So I just bought this 08 civic LX (110k miles). After a few days of flawless driving, we noticed a couple wires NOT connected that were coming from the hood opener-sensor thing. Plugged them together and noticed no difference in the car until I let the car sit for about 6 hours then thats when the trouble started. Tried starting the car and the engine had trouble cranking then would stop. Pulled the key out and tried a couple more times and finally the engine started. The next day I had to do the same thing to get the car to start and now 2 days later the car wont even crank. No ticking, no cranking- nothing. Battery date is 10/14 so its coming up on 2 years old. When I turn the car to “On”, everything works (stereo, lights, headlights, dashboard lights- everything). You would notice no difference until you tried starting the car.
I havent gotten to it yet but I havent tried cleaning the battery connections. Just looking at them I cannot notice any problems or visual corrosion. Im thinking that because I plugged those wires from the hood-sensor-thing, its a bad sensor and drew current from the battery while the car was off.
If this was the case then jumping the car would probably fix it but nope, not my lucky day. Jumping the car didnt help at all and before I start checking fuses and connections I would like any insight people have on what the problem could be.
there may have been a reason why the sensor was disconnected by the previous owner. I would unplug it again, get the car jumped or battery charged and see what happens for a few days. If all works out well it’s a good indication that some type of short caused a drain on the battery. At that time you can start troubleshooting for cause. If you purchased the car from a private individual you can contact him/her for an explanation.
Edited for additional info: The hood sensor maybe connected to your alarm system. Possibly there is problem with it, preventing the engine to start. Disconnecting it may have been the solution by the previous owner.
The only thing that I would add to what @kurtwm2010 said is…
I would pull those battery cable off and clean the terminals and the posts.
And I would charge that battery instead of trying to jump it.
Jumping a completely dead battery is hard on the charging system. Once you remove the jump cables the demand for current can be more than what the alternator can handle, and this can damage the alternator.
Before you disconnect the battery, make sure you have the reset code for the radio. It may be among the papers you got with the car, or the previous owner may still have it. If you don’t enter that code into the radio after reconnecting the battery, it will not work.
I suspect whatever you reconnected is drawing current from the battery all the time. This is a parasitic draw, and it is draining the battery. You can put a volt meter on the battery and check the readings when this connection is connected and again when disconnected. If you get a lower reading connected, it is drawing current.
as kurtwm2010 added, this may be part of an alarm system. Many alarm systems have starter interrupt, and this sensor you hooked back up may have triggered that- which is a possibility as to why it was disconnected in the first place.
The fact the headlights do not dim points to an alarm system issue. Most cars do not have hood opener sensor thingies unless it is part of an alarm system. Why not just disconnect it again like when you got the car? See if the problem goes away…
Another issue worth exploring is what the sensor really does, and is it a factory item or an aftermarket add on. If it is aftermarket, I would consider ignoring it. If it is a factory item, I would consider replacing the sensor. It appears to be shorted. You could test that with a VOM.