factory Pioneer Amp fuse keeps blowing? Solved in post #6!

[potus98]

2005 Chevy Cobalt LT with factory upgraded Pioneer sound system. No upgrades or mods of any kind. No OnStar or SatNav.

I assume something is shorted/broken because the amp fuse is immediately blowing. The fuse is located in slot 6 of the fuse block in the passenger foot well. After the amp fuse blows, the stereo and all other electronics continue to work, but no sound is produced by any speakers. (I say the stereo "works" since it can turn on, change stations, read a CD, etc. but no sound is produced.)

To try isolating the issue, I disconnected negative battery terminal, removed the stock Pioneer amplifier, replaced fuse, reconnected battery; fuse still blows. Removed head unit, repeated test, same result. Disconnected all speakers (including sub), repeated test, same result.

Also tried different 20A fuses from different stores/manufacturers to make sure didn't get a bad batch.

So, the head unit and amplifier are out of the car and all speakers are disconnected. With negative battery terminal disconnected, replace blown fuse, reconnect battery, fuse blows.

* What is my next troubleshooting step?
* What other devices use the 20A "amp" circuit?
* Is there a way to test the fuse block itself?

Thank you!

[newfiedan]

you will need to find out if there is any other devices on that fuse but you have a dead short to ground for sure, I would be checking the wiring for the amp, trace it along the path and see if there are any places where the wiring has been rubbed or broken through. Short of that you would need more diagnostic tools to tell you where the short is located.

[emperorjj1]

the amp could very well be blown too

[potus98]

Thanks for the feedback!

Originally Posted by newfiedan you will need to find out if there is any other devices on that fuse

My Chilton manual doesn't have Pioneer sound system wiring diagram. i.e.: no diagram showing what's on the "amp" fuse. Can't find on web either. Suggestions on how to find other devices on same circuit?

Originally Posted by newfiedan I would be checking the wiring for the amp, trace it along the path and see if there are any places where the wiring has been rubbed or broken through.

Can anyone suggest locations where rubbed wires tends to happen on a Cobalt?

Originally Posted by newfiedan Short of that you would need more diagnostic tools to tell you where the short is located.

What diagnostic tools should I use?

Should I do such testing with or without the car battery connected?

Is there a tool that can be grounded to the chassis, then probe the connector pins on the stereo-related wiring harnesses to find a short?

Thanks again!

[newfiedan]

emperorjj1 the amp could very well be blown too
He removed the amp and it still blew the fuse, so that is not the problem.
Now with that said I would be looking at where the seats fold down. along the door sill areas and the like, basically anywhere that there are moving parts and remove the lower portion of the back seats. They come out pretty easy so its not to hard. There are specialty tools to trace shorts they send an echo pulse down the wire and you can use a tracer to run along the harness to see where the echo ends, but a decent digital auto-ranging multimeter can be used to do the same job just with a little patience. I do not have access to the wiring diagrams for the cobalt sorry to say. But I would start with checking the wiring for that amp and work my way towards the front of the car.

[potus98]

Thanks for taking the time to respond and inform. Explaining what I found in detail since the cause of this issue could have affected a variety of circuits. It just happened to show up with the amp circuit.

Problem: Over time, wires rubbing against mounting bracket cut through insulation and shorted to the chassis.

Location: In the dash behind the radio and AC controls. There is a vertical mounting bracket that holds the fuse block. There are a variety of bends and holes, but the bracket basically starts to the left of the glove box and goes down behind the radio, AC controls, expands to provide a frame to which the fuse box is mounted, then connects to the hump/floor at the bottom.

A bundle of wires exits the fuse box on the left (driver's) side of the fuse box. (Opposite side from the fuses themselves.) This bundle loops down then up (slack loop) to join a bundle of wires running horizontal behind the dash.

As the bundle of wires leaving the fuse box routes up, they end up resting (not strained) against a metal edge of the fuse box mounting bracket. The design of the bracket, along with the installation method of the wiring bundle, suggests the same issue could arise for other circuits and other Cobalt owners. A total of 4 wires were being compromised -the amp circuit just happened to fail first.

In the end, it's ironic that the fuse box mounting bracket is what cut the insulation and caused the short.

[newfiedan]

Excellent find so I suggest we sticky that for future cobalt owners to go in there and check that out as a preventative measure.

[YelloEye]

Stuck thread, also changed the title a bit to reflect the solution.

[emperorjj1]

interesting... lol if i wasnt so lazy nowadays id look at my car and double check