How to Fix the H94 Error Code on a Webasto Air Top 2000 STC RV Heater

If you have just installed a Webasto Air Top 2000 STC RV heater kit and are now getting ‘error H94’ on your Multi Control HD, don’t worry. This article explains what is required to get your new heater working.

What does ‘error H94’ mean? H94 is a temperature sensor interruption fault code, meaning there is either a short circuit or an open circuit on the temperature sensor or wiring. The heater does not know where to get a temperature reference from. If this fault appears upon initial installation of a new Webasto Air Top 2000 STC, this fault can usually be resolved by doing one of the following:

  1. Installing the terminating resistor
  2. Connecting the external temperature sensor
  3. If H94 still appears, reset the Multi Control HD
  4. Check the main plug is properly installed into the into the ECU

Download the Webasto Air Top 2000 STC RV H94 Error Technical Document

Watch the YouTube video How to fix H94 Temperature Sensor Error on a New Webasto Air Top 2000 STC RV install

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Installing the terminating resistor – recirculated air

The Webasto Air Top 2000 STC RV-specific heater package includes a dedicated RV leisure harness that is more comprehensive than the standard vehicle harness. The RV-specific wiring harness requires either installation of the remote temperature sensor or the terminating resistor, it does not have a resistor taped into the harness like the standard Air Top loom.

Diagram of a temperature sensor and thermostat

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If you are recirculating the heated air within your vehicle, you may decide not to install a remote temperature sensor, in this case, you should install the resistor.

A hand holding a plastic bag with a wire

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The plug-in resistor is installed across the blue/black wires from the heater ECU. This resistor instructs the ECU to monitor the air temperature at the integral sensor, inside the heater casing, therefore relying on the intake air for a temperature reference allowing the heater to determine the power output required to reach your temperature setpoint.

    A diagram of a circuit board

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Installing the remote temperature sensor

If you are drawing fresh air from outside to heat, or heating air from a colder spot in your vehicle (i.e. drawing air to the heater from the cab and heating the living space through a bulkhead), you should install the remote (or external) temperature sensor.

The remote temperature sensor connects to the same blue/black wires on the heater harness as the terminating resistor. This overrides the heater ECU temperature sensor and will accurately measure the ambient air temperature wherever the sensor is installed.

Connected the sensor or resistor and still getting H94, reset the Multi Control HD

It is possible that connecting the sensor or resistor is not acknowledged by the controller until the Multi or Smart Control has been reset.

  1. Go to 'Settings' > Reset
  2. Confirm ‘Yes’
  3. Whilst the screen goes black, press and hold the main button and power button down (for 3 – 5 seconds)
  4. 'Select heater'
  5. Select the correct heater type “Air Top 2000 STC”

 

How to reset the Webasto multi control hd in the workshop menu How to select the correct Webasto heater on the Multi Control

This reset procedure can take a few attempts, the on/off button and the control knob button must be held down whilst the screen is blank.

Once the correct heater version is selected the heater and controller will go through its initial start-up procedure and check for a connection to the external temperature sensor.

The main plug for the heater is not fully pushed into the ECU

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 w-bus, H08 fuel pump short circuit, 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.

If you are still experiencing issues with this fault code and require additional support with your heating system, please submit a support request or contact us directly.