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OBD Fuse Removed - Is this the expected behaviour?


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I bought a 2020 ST Line 125bhp Fiesta a couple of weeks ago and I'm really enjoying it. I learned it has the new chain driven cam engine without mHEV which I'm pleased about too. The last Ford I owned was a 2 litre petrol 1999 Focus Zetec which was a fantastic car and I kept it for 15 years.

I wanted to improve security a bit on my Fiesta as I understand the OBD port is a weakness. I have removed the "data link connector" fuse from under the glovebox.

Before I did this, I plugged in a code reader into the port and connected to it and it confirmed zero errors. After removing the fuse, the code reader powered up but could not connect. When I started the engine, the code reader connected successfully and confirmed zero errors again.

Is this the expected behaviour for after pulling the fuse?

Also, any other security tips you guys would recommend?



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Was it fuse F10 that you removed ?

The OBDII port is just a fancy terminal block with multiple connections to the vehicles many systems. Removing the fuse for the power to it does nothing except prevent anything plugged in to the socket from using the vehicles own 12volt system to power the external device. Removing the fuse in noway prevents connection to the vehicles Canbus or other systems.

Personally I recommend the fitment of a tracker with the option of remote disablement in the event of theft. Professionally installed it costs £265 and then £6 per month for the tracking service. You can spend many hundreds for alarms systems, immobilisers and the likes but none of them are much good if the vehicle is picked up, or towed away.


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29 minutes ago, Aldridge Andy said:

I thought in the Mk8 if the alarm is triggered the OBDII Port shuts down?

You can't shut down what is only a socket. It's not a module or other kind of electronic device, it is simply a series of wires from different modules or devices brought together on a common socket to enable a convenient way for diagnostic equipment to be quickly and easily connected to the vehicle.

You could install a two pole hidden relay and interrupt the Can Hi and the Can Low signal wires to the OBDII port but it would have to be a good quality signal relay (typically Gold flashed contacts) to ensure that there would be no corruption of the Can signal to the port when it is needed. 

As an alternative you could have a hidden switch in the supply lead(s) to the Gateway Module which would stop most communication but I suspect that may bring with it it's own problems.


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18 hours ago, unofix said:

Was it fuse F10 that you removed ?

Yes, F10 was the one. There still seems to be power to the port though as my cheap OBD code reader still powers on when I plug it in, just unable to establish communication.

I have considered a tracker but have read they can be defeated with a £10 GPS blocker.


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