Hi, my 06 Octavia has recently developed a problem were it will intermittently raise its idle to about 1050 rpm. it doesnt happen all the time but is getting more frequent. It happens more so at night with more load on the electrical systems ie lights heater radio so on. But does still happen during the day with just the radio running. The computer is showing a fault code for drive voltage supply. When it idles high the fans also are not always on like some other users have said happens with theirs. 

 

when the ignition is turned on the stereo (which is an aftermarket sony unit with carplay) will come on like normal and about 30 seconds later it will lose power. the stereo itself seems fine and ive measured across the wires that the car itself stops sending power to the unit over the 12 volt cable (red) but the yellow cable still has 12 volts. The battery seems fine with a voltage of about 12.4 and with the engine running just over 14. so would seem to me the battery and alternator are working ok.

 

My mechanic is also stumped as he cant see any obvious reason it would be idleing high.

Increased revs to try to recharge the battery, more so when additional load loads are switched on, plus radio turning off are all signs of low capacity in the battery.

This can be caused by the battery being near end of life or the alternator not supplying enough recharge current. My bet would be on the battery as it would read the correct voltages, steady state, with a reduced capacity.

How old is the battery? Are the connections clean? Are the body connections to the alternator and battery good with no sign of corrosion?

The supply to the radio (and some non essential loads) is shut off automatically if the system detects reducing battery voltage.

 

 

 

43 minutes ago, pikpilot said:

Increased revs to try to recharge the battery, more so when additional load loads are switched on, plus radio turning off are all signs of low capacity in the battery.

This can be caused by the battery being near end of life or the alternator not supplying enough recharge current. My bet would be on the battery as it would read the correct voltages, steady state, with a reduced capacity.

How old is the battery? Are the connections clean? Are the body connections to the alternator and battery good with no sign of corrosion?

The supply to the radio (and some non essential loads) is shut off automatically if the system detects reducing battery voltage.

 

 

 

When I used to work as a motor home technician we used to ‘drop test’ the leisure batteries to assess the battery under load and amazing how many would fail but pass a no load voltage check.... and low voltage would make sense of the problems. Or possibly a bad/corroded electrical contact causing a similar fault.x

I forgot to say, check for corrosion in the fuse box near the battery. Water ingress can corrode the fuse holders and the fuses and has been found on older cars. Check also for overheating/melting of the plug in fuses as a result of poor contact.

 

Ill have a look now for the corrosion if any. Thanks guys!!

 

I have the carly app and its showing that the voltage is does drop to just below 14 with lights on but with the radio still not on.

 

 

so after replacing the battery, the issue of the revving has gone away but the radio still came on but turned straight off. the error code is also gone. i installed the original radio back into the cra nad that seems to work just fine leading me to belive the radio was at fault from the get go.