P0C79: Drive Motor A Inverter Voltage Too High
What to do
Expect electric drive to cut abruptly rather than fade — that is protection working, not a second fault. If it happened on a long descent or with a nearly full battery, say so, because that points at regeneration having nowhere to go rather than at a hardware failure. Otherwise this belongs with the contactor and pack codes, and it should not be cleared and ignored: the condition it protects against damages the inverter.
What this code means
The DC link voltage at drive motor A's inverter has exceeded its limit.
The DC link is the pair of heavy rails inside the inverter that everything else hangs off, and it normally sits at whatever the traction pack's voltage is, because it is connected to it. So for it to rise above the pack, something must be pushing energy into it faster than the pack is taking it away.
An electric machine does that whenever it is turning and not being driven — it becomes a generator. Which sets up the failure that makes this code urgent rather than merely noted: if the contactors open while the motor is still spinning, the energy the machine is producing has nowhere to go. The pack is disconnected, the link capacitors are all that is left to absorb it, and the voltage climbs very quickly toward the point where the switching devices fail. Modern designs have protections for exactly this, and this code is one of them announcing itself.
The gentler readings are a full pack with regeneration still being commanded — the P0C30 situation — or a measurement fault. But the response is a hard cut to electric drive rather than a derate, and that is deliberate: it is faster to stop asking the machine for anything than to reason about why the voltage is rising.
Likely causes
Start here
- Faulty battery contactor · specialist
- Faulty power inverter · specialist
Less common
- Charging system overvoltage · specialist
- Corroded or loose connector · specialist
- Weak or failed cell group in the battery pack · specialist
Symptoms
Components involved
Information, not instruction
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Community experience
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