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Discussion Starter #41
The above test is performed with the 2 connectors detached from the BCM unit.

Now, another tests, the 2 connectors attached, and join one end of multimeter is joined to the input pin and other to the ground.

The voltage is 0v. As soon as key is at ON, voltage comes to .60 v. And, when defogger switch is now pressed, the voltage drops to 0 Vol again. Is this normal??
 

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The voltage is 0v. As soon as key is at ON, voltage comes to .60 v. And, when defogger switch is now pressed, the voltage drops to 0 Vol again. Is this normal??
No, I don't think that is normal. I'd expect there to be a much higher voltage on the input wire when the switch is at rest (not pressed). Maybe 3.3 or 5V. Certainly more than 0.6V.

Have you checked ALL the fuses recently, by probing the test points on top of each fuse with your voltmeter (ignition on).

 

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Discussion Starter #43
Wooow, very interesting....we are moving on........ let's try not to hurt this beautiful cool Car i20.....

Let me check them all.....
 

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Discussion Starter #44 (Edited)
What if I got some fuse has 12.60 Vol on both ends and some has 12.10 or 12.30 or 12.45 on both ends as well where the true battery voltage is 12.60?? They are just marginal difference. Will it make any sense??

Here's the fuse box under the steering wheel.
441051
 

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Discussion Starter #45 (Edited)
Every fuses have the same readings on each ends individually.

Surprisingly, one 10 amp fuse shows 12.03 v on each ends and another 10 amp fuse has 12.06 v on each ends..etc.... likewise some 15 amps of different locations shows different readings...and some shows same readings, however, I guess these readings are not related to our issues.

How to get either 3 or 5 volt to this input wire??? Where is this .60 v coming from??

I also checked for the ground wire on the output connector detached from BCM , however, none of the wire shows continuity. Here's the results.
441053
 

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Discussion Starter #46
Another tests....by bypassing the BCM.unit....and the switch control panel...

I ground the input wire located at the switch panel connector and Yes, the relay clicks with 12 v reading on multimeter. (the resistance is just 3 ohms which refers that the about 205 resistance is inside the control panel switch module)

Problem is 205 resistance inside the rear defogger switch control PCB module!!! This resistance is normal or ......very confusing now???
 

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Right, so the resistance is supposed to be there so that's not the problem. "I think" the problem is the circuit inside the BCM. I'm pretty sure there should be some voltage on the BCM input wire and yours has none. Just connecting that wire to an external voltage source isn't likely to help. The voltage that should be there comes from the electronic circuit inside the BCM. My guess is that electronic circuit has failed in some way. But that is only a guess. The only way to know for sure would be to compare your circuit the a working circuit on another i20. Unfortunately I don't have access to another car so I'm unable to help with that...sorry.
 

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Discussion Starter #49
We both are on the same idea now...all components from input side till the input connector at BCM are ok.

Also, from the output connector from BCM till the relay are ok.

Now, headache on the BCM UNIT as suspected by you and myself... however, we would try finding the solutions to this particular issue in coming days....

Always welcome your comments and suggestions.... thanks once again....
 

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Discussion Starter #50
Just to update.....this morning I started the car...and engine running....O God!!!! The rear defogger comes on.....

Engine off..and wait sometime around 5 minutes, and restart the car. Repeat this process more than 5 times, yes, it still works TILL AT THIS MOMENT!!!😇😇😇

(Actually, the test should be carried out with engine running as against the earlier test with engine off😅😅😅)

Also, I guess that little voltage .60 at the input wire is Ok though I have not retested it.

Thanks once again for your valuable inputs and suggestions!
 

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Actually, the test should be carried out with engine running as against the earlier test with engine off😅😅😅
Your absolutely correct. The defogger will only function when the engine is running so you should really have the engine running while testing.

Thang Tons said:
Also, I guess that little voltage .60 at the input wire is Ok though I have not retested it.
Test it now while it's working (with the engine running). Then if it fails again you'll have some data from a known good circuit to compare your faulty circuit measurements to.

Thang Tons said:
Thanks once again for your valuable inputs and suggestions!
No problem. Your threads always give my brain a good workout 😀
 
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