5908 Will Not Hold Code

[pj29]

This is a new problem for me. The radio will not hold the code, so I need to input it after each time that the car is turned off.

This is a new problem, I haven't had it in the past. The dash lights work, and I already checked the fuse that controls this and the fuse was fine.

Not sure where to look next, any suggestions are appreciated.

Thanks.

[bradnic]

From our discussion you confirmed the alarm LED was flashing when the car was off, right?

When this happened to me on an old 5908 it was aftermarket battery wiring for a sub amp that was causing the code to be lost. There has to be something wrong with the dimmer wiring (white/yellow wires with white connector coming off the head unit)

I would post on (gasp) bfc too

[bradnic]

this may help - from the E30 Electrical Manual, page 6500A-0

Fuse 21 constantly supplies voltage to the Memory Power Input of the Radio. This allows the Radio to maintain the present settings while it is turned off.

also this in "Troubleshooting Tips"

Check memory power to radio by checking operation of the Glove Box Light.

The "Memory Power Input" connector is C215. it connects the the white radio connector with the yellow/white wires



This is the "Radio Power Test" procedure - check step 3


Connector C216 is the black radio power connector, which you know is working.

[bradnic]

Per discussion with Levent your headlight switch is a suspect. I thought so too, but after analyzing this further my bet is the YELLOW wire on the radio isn't getting power when the car is off. If you look closely at the first pic below the YL wire is labeled "MEMORY POWER" at the radio. The white wire is for radio night illumination. It should get power the same time the dash lights do. Just because the dash lights come on, and the radio lights up, DOES NOT mean the yellow wire is getting power though.

As mentioned above, test the voltage at connector C215 with the power on, then off, both the yellow and the white wire. Note how the yellow wire (YL) from the radio connector C215 ends up at Fuse 21, and the white wire (WT) ends up connecting to Grey/Red wires which lead to the headlight switch


You can also check connector C302 but it's probably ok. there's a 4 connector plug for the radio there per this diagram. pin V goes to Fuse 21.


The last bit is probably the hardest to read, but it's all there - the headlight switch. You can see it feeds the white wire on the back of the radio - check the highlighted box. this matches the first pic on this post
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