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Discussion Starter · #1 · (Edited)
Hey Guys,

I have a 2013 CT200h with a horn issue. It started as an intermittent issue and now it is not working at all.
In my attempts to diagnose and fix the problem, so far I've bumped into more problems trying to understand the wiring related to
the horn system. I thought it would be a good idea to list them numbered as below.

1)Under the bonnet fusebox is a one confusing box. There are two things that are marked as the fuse and the relay for the horn on the fusebox cover but
it makes no sense as the there in no fuse or relay where it points out but a vacant lot.
2)I looked into the fusebox inside the car, but there is no fuse or relay in there that is designated to the horn either.
3)I removed both the high frequency and low frequency horns to bench test them, however it is not possible to bench test them with a 12v car battery.
The horns simply make a 'tin' noise when I connect the battery to them. But, the horns are good because they both work fine with the security alarm when I trigger the alarm.(For that reason I ruled out any issues with the horns themselves).
4)I hear no click from anywhere from the front of the vehicle(horn relay) when the horn is pressed(relay clicking noise)
5)I can't see any error indicator lights on the dash.

I have a bunch of questions. If any member in the forum can help me with these, I will be really grateful.

1)Where is the fuse and the relay for the horn? Is it the main integration relay under the fuse box? Disconnecting that relay means disconnecting the battery as well, is it not?
2)What is the reason for the horns to not make the horn sound when they are bench tested?
3)Has anybody else experienced this problem and tried to diagnose the problem and ended up with similar problems like me above?

I've read a thread here that said the OP's horn issue was from the faulty clock spring assembly.
I would like to rule out other issues before I would go to the length of taking off the steering wheel assembly, as it is quite a big job.
Removing the steering wheel assembly(air bag and clock spring) means disconnecting the main integration relay and disconnecting the battery(according to the CT200h repair manual) and that means having to calibrate lot of electronic parts(sensors, etc) according to the repair manual, and I would rather not go there and instead prefer to wire up an entirely new horn with a new horn switch on the dash, new relay and a new horn under the bonnet.

Any help will be greatly appreciated. I can post some pictures tomorrow.

Thanks in advance.
 

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Hi. Did you get a response to this as I have exactly the same issue. Like you I find it very strange that the slot for a 10A fuse specifically labelled as the horn is empty, I took one of the spares and fitted it into the this empty slot with no effect.
I think (and hope) that its not the Clock Spring as on my car all of the other functions such as radio, phone and display selection all work from the steering wheel controls. From my internet reading this is a common issue with these cars and as the horn is a mandatory safety feature you would expect Lexus to be all over this.
I also would welcome any advice.
 

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I found my problem. The CT200h is especially popular in the UK with catalytic converter thieves at the moment. I checked out another forum and found out that they cut the horn cable to silence the alarm. I lost my cat at about the same time as my horn stopped working without making the mental connection. Sure enough, that was the problem - so you were right it was a voltage drop. Very relieved as the a clock spring replacement is very expensive. Thanks again!
 

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I found my problem. The CT200h is especially popular in the UK with catalytic converter thieves at the moment. I checked out another forum and found out that they cut the horn cable to silence the alarm. I lost my cat at about the same time as my horn stopped working without making the mental connection. Sure enough, that was the problem - so you were right it was a voltage drop. Very relieved as the a clock spring replacement is very expensive. Thanks again!
No worries. Glad it wasn't the spring.
 
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