After a rainy season my Han started behaving strangely in a way that tracked the weather. Door handles stuck. The car reported a door not closed when it was shut tight. Cruise control stopped working. Interior lights stayed on. At one point the system believed I was pressing the brake and the accelerator simultaneously, and the brake lights stayed on until everything dried out.
Every one of those cleared up as the car dried. That pattern is the useful part: if faults come and go with the weather, you are probably looking for water and connectors rather than for the components that are throwing the errors.
What happened, in order
The rainy season arrived and the door handles started sticking.
One handle was replaced. After that the car began showing a “door not closed” message with the door shut tight. Then cruise control stopped working. The interior lights stayed on. And once, memorably, the car decided I was pressing the brake and the accelerator at the same time, and the brake lights stayed on until everything dried out.
Here are two of those on the dash together, because a description of this reads as exaggeration until you see it:
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Not a single one of those is a door handle fault. They are all things downstream of a door handle, on the same electrical neighbourhood.
Why a door handle takes cruise control with it
I am not an automotive electrician and I am not going to pretend to diagnose this properly. What I can say is what the pattern suggests, and it is the same thing any experienced person will tell you: when unrelated systems fail together and recover together, look for something common to all of them.
On this car my working assumption is corroded connectors. That is an assumption rather than a diagnosis, and I want to be clear about which it is. Nobody has shown me a corroded connector. What I have is a set of faults that appeared with water, moved around, and disappeared when the car dried.
The reason it is worth writing down anyway: a service centre presented with “cruise control has failed” can spend a long time on cruise control. Presented with “five unrelated things fail when it rains and recover when it dries”, the conversation should go somewhere different.
Water in the cabin
Separately, about a year ago I found water getting into the cabin.
I fixed the leak myself in the end. The service centre had not found it, and I had pointed it out to them.
I am deliberately not claiming a connection between the leak and the electrical faults, and I have not claimed one anywhere else either. I do not have the evidence for it. What I will say is that if you have water entering a cabin and electrical faults that follow the weather, treating them as two unrelated tickets seems optimistic.
What I would do differently
If your car develops odd electrical behaviour, write down two things every time: the symptom, and the weather.
That sounds trivial. It is the single most useful thing I did, because after a few entries the pattern was obvious, and a pattern is far harder to dismiss than a complaint. “The cruise control is playing up” invites a shrug. “These five systems fail when it is wet and recover when it is dry, here are the dates” is a different conversation.
Photograph anything visible before anyone touches it. And if you can, check the obvious water paths yourself. I found my leak, which is not a boast: it means it was findable.
The part that still sits badly
The handle that started all this went in working. It came back replaced, and the faults followed.
I have written up that sequence properly in the post about the 12V battery, because the same visit is where the battery ended up flat and where the workshop spent weeks on something an owners’ group answered in a minute.
Five years and 50,000 km, and the car still drives beautifully in the dry. That is what makes this frustrating rather than simply disappointing.
Has anyone else had weather-tracking electrical faults on a Han? Specifically: did anyone get a proper diagnosis rather than a part swap? I would like to know it is possible.
FAQ
Can rain cause electrical faults on a BYD Han?
On mine it did. After a wet season the car reported a door not closed while shut, cruise control stopped working, interior lights stayed on, and once the system read the brake and accelerator as pressed together with the brake lights staying on until things dried out.
Do the faults go away when the car dries?
In my case yes, which is the most useful diagnostic clue available. Faults that appear with water and clear as it dries point at moisture and connectors rather than at the individual components reporting errors.
What causes it?
My working assumption is corroded connectors, and I want to be clear that it is an assumption. Nobody has shown me a corroded connector; what I have is a set of unrelated systems failing and recovering together with the weather.
My BYD says a door is not closed when it is closed. What should I check?
On my car that message appeared after a rear door handle was replaced, alongside other electrical faults, and it tracked the weather. Worth recording when it happens and in what conditions before assuming the door sensor itself is at fault.
Does water get into the cabin on a BYD Han?
It did on mine, found about a year ago. I traced and fixed the leak myself after the service centre did not find it, though I am not claiming that leak caused the electrical faults.
What should I tell the service centre?
Bring a log rather than a symptom. Record each fault with the date and the weather. A list showing several unrelated systems failing when wet and recovering when dry is much harder to answer with a single part swap.
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