The T12 error fault code on a Webasto Multi Control HD is a common error message. In this article, we highlight the most common causes and how to fix them.
What does 'error T12' mean? T12 is a communication fault code indicating the controller cannot see the heater unit. This error message could be displayed as a result of any one of the following:
- Check you have the correct Multi Control version for your heater
- The Multi Control is connected to the wrong plug on the main harness
- There is no power at the heater unit; a blown fuse
- Automatic heater detection did not work, select the correct heater
- The main plug for the heater is not fully pushed into the ECU (Air Top 2000 STC)
Download the Webasto T12 Error Technical Document
Watch the You Tube video How to fix Webasto T12 Multi Control error fault code - 5 steps
This article is suitable for:
- Webasto Smart Control and Multi Control HD timers
- Webasto Air Top 2000 STC, Air Top Evo 40, and Air Top Evo 55 air heater models (controller versions: 90300026D, 9030025A, 9030910E)
- Webasto Thermo Top C, Thermo Top Evo, Thermo 90 90S 90 ST, and Thermo Pro 90 water heater models (controller versions: 9030026D, 9030025A, 9030911D)
- New heater installation or controller upgrades on an existing install
Firstly, check you have the correct controller for your heater.
Before you delve into the Webasto controller setting and wiring configuration a good initial check would be to make sure the part number of the controller you have is correct for the heater type you intend to use the controller on. The suffix on the part number does not influence compatibility but the numbers are important.
- For Webasto Air Top heater models: 9030025D (old version), 9030910E
- For Webasto Thermo Top heater models: 9030025D, 9030911D
The Multi Control is connected to the incorrect plug.
This is usually an issue when connecting the Multi Control for the first time, either during a new installation or when upgrading the controller from a rotary rheostat controller on an existing air heater installation.
The Rotary dial controller uses a different four-pin plug for switching. The 'potentiometer' plug (X9a) is not suitable for the Multi Control and connecting to this cable will cause a T12 fault.
How to fix: Connect the Multi Control to the X9c plug labelled "TELESTART, THERMOCALL, DIAGNOSE". This connection uses a W-Bus (yellow) wire for heater switching and temperature control.
See the technical page - Webasto Controller Connection Air Top 2000 STC EVO 40 55 Wiring Manual
There is no power at the heater unit; have you got a blown fuse?
An indication this could be the issue is that the heater started to work, once. If this is a new heater installation and the 1 amp controller fuse has been installed into fuse position 1 (F1), as soon as the heater glow pin activates this fuse will blow, resulting in loss of power at the heater and "Error T12" on the controller.
How to fix: Check fuse positions 1 and 2, and reinstall the fuses in the correct positions.
- F1 is power to the heater, 20A (12V), 15A (24V)
- F2 is power to the controller, 1A
Automatic heater detection did not work, how to select the correct heater manually.
Everything is connected correctly, fuses ok, but no response from the heater, and then "T12"? There could still be a lack of communication if the controller has not successfully identified the correct heater model.
To manually select the correct heater type you need to follow the steps below:
- Go to 'Settings' > Reset
- Confirm ‘Yes’
- Whilst the screen goes black, press and hold the main button and power button down (for 3 – 5 seconds)
- 'Select heater'
- Select the correct heater type i.e. “Air Top 2000 STC”
This reset procedure can take a few attempts, on/off button and the control knob button must be held down whilst the screen is blank and the screen does not stay blank for very long.
Once the correct heater version is selected the controller will be able to communicate with the heater.
The main plug for the heater is not fully pushed into the ECU.
This issue is most common on the Webasto Air Top 2000 STC. When the main heater plug is not fully home into the ECU it is possible to get spurious fault codes, amongst those; T12 - no communication and H94 - temperature sensor open circuit.
To be sure that you have inserted the main heater plug correctly, remove the plug, and reinstall. When you reinsert the main plug you must hear or feel the locking tab 'click' into place.
See Butler Technik technical document for further guidance: Webasto Air Top 2000 STC Electrical Plug Connection to ECU
For more technical information and downloads on the Webasto Multi Control HD see our technical library page: Webasto MultiControl HD and Smart Control Manuals | Butler Technik
Please contact us if you require any further support with your Webasto heater or controller.
