Workshop support: The smart EQ is no longer charging, what now? (feat. defective DCDC converter & blown fuse)

There are two known error messages when the smart EQ no longer wants to take a charge. Some of the most clicked FAQ questions in the smart EMOTION Wiki:

What can I do about "Charging not possible - Visit workshop"?

What can I do about "Malfunction - Visit Workshop"?

In terms of content, they do not differ and ultimately it is purely a coincidence which of the two messages the smart chooses. But the result is that you have to unplug it, lock it and wait 15 minutes. So all control unites fall asleep and restart after 15 minutes. In 95% of cases, this solves the problem and makes the trip to the workshop unnecessary. This won't find anything and won't be able to fix anything. It was just one of the installed Renault control units which simply hung up and the Zoe genes in the smart showed up.

Statistically speaking, the error occurs every 30,000 km, sometimes more often, sometimes less often. If it does increase and occurs less than every 10,000 km, replacing the 12 V battery can help. There is more about this in the smart EMOTION Wiki: How do I replace the 12V battery? [ED4]

What to do if letting the smart fall asleep doesn't solve the issue?

If letting it fall asleep no longer helps, the next question is whether the smart still is able to drive. Yes, the HV battery is probably already relatively empty, which is why you want to charge it. But still: Does it still drive under its own power?

If the smart still wants to drive under its own power, definitely nothing has to be for for a mid-4-digit sum. Although the motor and the entire drive train are part of the 22 kW charger, if the smart is still driving, everything is fine. Otherwise it wouldn't drive anymore. It is then very likely that the fuses in the cable harness from the type 2 socket to the drive train have blown. This can happen if the wallbox used is not properly grounded or there are other problems with the wallbox. The type 2 socket and the cable set must then be replaced, as the fuses are pressed into the cable harness and cannot be replaced individually.

If you first want to measure whether it is really your fault, you can remove the rear right wheel arch liner, open the cover there and measure the fuses.

Alles rund ums Reparieren eines elektrischen smart EQ

There are other fuses in the drive train, these can also be checked. Since these are usually not responsible for the smart no longer charging, I won't go into them here. More about fuses in my general article: Everything about repairing an electric smart EQ

If the smart no longer wants to drive under its own power, then it is quite possible that the DCDC converter is defective. Its job is to charge the 12 V battery. Aside from the 400 V system that operates the motor, heating and air conditioning, there is also a 12 V system. This supplies the radio, heated seats, lights and all control devices. If its voltage is too low, it can no longer close the HV contactors of the HV battery. Or in other words: It can no longer “start” the HV battery. Then the smart won't drive anymore.

It's quite easy to test whether the DCDC converter is still working: Measure the 12 V voltage with the multimeter while the smart is switched on and set to "Ready". Then the 12 V voltage should be over 13 V with the DCDC converter working. If you are not completely sure, you can switch it off again for comparison and check whether the measured voltage changes. If the 12 V voltage does not change when switched off, it is defective.

Basically, the DCDC converter is always active when the smart is on "Ready" or is currently charging actively on the wallbox.

If the smart still has a warranty and Mercedes covers all the costs, then let them replace half the drive train for a lot of money. But if it's a matter of you covering these costs yourself, just replace the DCDC converter.

Unfortunately, this is not available individually as a spare part from Mercedes. But you can get it directly from Renault and then code it on the smart. I also have it already coded available upon request.

Toto replace it, you have to lower the rear axle with the entire drive train to get to the cover behind which it is hidden (2).

Alles rund ums Reparieren eines elektrischen smart EQ

After the replacement, the rear axle must be properly screwed back into the car and, ideally, the track must also be adjusted again.


In general, it is a bit unfortunate that the Mercedes dealers cannot really handle the smart EQ in this special case and they have to be shown how to diagnose errors. But with the help provided here, both dealers and end users should be able to easily check for themselves what is defective and then get it repaired for less than half of the originally estimated amount.

In both cases, the spare parts cost somewhere around €1,500 and with installation they cost less than €2,500.

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