Kia Owners Club Forum banner

1 - 6 of 6 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter · #1 ·
Hello,
So I bought my Kia Cee’d ls back in July, with a couple of problems including a faulty battery, which I was unaware of when I bought it. A couple days later I was planning on taking my other half away on a special night, where I was planning to propose, however my car decided on that day to die on me! In a blind panic I tried jump starting the car, but as the terminals weren’t colour coded and the signs were worn, along with the anxiety of missing my chance to propose, I but the jumper leads on the wrong way and fried my car.
The car has been serviced, MOT’d and has had various work done on it since, but nobody has been able to find the fault with the aircon. The fuse blows instantly when the key is turned, so there must be a short somewhere, but the fuse box is fine, and the fan, sensors, wiring etc seem fine.
A couple of other electrical issues I noticed which might be linked are that the front wipers only work on certain settings, the back wiper doesn’t work, the AC controls on the dashboard have no power and the usb socket causes a separate fuse to blow. I have no clue whether any of it is linked, but if I can’t fix this car myself then I’d be sad to say goodbye, as it’s a really nice car to drive and it has served my family and I well.
 

·
Registered
Joined
·
552 Posts
Someone else connected the Battery round the wrong way.
Popped all sorts. Got it sorted in the end.
Likely the Diode in the Blower Relay

 

·
Registered
Joined
·
5,229 Posts
Every relay has a diode connected across the coil ("quench diode" in English "snubber diode " in American, and "flyback diode" is also used but this is imprecise). These diodes are there to dissipate the large reverse voltage a relay coil generates when it is de-energised, protecting the electronics.

Connecting a battery with reverse polarity will cause a large current to flow in these diodes, blowing fuses and destroying the diodes too. Usually these diodes will fail open circuit so you don't really notice any problem (however they are no longer quenching and this will add cumulative damage to the ECU drivers). Rarely an affected diode will fail to short circuit and this will repeatedly blow fuses. Exactly which diodes fail open, fail short, or survive the experience is likely to be random.

Look for relays being supplied by the failing fuses and test the diodes within. The diodes themselves are very cheap and readily available (usually 1n4004S - the S is important) but need the relay housing to be opened and soldering to fit. If you go for this note which way round the diode is fitted becore you remove the old one as the replacement must be fitted the same way round.

There will be other diodes which have failed open but will, for now at least, give no issues but the electronics driving those relays are at risk.

I assisted with the previous case mentioned and it was indeed the blower motor relay quench diode - could be the same or another or more than one in your case.

Unless you test and replace all failed (short or open) relay diodes that car is just building up expensive problems.

Don't think this is the USB issue though but it might explain the others (multiple faults).
 

·
Registered
Joined
·
2 Posts
Discussion Starter · #5 ·
Every relay has a diode connected across the coil ("quench diode" in English "snubber diode " in American, and "flyback diode" is also used but this is imprecise). These diodes are there to dissipate the large reverse voltage a relay coil generates when it is de-energised, protecting the electronics.

Connecting a battery with reverse polarity will cause a large current to flow in these diodes, blowing fuses and destroying the diodes too. Usually these diodes will fail open circuit so you don't really notice any problem (however they are no longer quenching and this will add cumulative damage to the ECU drivers). Rarely an affected diode will fail to short circuit and this will repeatedly blow fuses. Exactly which diodes fail open, fail short, or survive the experience is likely to be random.

Look for relays being supplied by the failing fuses and test the diodes within. The diodes themselves are very cheap and readily available (usually 1n4004S - the S is important) but need the relay housing to be opened and soldering to fit. If you go for this note which way round the diode is fitted becore you remove the old one as the replacement must be fitted the same way round.

There will be other diodes which have failed open but will, for now at least, give no issues but the electronics driving those relays are at risk.

I assisted with the previous case mentioned and it was indeed the blower motor relay quench diode - could be the same or another or more than one in your case.

Unless you test and replace all failed (short or open) relay diodes that car is just building up expensive problems.

Don't think this is the USB issue though but it might explain the others (multiple faults).
This is a massive help, really appreciate you taking the time to be thorough with your explanation. I’ll try what you suggested and let you know 👍🏻
 
1 - 6 of 6 Posts
Top