Everyone in my wifes family drives a VW Passat with 2 l diesel. They all have Webasto engine heaters for the winter. My wife has the oldest Passat and her heater remote broke, so we started to think about activating the heating by mobile phone.

One idea was to use an Arduino with GSM shield. That way we could get other functionalities also, like one button garage door opener (it works by calling to the garage door) and temperature + position logging. Then Marko found the RTU5024 module.

RTU5024 GSM garage door opener is a super simple device. You give it a SIM-card and 12V and it starts to work. The only thing it does is to activate a relay for a pre-programmed time when an allowed number calls it. The relay is connected to the Webasto clock units "flame" button. It simuates a push of the button.

Step 1: Power Consumption

To be able to use the remote function, the RTU module needs to have power 24/7. Because it is in a car the power consumption is a big issue. According to the datasheet the maximum current draw is 25 mA. With a 100 Ah battery this means 167 days or almost a half year of standby. Good enough!

I also plotted the current draw with my Mooshimeter. Please have a look at the trend in the pictures. The current draw during standby is actaully only half from what the datasheet said at 14 mA! When calling the device there is a 80 mA current peak from the activation of the relay. I called it 4 times in a row and found out that the current rises for every call. It is not normal to call many times so this is not an issue, but good to know.

Step 2: Configuring the RTU Module

Before installing the module in the car it is a good idea to configure it first. It is much nicer to do it at home rather than in a cold car. The configuration is done by sending SMS messages to the device. It responds with a confirmation message. Every command consists of: password + command + parameter + #. Default password is 1234. In the manual these commands are well documented. Please look there for deeper instructions.

I sent these commands:

1234TELxxxxxxxxx#
- You need to first tell the device its own telephone number. If country code is +358 and number 0401234567, then you send the command: 1234TEL00358401234567#
1234A001#00358408901234#
- My telephone number (+358408901234) is in memory space 001 and it can operate the relay at any time
1234A002#00358405678901#
- My wifes number is in memory space 002 and it can operate the device at any time
1234GOT001#
- The relay will be activated 1 second for each call. 001 means 1 second. Maximum is 999 = 17 minutes
1234AUT#
- Only authorized numbers can activate the relay. In this case my wife and me (memory space 001 and 002)
1234GON##
- By default the device sends a message every time the relay goes ON or OFF. With this message you turn off the "relay ON" message
1234GOFF##
- This turns off the "realy OFF" message

Perfect! Now the device is working as we want. It allows only my wife and me to activate the relay. Relay stays on for 1 second and it does not send confirmation messages.

UPDATE 14.1.2021 Iphone problems

Suddenly my wifes Iphone did not work anymore with the RTU module. When she called, Webasto stayed off. We found out that for some reason her Iphone makes a second call automatically probably because the first call fails so fast (RTU pushes the red button as soon as you call it). So first Iphone calls, RTU denies the call and starts the relay. Then Iphone calls automatically a second time. What this does is that RTU pushes two times on the flame button on Webasto. So it turns it on and then back off.

If you have an Iphone and you experience problems you have two choices:

1. When calling the device, you need to cut the call manually, maybe even before you hear that RU has answered

2. Use SMS to start the device. By sending code 1234CC the device opens and closes the relay according to the set schedule.

The RTU module has worked like a charm all these years. I really recommend this device if you need to have a remote relay somewhere.

Step 3: Connecting RTU5024 Relay to Webasto

The idea is to simulate a press of the "flame" button on the Webasto clock. This starts the heating for a set amount of minutes (30 min by default). It is the button in the bottom left corner. This is done by connecting the relay NO and COM in parallel with the button.
On the back side of the clock are many test points. You need to find a ground point and the point where the button is connected. Please see attached photo with red rings around the points. After soldering the wires in place I put quick epoxy on the cables and solder points to keep them sturdy in place. Remember that the installation is in a car with a lot of vibrations.

To finalizy the installation a small hole needed to be drilled to the back plate for the new wires. I also removed some of the plastic so that the wires will fit nicely in the case. Also the hole in cars dashboard needed to be enlarged a bit for the new wires.

Step 4: Supplying Power to RTU5024

As said before the GSM module needs 24/7 power. In older cars this is an easy task: just take power from the cigaret lighter socket. But on newer cars the socket turns off with the car.

There are some possibilities to power the module:

Use a lipo mobile phone charger + 12V step-up module to power RTU when car is off. Cigaret lighter will charge the lipo battery when driving

Use a OBDII cable and the 12V output pins to power RTU5024. OBDII port 12V output is specified to be able to supply at least 4 A current which is more than enough for this project

Use the Webasto clock power lines. I used this one

Because this is supposed to be a permanent installation I did not want to occupy the OBDII port or the cigaret lighter socket. When using these there is always the possibility that someone disconnects the conneector and then the remote does not work.

Using the Webasto power lines

First you need to figure out which pins give 12V. In this case it was the red/black and brown wires. Red/black is +12V and brown is ground. See attached picture. The "relay" pins start the Webasto when shorted and stops it when connection breaks.

I did not want to cut the original wires so I used an exacto knife to scrape off the insulation and then soldered long enough wires for RTU5024. I insulated the solder spots with electrical tape. This is not the best solution but should work.

It is highly adviseable to put a fuse between the RTU module and Webasto clock! They do not cost much but can save a lot of nerves and possibly avoid a broken clock. I used a 1A glass fuse connected to the +12 V line. You can see the black holder in one of the pictures.

Step 5: Finalizing Installation

The last thing to do is to connect wires to the GSM module and hide it somewhere. There is a handy compartment under the steering wheel which fitted the module perfectly. Now it is easy to get to when needed. Downside is that you can´t use the compartment for anything else.

Another possibility would have been to hide it under the screwed panel between the pedals and compartment. As the human is a lazy creature, the decision was extremely easy: compartment!

After this a test call revealed that the installation was a success! Webasto starts when calling to the module. If there is a need to stop heating in the middle, another call will stop the module.

Step 6: Final Thoughts

This project was useful, easy to implement and cheap. You can buy the GSM module for 20 dollars from China. Other stuff needed is a fuse holder and some cables. If a "professional" would do this, it would cost hundreds of money...

I highly recommend this modification to any Webasto owners. Think about the possibilities: you can be in Australia and start your Webasto in Finland ;)

The pictures are the rest I did not find a place in the steps. Maybe they help someone.

A couple of words about the RTU5024 module. Usually when buying Chinese stuff, the quality is exactly what you pay for = bad. But this module feels and seems like a well thought product. The device is well made, PCB looks good, manual tells you everything needed and the device itself has only the features you need. Not tons of extra s*it which looks good in the datasheet but you never need to use.