Error 12 on Autoterm Air / Planar auxiliary heaters

What does error 12 mean

Error 12 (or 9 flashes on the PU-5 control panel) indicates a problem with the electrical supply and is the opposite of error 15, namely overvoltage.

Cause

Overvoltage is not that easy to produce on a vehicle electrical system, but it can occur, for example, if the alternator regulator is faulty.

Another cause can be the connection of external chargers with modes such as "desulfation", which use voltage pulses of 16 - 17 volts to counteract the onset of crystal formation in the battery. Many devices cannot tolerate this at all - and that includes the auxiliary heater.

Something similar often happens when very cheap solar charge controllers or inverters are used. Instead of a sine wave, they produce an extremely unclean voltage waveform, which can lead to humming noises or failures in devices. The difference in quality is very easy to see on an oscilloscope..

Fixing the error

Overvoltage on the vehicle electrical system is very rare and unfortunately also hard to measure, especially if it only consists of short voltage spikes.

Our recommendation is to proceed by elimination: first, all connections to the power supply (i.e. the battery), including the alternator, should be disconnected. In the next step, only the heater is connected to the battery and you check whether error 12 still occurs.

Then connect one more device at a time and check again to find out after which connection the error is displayed.

Patience and careful measuring are required here, because the overvoltage is otherwise unfortunately very difficult to locate.

Can't find the error?

If you can't find the problem, you can contact one of our installation partners. That way the installation can be inspected directly in the vehicle. You can find the list of our installation partners here