Weird Electrical Problem with my Stereo - Page 1 - 911/Carrera GT - PistonHeads UK

1998 996 Manual Coupe. CDR22 original headunit. The stereo seems to only work when 'certain' electrical loads are on the car. What I've managed to work out: - Turn the ignition on, engine off - works flawlessly - Ignition on, engine on, cold engine - won't power on - Ignition on, engine on, cold engine - turn on AC, heated rear screen, headlights - will turn on 75% of the time, but intermittently turn off until the car is up to temp. - Ignition on, engine on, cold engine, but hot outside when sun has been on the car ...... - will turn on 75% of the time - when its hot, it seems to stay on regardless. - Iginition on, engine on, warm engine, air con off.... - will turn on.... but if I then start doing things like close the windows, if my hands stay on the button all the way to close (so like, trying to close a closed window) it will randomly turn off.... yes, that's some weird post, sorry folks, but I wanted to try and paint a bit of a picture. The battery appears to be good, voltage is showing 14v rock solid on the dash I feel it could be anything, so I don't know where to start. I'm tempted to say its *not* the headunit, because it only seems to be an issue when the car is started. Yes, I will take it to my Porsche specialist, but I just wondered if anyone had any ideas. Help ? Edited by conanius on Saturday 27th August 16:45

Are Porsches head units of that era susceptible to lo battery voltage. I know BMWs can do some weird things if the battery isn’t healthy.. Other than that that’s some random occurrences going on. Sorry cant be of anymore help other than suggesting putting the battery on charge..What’s the battery voltage when it’s running. Should be nearly 14 v if healthy and the alternator is charging it..

If the battery is healthy then I would check the ignition switch. Common for these to need replacement in a 996. When mine went bad I had some random electrical circuit faults.

conanius said: 1998 996 Manual Coupe. CDR22 original headunit. The stereo seems to only work when 'certain' electrical loads are on the car. What I've managed to work out: - Turn the ignition on, engine off - works flawlessly - Ignition on, engine on, cold engine - won't power on - Ignition on, engine on, cold engine - turn on AC, heated rear screen, headlights - will turn on 75% of the time, but intermittently turn off until the car is up to temp. - Ignition on, engine on, cold engine, but hot outside when sun has been on the car ...... - will turn on 75% of the time - when its hot, it seems to stay on regardless. - Iginition on, engine on, warm engine, air con off.... - will turn on.... but if I then start doing things like close the windows, if my hands stay on the button all the way to close (so like, trying to close a closed window) it will randomly turn off.... yes, that's some weird post, sorry folks, but I wanted to try and paint a bit of a picture. The battery appears to be good, voltage is showing 14v rock solid on the dash I feel it could be anything, so I don't know where to start. I'm tempted to say its *not* the headunit, because it only seems to be an issue when the car is started. Yes, I will take it to my Porsche specialist, but I just wondered if anyone had any ideas. Help ? Edited by conanius on Saturday 27th August 16:45 Sounds as if it’s related to consumer electrical circuit demand, and the head unit probably has a threshold voltage level below which it won’t turn on.? Try reading the 12v feed on the back of the head unit input, and see if that fluctuates under the conditions you mention. Also worth checking the battery condition with a battery tester, as well as the alternator performance under different load conditions. Ignition switch is also problematic as others have mentioned. It’s a fairly inexpensive part and easy to install. No harm in replacing it as some preventative maintenance anyway, and it then rules that item out.

Thanks for the replies folks. I've just nipped out and checked the battery, about 20 minutes after a drive to the shops. 12.5 with the engine off, started up and its ~13.7 with the air con off, 13.8 with it on. Is this the ignition switch that people refer to: https://www.design911.co.uk/fu/prod140622/Ignition...

conanius said: Thanks for the replies folks. I've just nipped out and checked the battery, about 20 minutes after a drive to the shops. 12.5 with the engine off, started up and its ~13.7 with the air con off, 13.8 with it on. Is this the ignition switch that people refer to: https://www.design911.co.uk/fu/prod140622/Ignition... 12.5V is actually quite low. How old is the battery itself. The stereo set-up you have is relatively simple, so should be easy to rectify/fault find.

Fnumber1user said: 12.5V is actually quite low. How old is the battery itself. The stereo set-up you have is relatively simple, so should be easy to rectify/fault find. No idea, I'm not going to die in a ditch if I need to replace it. Just gone out to check it quickly now and its reading 12.19/12.2 volts - not used the car today, just moved it on the drive twice, so two ~60 second uses This screams new battery doesn't it... Is there one everyone goes for, or is it absolutely fine to just get something off ECP?

conanius said: No idea, I'm not going to die in a ditch if I need to replace it. Just gone out to check it quickly now and its reading 12.19/12.2 volts - not used the car today, just moved it on the drive twice, so two ~60 second uses This screams new battery doesn't it... Is there one everyone goes for, or is it absolutely fine to just get something off ECP? Yes, at 12.2v, your battery is almost 50% discharged, so probably needs replacing. But try charging it first, and see if it can hold a charge. If it does need replacing, then chose a Bosch or Varta, and try and avoid the cheaper brands

So. I changed the battery - not knowing about the key in ignition to stop alarm going off trick. So loud it has made me go blind. In other news….. it’s annoying made little difference….. but it does seem to be pointing towards a voltage issue as now I can 100% get the radio on from cold start by having the air con and heated rear screen on. I’ve got a bit of driving to do tomorrow so that should top the battery up and fingers crossed will resolve it. If not, I’ll try that ignition switch next.

I worked as a powertrain control system development engineer for an OEM in my youth, and several times we had to diagnose and fix weird and wonderful intermittent electrical systems issues on development cars. Based on that experience, I would guess your original battery was fine and replacing the ignition switch is a sensible next step, as they are known to fail and that may be playing havoc with supply voltages (plus they are quick and cheap to replace, an important factor to consider when fault finding!) If that doesn’t work the next place I would look at is earth connections, as often when these connections deteriorate you get a “floating” earth voltage which can create weird electrical systems behaviour. To do this I’d check the major earth connections, eg battery to chassis, plus the radio ground connection. Remove any corrosion in the connection, check no wires are frayed etc, and see if that fixes things.

G-996 said: I worked as a powertrain control system development engineer for an OEM in my youth, and several times we had to diagnose and fix weird and wonderful intermittent electrical systems issues on development cars. Based on that experience, I would guess your original battery was fine and replacing the ignition switch is a sensible next step, as they are known to fail and that may be playing havoc with supply voltages (plus they are quick and cheap to replace, an important factor to consider when fault finding!) If that doesn’t work the next place I would look at is earth connections, as often when these connections deteriorate you get a “floating” earth voltage which can create weird electrical systems behaviour. To do this I’d check the major earth connections, eg battery to chassis, plus the radio ground connection. Remove any corrosion in the connection, check no wires are frayed etc, and see if that fixes things. Thanks for the detail This is the part right ? https://www.design911.co.uk/fu/prod140622/Ignition...

It looks like it but I’m not sure of the specific variant / part number for your car. If you call your local Porsche dealer with your vehicle details, eg registration number etc, they could confirm and sometimes they are actually cheaper than resellers like Design911. Plus, if you ask for a 10% discount I’ve found they often give it (they are supposed to do this for Porsche Owners Club members, but seem to do it for others if asked)