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Jaguar S-Type Aux Heater / Webasto Thermo Top V Part 2 – W-Bus Diagnostics

As I mentioned in the previous post, these heaters have a standard interface that’s used for control & diagnostics, the W-Bus. This is transmitted over the K-Line of the vehicle bus, and all heaters, regardless of firmware modifications done by the various car manufacturers respond to this interface. Official Webasto diagnostic adaptors are available, but these are just a very expensive serial adaptor. A much cheaper option is a ~£5 Universal ODB adaptor.

ODB2
ODB2

Above shows the signals on the ODB connector – the ones we’re interested in here are Pin 16, the +12v supply, and Pin 7, K-Line. Connect Pin 16 to the positive supply to the heater, and Pin 7 to Pin 2 on the Webasto heater. (Valid for all TT-V heaters).

Device Selection
Device Selection

Once these two connections are made to the heater, fire up the Thermo Test software. The screen above will be displayed. Pick W-Bus at top left.

COM Port Selection
COM Port Selection

First thing, connect the ODB adaptor to USB, and change to the correct COM port in Thermo Test. There may be several in the list, but a newly connected USB device should show up with the highest COM number.

Thermo Test
Thermo Test

Once Thermo Test is running, start communications by going to the Diagnosis Menu > Start Diagnostic (F2 keyboard shortcut).

Initialized
Initialized

After a few seconds, communication will be established. This will show faults, if any are present, and allow testing of the heater & it’s component parts. A summary report can be generated with Diagnosis > View Summary:

This shows all the important stuff, including running hours. (5388Hrs on this heater!). Most importantly, there are no faults listed.

Heater Running
Heater Running

The heater can be fully tested by issuing a start command from the Command Menu > Parking Heating option. Obviously cooling water will be required for this, along with an external water pump. (The water pump control output on these heaters seems to be totally disabled in firmware, as they rely on the engine’s coolant pump). I used a bucket of water along with a small centrifugal pump to provide the cooling. During this test I noted that the firmware is much more aggressive in these units. The marine versions shut down at ~72°C water temperature, whereas these don’t so the same until ~90°C.

Now I’ve managed to communicate with the heater, I’ll get onto building a standalone controller so I can dispense with the Windows VM for control.