measurements confirmed a short to positive supply in the CAN network.
Established cause
Sequential checks found the camera, front SAM, headlight control units and wiring functioning correctly. Tracing the network topology showed that the rear radar sensors were on the same CAN network. Both sensors in the rear bumper were heavily corroded. With ignition on, their internal fault caused a short to positive supply and excessive CAN line voltage, producing apparent faults in the camera, front lights, SAM and cluster.
Repair performed
Both heavily corroded rear radar sensors were disconnected and isolated from the CAN network to confirm and remove the cause of the communication failure. Diagnosis and oscilloscope checks of CAN High and CAN Low were repeated. The customer was informed that the faulty sensors required replacement and chose to have them replaced later.
Result
After isolation of the faulty sensors, CAN High and CAN Low voltage and waveforms returned to normal. Communication between the camera, gateway, front SAM, headlight control units and cluster was restored, and automatic lighting worked again. Functions that depend on the rear radar sensors remain unavailable until the sensors are replaced.