2001 SAAB 9-5 battery dies - hum from speakers with car off

Tiny
LCAMEL
  • MEMBER
  • 2001 SAAB 9-5
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 99,700 MILES
I have a 2001 9-5 SE wagon which I purchased just a couple weeks back. A few days after purchase I noticed that about 10 seconds after the ignition is turned off a very low/quiet hum would start up from the car's speakers. If you turn the ignition on the hum will stop. Also, if you turn the radio on (with the ignition off) the hum stops. Turning the radio off the hum will start again after 10 seconds.

Ignition ON and/or radio ON = no hum
Ignition OFF and radio OFF = hum

Up until this last week the car had been working fine but then the battery went dead after it sat unused for a couple of days. I recharged the battery and the car is running fine but I suspect the battery going dead has something to do with this hum and it will soon happen again. Appreciate any thoughts or advice on how to diagnose this issue.
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Monday, April 5th, 2010 AT 10:04 PM

7 Replies

Tiny
CARADIODOC
  • EXPERT
Dandy observations. Look for a factory remote-mounted amplifier. If there is one, it might not be turning off. These systems usually have a dedicated fuse that you can remove as a test.

In rare cases, the radio's memory circuit also powers the audio output stages in the radio but turns off separately. If that circuit is staying on, the radio will have to be replaced. You can find that by removing the memory circuit fuse, but it is usually tied in with some other circuit that is always live. Interior lights is a common fuse that feeds the memory circuit. The cigarette lighter and horn circuits could also be used.

Caradiodoc
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Monday, April 5th, 2010 AT 11:25 PM
Tiny
LCAMEL
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Very good, the amplifier staying on appears to be the problem. I pulled a fuse for the "audio amplifier" and the hum went away. Would the amplifier stay on solely due to the malfunction of the radio memory circuit or is that just a potential cause? I tried removing other fuses for interior lights, etc. But I could not get the hum to disappear. As I understand it there's a trigger voltage from the radio which causes the amplifier to power on. Is it correct that the removal of that trigger voltage will cause the amplifier to power off? So if I can see the trigger voltage from the radio is not being removed when the radio is powered off then the problem is with the radio unit?

I don't see a fuse labeled "radio memory circuit"
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Thursday, April 8th, 2010 AT 11:44 AM
Tiny
CARADIODOC
  • EXPERT
Let me start out by saying there might be a security code needed to make the radio work after power is removed. I don't know if that applies, but if it does, be sure to know the code before disconnecting it or pulling fuses.

The easiest way to find the culprit is to disconnect the radio, then see if the amp turns off. If it turns off, and turns right back on when the radio is reconnected, the radio would be suspect. If the amp stays on, a relay could be sticking on. An alternative to pulling the radio is to remove the two fuses. One is for the switched power that turns the radio on with the ignition switch. The fuse for the memory circuit is usually tied in with some other circuit that is always on. Interior lights is the most commonly used circuit, but the horn or brake light circuit could also be used.

Most radios will not switch the amp on and off directly because that's a lot of current for the switch to carry. Instead, the radio typically turns on a relay. The problem is, that relay could be in the dash, in a fuse / relay box, in the amplifier itself, or an electronic circuit in the amp. I'm sorry I don't know where that relay lives, but if you can find it, it will provide clues if it clicks off when you pull it out of the socket.

Caradiodoc
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Thursday, April 8th, 2010 AT 6:25 PM
Tiny
LCAMEL
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With ignition off and radio off, the hum continues when I pull the radio fuses (9 alone, 21 alone or 9+21 together) and stops when I pull the amplifier fuse (13). You advised that there may be a relay which is controlled by a trigger voltage from the radio and that relay is stuck. The wiring diagram in the Haynes manual does not indicate a relay between the radio trigger (pin 7) running to the amplifier (pin 12). Does anyone know if this amplifier has a built in relay? If this is the case then I assume I need to replace the amplifier, Saab / Harmon/Kardon part #4713699.

BTW - The Saab radio and CD are mated to the car via Tech2 programming and must be divorced/mated if moved to another car. Removing power doesn't cause the radio to lock.
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Saturday, April 10th, 2010 AT 5:22 PM
Tiny
CARADIODOC
  • EXPERT
The only other thing you can check is if there is voltage on that pin 12 on the amp. If there is, it is coming from somewhere and is turning on the amp. Unplug the amp, then measure again on pin 12. If voltage is there, we need to determine where it's coming from. If the voltage is gone now, it was coming from inside the amp. If there is no voltage on that wire, the turn-on circuitry inside the amp is not turning off. Apparently fuse # 13 is hot all the time. That seems strange since the amp should never be powered up when the ignition switch is off. They are obviously relying on the power switching circuitry to do the job.

I suppose some enterprising individuals might try to rewire the power wire for the amp to a different voltage source that is switched off with the ignition switch. Normally an amp should not need a memory circuit when the ignition switch is turned off, but there must be something going on with the programming to the car that requires the power circuit to remain hot at all times. Rewiring what the engineers designed is rarely the right approach, especially when we don't always know their reasoning.

I want to apologize in advance if I take a long time to reply. My Verizon personal e-mail provider is going through some major changes, (not for the better), and they're going out of service about 20 hours per day. When you post a response, I get an automated e-mail message directing me to it. I have to watch 24 hours per day to quickly find those messages during the few hours the system is working.

Caradiodoc
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Saturday, April 10th, 2010 AT 11:45 PM
Tiny
LCAMEL
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I think it's hot all the time to allow the radio to be turned on even when the ignition is off.

On the assumption that it was a broken relay in the amplifier I located a used amplifier on ebay and swapped it for the one in the vehicle. Hum is gone, audio system works great and no more dead battery. Thanks for your assistance.
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Friday, June 4th, 2010 AT 1:29 AM
Tiny
CARADIODOC
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Wonderful. Happy to hear the good news.

Caradiodoc
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Friday, June 4th, 2010 AT 1:37 AM

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