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How do I troubleshoot a short in my 2004 Impala LS 3.8l?
The heat killed my car today. I parked it this morning and in the afternoon it wouldn't start. I thought the battery had drained and decided to try cleaning the battery terminals to see if I could coax it to start. As I reconnected the negative, it started sparking! I verified with my multimeter that, indeed, there was 12.8VDC coming from the frame! My guess is that some insulation melted on a wire and shorted it to the frame SOMEWHERE in the car. But isolating it is gonna be a pain. I tried pulling every fuse and relay in all four fuse boxes while my daughter watched for the multimeter to see if the voltage went away but no such luck. (I was hoping to isolate the circuit where the short was.) I left the negative terminal disconnected to avoid any further damage.
Any suggestions on how I might isolate the circuit where the problem is and avoid ohming out every wire in the flipping harness? A new car is out of the question for at least several months and I am a service rep for office machines so I live in my car. (I mean that metaphorically - the pay's not THAT bad - lol!)
Thanks in advance!
MIchael: I appreciate the response. The technique I used was putting the black lead of the multimeter on the negative battery terminal and the red lead on the ground cable (while the cable was disconnected.) It kept a constant 12.8VDC (which was the voltage across the battery terminals as well) for at least fifteen minutes or so. I would have expected, if I were shorting a capacitor, to see the voltage drain (which I think is what you're saying about the lamp dimming) but it just stayed there.
Humvee: I agree that a short isn't likely to just appear while it is sitting there. That's why I thought maybe some insulation melted. The heat was above 100 degrees here today, and this car has 270K on it so if something was marginal, it might have gone. I really didn't expect 12V from ground to ground, but given your answer, maybe I'll take the battery over to Autozone tomorrow and make sure it is fully charged, then put it in and try to start up. This is how the car has acted to a dead battery a couple of times in the past, so maybe it is a "ghost." At any rate, it sure is a gremlin! Thanks for the response.
3 Answers
- HumveetechLv 710 years agoFavorite Answer
Are you sure your not chasing a ghost??? As for the sparking on the negative side, I deal with a few cars that do emit sparks when connecting the negative side of the battery. Cadillac's do it everytime. Most cars with a lot of electronics with also do that, it is just your waking up a few modules when connect the battery. As long as the cables are on correctly, it wont hurt as long as it isnt a lot of of sparks, that would be the question on how much sparks are there involve??????
I cant see your car all of a sudden acquiring a short from sitting with out any signs of a problem up to that point when you parked it there. Most cars are protected with fuses unless you wired a after market stereo system or trailer hitch & wiring for the trailer but even those will cause the wire to melt unless you used 6 gauge cable. But for any small diameter wire to be grounded directly to the ground, would have to be straight from the battery maybe the one to the starter but a few of those wires have fusible wires that will open if too much current flows through them.
- FlagMichaelLv 710 years ago
Rather than a short, I suspect you are seeing input capacitors on some of the electronics (especially the air bags) charge. If you have a spare bulb for a turn signal or similar you can use that to test. Hold the shell of the bulb against the cable and place the connection nub(s) against the battery post. It's okay for the lamp to flare up but it should dim to the point you can't see the glow in daylight within a couple seconds.
- cullinanLv 44 years ago
Why dont you sell the Impala, use the proceeds from that and the $$ you have been going to spend on the sides and purchase a greater effective automobile. An Impala on 20's or 22's continues to be an Impala...
