E38 widescreen monitor doesn’t work when key at ignition position.

[Chalkie 1]

If key is in accessory position (1), everything works fine. 

If key is in ignition position (2), the radio controls (in fact all the controls on the widescreen monitor) stop working, and the display stops updating.  If I switch the key back to 1, everything works fine again.

Here’s what I’ve tried so far:

 

- substituting the boardmonitor for a presumed good one 

- disconnecting the Nav (Mk 4) to allow the video module to drive the display

- swearing at it

 

Any ideas?  Video module?  Main computer?  Wiring?  God hates me?

 

Cheers!

[B.M.W Ltd 950]

Check the back of the ignition switch plug for output voltages with a volt meter not an LED probe. Ignition switches are a known fault

[Chalkie 1]

1 hour ago, B.M.W Ltd said:

Check the back of the ignition switch plug for output voltages with a volt meter not an LED probe. Ignition switches are a known fault

Ok cheers will check that and update. 

[Chalkie 1]

Update: the steering wheel radio controls don’t do anything when this issue occurs.  After 5 or 10 seconds, the display goes blank.  Will check ignition barrel switches as recommended above. 

Edited July 10, 2018 by Chalkie

[_ethrty-Andy_ 2136]

just worth buying and replacing regardless of if its your fault.. they are common to fail.

when the radio does its quirk, press the horn and see if that goes.

[Chalkie 1]

I suspect the issue is iBus-related.  Will confirm.  

[Chalkie 1]

Wow.  I-bus drops to zero volts when key is turned to on (position 2).  That is really interesting, as ibus is active-low - usually 12V, then pulled low by devices as required.  This means either the main brain has something fruity going on, or some device that’s not on in accessory position is coming on when key is on, and dragging the ibus down to ground 0V.  I’ll disconnect ibus line from the brain and see if it stays high on the brain.