Error 15 on Autoterm Air / Planar auxiliary heaters

What does error 15 mean

Error 15 is one of the so-called environmental errors and is not a defect of the heater itself. Just like error 12, it is a problem with the voltage supply, in this case: undervoltage.

When does error 15 occur

The problem usually occurs at startup, when the glow plug starts to heat up. Even if the control panel previously showed a good voltage of 12V, a severe voltage drop can occur at this moment.

Cause

Too little voltage can have many different causes.

As mentioned above, even a relatively new battery that shows a resting voltage of 12V when measured directly between the terminals can be the problem. Resting voltage allows only limited conclusions about how the battery behaves under load, so in this case too the voltage can drop extremely quickly as soon as the heater is switched on.

If the voltage only drops for a very short time, the phenomenon can be difficult to observe with a multimeter. Judging it with a battery monitor is even less feasible. It always displays the average over a certain period of time so that the display doesn't fluctuate constantly.

The voltage drop is therefore not visible, and yet when error 15 is displayed there is almost certainly no fault in the heater itself. Despite 12 V resting voltage and no visible change when the glow plug starts up, the voltage really does collapse and the current is then not sufficient to start the heater.

Besides the battery, the electrical connections can be to blame for the collapsing voltage.

How to fix it

If the battery is ruled out, check for example the fuses and ground connections. Is there good contact where the fuses sit? Sometimes pulling them out and putting them back in works wonders.

Is there perhaps a loose nut on a ground bar or a ground contact to the body?

Another source of error that can cause such problems is cable cross-sections that are too small. Do all cable sizes match the installed devices?

As a small test, you can try to support the system by connecting a battery charger. If the problem persists, the battery can at least be ruled out as the source of the error.

Conclusion

Error 15 is almost certainly a fault in the power supply. If you investigate the causes around the heater, you will most likely find the error there.

Can't find the error?

Unfortunately, it is very difficult for us to assess a system by remote diagnosis and to help find an error that is so far from obvious. If you get stuck, you are of course welcome to get in touch with one of our installation partners and have them help you find the solution directly in your vehicle. You can find a list of installation partners to contact here.