BMW E39 Webasto does not start or shuts off in freezing weather
Why does the E39 Webasto not start or shut off in hard frost?
The Webasto shuts off when the voltage drops too low, and the limit rises as it gets colder. Heating therefore ends long before the battery is empty. A weak battery or voltage loss in the wiring makes it worse. The limit cannot be changed.
How do I find out whether voltage is the cause?
Measure the voltage at the Webasto connector while it is heating and compare it with the battery terminals. If the difference is more than one volt, the fault is often in the battery power cable or in a corroded spot in the positive lead. Replacing the wiring has fixed the problem.
What can I do to make the Webasto work better in frost?
Keep the battery full and in good condition. A lower interior blower speed loads the battery less: the blower clearly increases current consumption. A charger intended for permanent installation, e.g. a CTEK, helps, but with a weak battery it may not be enough.
What else can shut the Webasto off after a couple of minutes?
If the fuel pump clicks but the Webasto shuts off soon after, the cause can be overheating when the water pump does not circulate the coolant. Coolant above 65 °C also prevents heating.