Full disclosure, I just drive em, I dont fix em. With that in mind, I could use some help/advice with what could be the problem. Any help is appreciated for my 2004 stock C5.

So Im driving home Christmas Eve and get cut off, naturally I angrily honk my horn at the guy. A Minute later my horn goes off on its own. Naturally, I hit the horn in hopes of it stopping? It does, briefly. Minutes later it activates again without me touching it. It continues for several miles until I cant take the embarrassment and punch the crap out of the steering wheel. IT stopped and I parked it for a few days. I go to start it last night (3 days later) and its dead. Interior lights all came on for a few minutes and everything appeared normal. I then hear a whirling sound coming from the fuse/relay box/battery area. All lights quickly dimmed and something drained the remaining juice that was in the battery.

Ive done some research and asked some (semi truck) mechanics at work and it seems this is a common problem with the C5 but also heard several things it could be from reading these forums.

I dont drive it daily but have noticed that when Im starting it the last few months, that the "start" doesnt seem as strong (making me obviously think I need a new battery). If it was that simple, I wouldnt be asking for help. It seems like something else is going on? Something is running/draining the battery? Ive removed the horn relay and fuse, jumped it and it worked. Once it sat again, the whirling sound happened again and battery was drained QUICKLY. Ive had the car 3 years and never had to replace the battery.

Obviously I should start with a new battery. But if that isnt 100% of the problem, wouldnt a new battery just be drained by this issue as well? Anyone else had a similar issue?

Sorry for writing so much, but I wanted to be as clear as possible. Thanks in advance for any help!

 

I would say there is a strong possibility that the horn membrane is broken.

 

You need to have the battery fully charged and load tested. A battery with a bad cell will not hold a charge. You can't determine if you have a drain until you are sure the battery is good.
Most of the auto parts stores will test the battery for free.

 

Your horn staying on after use would seem to be the membrane. I don't think it would fail to provide a drain without making the horn sound. Of course your temper to hit the horn could have created a short to ground so you had a drain but no horn activation. However with the fuse out now there should be no drain from that circuit.

Would seen you have a bad battery or a drain. The membrane is another issue so long as the battery drained with the horn fuse out.

Load test your battery to start with. If it tests good then we will have to find the drain.


Mr. Sam

 

I AGREE! The battery needs to be removed, fully charged and then fully tested. It has to have the full RESERVE CAPACITY that its rated for as well as the proper Cold Cranking Amps (CCA)

Once you get the battery properly sorted out (properly tested and charged or replaced),, Reconnect the POSITIVE battery terminal. Obtain a DC Amp Meter (multimeter) and set it up to read 10 AMPS. Most multimeters will have a separate 10 amp function.

Connect the AMP METER in SERIES with the negative battery cable and the NEGATIVE battery terminal. That will allow you to see how much actual CURRENT the electrical system is drawing when the car is in the SLEEP/SECURITY MODE. After the connection, within 10-12 min, the reading should settle in on approx 20 milliamps.

IF,,,,, the reading is high, you will need to figure out what electrical component is not shutting down when the ignition is OFF.

Some of the most common things that cause this issue are:

- Seat Motors caused by a defective seat multifunction switch
- Seat Lumbar motor/pump
- Interior lights left on
- Hood light doesn't shut off
- HVAC Fan doesn't turn off (usually on the dual mode system)


Anyway,,, see if you can zero in on where the noise is coming from once you get the battery back in the car.

Bill

 

Very helpful, thank you!

 

You're welcome!

 

I did exactly that and it wasnt holding a load. Apparently these cars do all sorts of things when a battery is needed. I just wasnt used to it because my C4 didnt do anything like this. Thanks for the help!

 

Thank you so much. It ws the battery. It wasnt holding a charge. IT just confused me because the horn was acting up at the same time. All is well.

 

Welcome the electronic world of the C5.



Good luck.


Mr. Sam