What's wrong with the car stereo in my 2003 Nissan Sentra?

October 18, 2009 10:31 AM

What's wrong with the car stereo in my 2003 Nissan Sentra?

I have a Blaupunkt MP3000 dash unit which has served me well. I had it professionally installed shortly after purchasing the car (new-ish), and until recently I've had no problems with it. (No external amp or anything fancy like that—just the head unit.)

A couple of months ago, the audio started cutting out intermittently. Going over a bump in the road will often cause it to cut back in briefly—and it worked for a short while after I removed the dash panel and disconnected and reconnected the wiring clips—but those periods of functionality have gotten shorter and shorter, to the point where I only hear an occasional split-second of radio when I cross a rough train track. It's not any one speaker that's cutting out; they're either all working, or (more often) all not working.

The Blaupunkt is receiving power, and from all indications is performing normally—the channel meters show that an audio signal is present, and everything works the way it should. It doesn't matter whether the signal is coming from the radio, the CD player, or the aux input—it's just not getting to the speakers.

I tried removing the Blaupunkt and putting the original factory unit back in—and got the exact same behavior. Unit gets power, seems to function normally—but no audio.

Since it's getting power, it shouldn't be a fuse issue, but just for shits I checked all fuses that sounded relevant—under the hood, inside the cabin, and on the rear of the Blaupunkt—and all of them look fine.

When it was still working for short periods of time, it seemed like it would cut out again when the signal got loud (e.g., if I turned it up moderately loud, or when the broadcast/CD peaked)—but I couldn't be certain of that.

(If it matters, I replaced all four factory speakers with new Kickers a few months ago.)

So what's the deal? I thought those eight wires coming from the back of the head unit connected directly to the four speakers. So how is it that two otherwise functional head units are failing to power all four speakers? The behavior with bumps in the road suggests a loose wire/component, but what single point of failure could possibly cause this behavior?

Obviously I'm misunderstanding something here—do the four speaker signals pass through some common component inside my Nissan before they get to the speakers?

Any suggestions would be welcome—I'm starting to go crazy without music in the car, and I can't really afford to take it to a professional right now, and besides I'd rather fix it myself, if I can.

posted by ixohoxi to technology (7 comments total)

Was this one of those setups where the new head unit came with its own connector harness that you splice the existing harness into or is it entirely plug-and play?
posted by Jon-o at 10:43 AM on October 18

Further reading suggests that the signal coming from the back of the head unit is only pre-amped, and does in fact go through a factory amplifier of some kind before reaching the speakers. I Did Not Know That.

If that's the case (and please confirm or deny it if you can), I think I've identified my problem—and I just need to figure out where the sucker is.
posted by ixohoxi at 10:43 AM on October 18

The factory wiring inside the dash consists of two rectangular plastic clips/sockets and an antenna connector, which plug directly into the factory unit. The Blaupunkt, however, is connected with an adapter harness (sorry, I don't know the right terms)—one end has a matching pair of plastic sockets, and the other a single socket which plugs into the Blaupunkt.

Hope that's clear.
posted by ixohoxi at 10:46 AM on October 18

...okay, ignore my first comment. The article I was reading glosses over the distinction between the head unit's pre-amp and power amp outputs.
posted by ixohoxi at 11:06 AM on October 18

And all the pins in the factory harness terminals and the the aftermarket adapter look ok, right?
posted by Jon-o at 12:28 PM on October 18

IMO... you've eliminated the radio, power, and speakers. Your problem is in either the cable(s) or the connectors. Since all 4 speakers are cutting out at the same time, it's gotta be in the connector. It seems to be the only thing common to all configurations and one which adequately explains all symptoms.

The connection is initially working, but marginal.

Concentrate on the connector. If it's the typical Molex white nylon type, it has latches that assure that vibration does not work the connections loose. These are positive.. clicking types of ramps that are hard to get apart if they are done right. if your connectors are relatively easy to disconnect, they aren't seated properly. Properly seated connectors will be hard to pull apart.
posted by FauxScot at 12:30 PM on October 18

...make that 'impossible' to pull apart, not 'hard'.
posted by FauxScot at 12:31 PM on October 18