Horn relay gets hot and blows fuses
05-28-2017, 11:14 AM
#1
Horn relay gets hot and blows fuses
Horn hasn't work on the car since I picked it up. Checked the codes and I have B2527 H C Horn Relay Circuit.
So I open up the fuse box, and the horn fuse is blown. I replaced it, and it immediately blew again. Now, I noticed that the micro relay for the horn was really hot, and this was after the car had been parked overnight (none of the other relays were above ambient temp).
Thinking it could be the relay, I stuck a spare in there (having not replaced the horn fuse), and it too got super hot within a few minutes.
I'm guessing this was a potential source of battery drain. So there is a short circuit somewhere that causes the fuse to blow and the relay to heat up like that.
How do I find it?
Oh, I should also mention that as I stuck the spare micro relay in there, I could hear it clicking open/closed. So something was causing the relay to switch. I'm not sure if that is normal for the horn relay or not.
So I open up the fuse box, and the horn fuse is blown. I replaced it, and it immediately blew again. Now, I noticed that the micro relay for the horn was really hot, and this was after the car had been parked overnight (none of the other relays were above ambient temp).
Thinking it could be the relay, I stuck a spare in there (having not replaced the horn fuse), and it too got super hot within a few minutes.
I'm guessing this was a potential source of battery drain. So there is a short circuit somewhere that causes the fuse to blow and the relay to heat up like that.
How do I find it?
Oh, I should also mention that as I stuck the spare micro relay in there, I could hear it clicking open/closed. So something was causing the relay to switch. I'm not sure if that is normal for the horn relay or not.
Last edited by JagYouAre; 05-28-2017 at 11:16 AM.
05-28-2017, 01:19 PM
#2
Thanks, this is great information. Will be very helpful.
Let me just make sure I understand how this works...
So basically, fuse 11 can't blow unless the relay is closed (even if the green wire were shorted to ground, it wouldn't do anything to the fuse until the relay was closed). So we know the relay is getting a signal to be closed.
Now, if the relay were closed, and there was no short on the green wire to ground, fuse 11 wouldn't blow and the horn would sound.
So two issues:
-constant signal telling the horn relay to close and fire the horn. most likely the membrane
-short somewhere on the horn side of fuse 11 to ground
When I stuck the spare fuse in, the horn didn't sound either, even for a split second before the fuse went. That would make sense with this explanation.
Thanks again for the information. Will see what I can do, which is limited at the moment since I don't have a lift or jack stands haha.
Let me just make sure I understand how this works...
So basically, fuse 11 can't blow unless the relay is closed (even if the green wire were shorted to ground, it wouldn't do anything to the fuse until the relay was closed). So we know the relay is getting a signal to be closed.
Now, if the relay were closed, and there was no short on the green wire to ground, fuse 11 wouldn't blow and the horn would sound.
So two issues:
-constant signal telling the horn relay to close and fire the horn. most likely the membrane
-short somewhere on the horn side of fuse 11 to ground
When I stuck the spare fuse in, the horn didn't sound either, even for a split second before the fuse went. That would make sense with this explanation.
Thanks again for the information. Will see what I can do, which is limited at the moment since I don't have a lift or jack stands haha.
Based on your symptoms I suggest that there are 2 separate issues going on. The horn wiring circuit is pretty simple. Here is the diagram:
Attachment 48098044
As you can see the top of relay 36 is electrically hot all the time. The horn can be operated by 2 separate means. A) pressing the center of the steering wheel B) BCM can activate it (for example if you have the options configured to sound the horn when you use the FOB to lock the doors).
Operation is straight forward. With voltage always at the top of the relay the bottom of the coil side of the relay (C8) is grounded by either the horn switch or the BCM. This closes the contactor side of relay 36 and delivers battery voltage to fuse 11 and then to the horns.
The relay being warm (with no fuse 11) says that there is a constant ground to the bottom of relay 36. Should normally be an open until there is a call for operation of the horn. So either the membrane switch in the driver air bag is stuck closed (a somewhat common C5 problem) or the BCM is constantly calling for horn operation (unlikely but possible). There could also be a short to ground of the black wire to the horn/BCM that is causing the coil portion of the relay to constantly be grounded. IMHO it is likely the membrane switch.
Even given the constant operation of the coil side of relay 36, if the path between fuse 11 and the horns was not shorted or the horns were operable the horns would constantly sound and NOT blow fuse 11. Fuse 11 blowing says that either the horns are bad or there is a short to ground of the green wire between the horns and fuse 11.
I would start with the horns. They are behind a protective cover on the front bottom of the passenger side.
http://forums.corvetteforum.com/c5-t...placement.html
I would disconnect the wires to the horn at the horns and insure they do NOT touch any metal. Then replace fuse 11. If it immediately blows then the green wire is shorted to ground. If the fuse does not blow then use a digital multi meter to measure voltage at the green wire. Should be battery voltage. If so the horns are causing an excessive current draw blowing fuse 11. Replace the horns to correct this problem.
The most likely cause of the constant ground to the coil side of relay 36 is the membrane switch. Here are a couple links about the membrane switch problem:
http://tech.corvettecentral.com/2012...rn-switch-fix/
http://forums.corvetteforum.com/show....php?t=1739923
Then post #39 on page 2 for replacement membrane. At one time Ecklers and Mid America had the replacement membrane switch available. I have not checked in a couple of years. I got mine from Ecklers.
The GM solution to the membrane switch failure is replace the air bag module as they offer no service parts. An aftermarket company does offer a replacement switch but it is a bit of effort to replace.
Until you resolve the issue with the constant ground to the coil side of relay 36 I suggest you remove the relay. Not doing so means a constant drain on the battery that was never intended.
Attachment 48098044
As you can see the top of relay 36 is electrically hot all the time. The horn can be operated by 2 separate means. A) pressing the center of the steering wheel B) BCM can activate it (for example if you have the options configured to sound the horn when you use the FOB to lock the doors).
Operation is straight forward. With voltage always at the top of the relay the bottom of the coil side of the relay (C8) is grounded by either the horn switch or the BCM. This closes the contactor side of relay 36 and delivers battery voltage to fuse 11 and then to the horns.
The relay being warm (with no fuse 11) says that there is a constant ground to the bottom of relay 36. Should normally be an open until there is a call for operation of the horn. So either the membrane switch in the driver air bag is stuck closed (a somewhat common C5 problem) or the BCM is constantly calling for horn operation (unlikely but possible). There could also be a short to ground of the black wire to the horn/BCM that is causing the coil portion of the relay to constantly be grounded. IMHO it is likely the membrane switch.
Even given the constant operation of the coil side of relay 36, if the path between fuse 11 and the horns was not shorted or the horns were operable the horns would constantly sound and NOT blow fuse 11. Fuse 11 blowing says that either the horns are bad or there is a short to ground of the green wire between the horns and fuse 11.
I would start with the horns. They are behind a protective cover on the front bottom of the passenger side.
http://forums.corvetteforum.com/c5-t...placement.html
I would disconnect the wires to the horn at the horns and insure they do NOT touch any metal. Then replace fuse 11. If it immediately blows then the green wire is shorted to ground. If the fuse does not blow then use a digital multi meter to measure voltage at the green wire. Should be battery voltage. If so the horns are causing an excessive current draw blowing fuse 11. Replace the horns to correct this problem.
The most likely cause of the constant ground to the coil side of relay 36 is the membrane switch. Here are a couple links about the membrane switch problem:
http://tech.corvettecentral.com/2012...rn-switch-fix/
http://forums.corvetteforum.com/show....php?t=1739923
Then post #39 on page 2 for replacement membrane. At one time Ecklers and Mid America had the replacement membrane switch available. I have not checked in a couple of years. I got mine from Ecklers.
The GM solution to the membrane switch failure is replace the air bag module as they offer no service parts. An aftermarket company does offer a replacement switch but it is a bit of effort to replace.
Until you resolve the issue with the constant ground to the coil side of relay 36 I suggest you remove the relay. Not doing so means a constant drain on the battery that was never intended.
06-01-2017, 11:55 PM
#3
I think my membrane switch may be out because I hit my horn to toot warn a fella with a helmet riding a 2 wheeled gadget powered by his legs on a narrow road on a turn that I was coming up on his back side and my horn got stuck!!!! It stayed stuck for a minute as I banged on the steering wheel and mashed the pedal to get away. Got home and the fuse was blown. Went to put another fuse is and the horn was on. We will see. Great info here. Hope your laughing now.