S80 Communication with UEM signal missing.

[Ummi60]

Hello.
I recently bought a second hand s80 (2002, 2.4D5).
And noticed that the key fob didnt work, nor did the ceiling lamps. A couple days ago i got my Vida/dice device from china and got it running on my laptop. A quick scan later reveals CEM-1A5C (Communication with UEM. Signal missing) trouble code.
Wierd thing is, the lights dont work until i read the codes (or unplug and plug back in the dome light fuse), at which point the dome lights start working again (for some time).
(I also have a UEM-0004 (Siren communication fault DTC), but im not that troubled by this since they keyfob doesnt work and all the doors still lock when turning the driver door lock. [Would be nice to get the alarm working but its not that big of a priority])
Has anyone dealt with this problem before? How do i fix it?

Thanks in advance!

[SwissXC90]

Check power and ground and can bus to the UEM.
You may need an oscilloscope to check the CAN bus signals

Try a total vehicle reset: either disconnect battery, or issues software reset command in VIDA.

Ensure battery is full charged.

If all of the above makes no change, you may have a defect UEM.
Read about the UEM in Vida. You will see that it houses the remote control receiver for the keys.

You will see that it is coded to the car and that only a brand new unfolded UEM can be coded by VIDA.
You will see that UEM coding is a dealer only job

[harveys]

Try unplugging the alarm siren unit incase it's shorting out the UEM supply when it's trying to charge the siren battery, Common fault on earlier models .
Especially if you say somethings wake up momentarily.

[Missing Lincs]

Originally Posted by harveys

Try unplugging the alarm siren unit incase it's shorting out the UEM supply when it's trying to charge the siren battery, Common fault on earlier models .
Especially if you say somethings wake up momentarily.

I second that, alarm fault causes weird things to happen with the UEM.

[Ummi60]

Okay. So now im wondering if this is the alarm unit you guys suggested unplugging or is there another alarm unit in the car somewhere?

[harveys]

Originally Posted by Ummi60

Okay. So now im wondering if this is the alarm unit you guys suggested unplugging or is there another alarm unit in the car somewhere?

No not the sensor but the siren unit.

https://www.volvoforums.org.uk/showp...64&postcount=1

Just unplug it and clear the codes and see what happens.

[SwissXC90]

Originally Posted by Ummi60

Okay. So now im wondering if this is the alarm unit you guys suggested unplugging or is there another alarm unit in the car somewhere?

The alarm logic and function is part of the REM in the boot of he vehicle.
What you had in your hands is just the interior movement t sensor
The alarm uses various sensors: switches in each door latch, trunk latch and bonnet latch. Movement sensors. And a siren unit.

The siren unit gets power and communicates via the UEM.
The siren contains an internal rechargeable battery and this often fails at around 10 years of age.
As the siren is connected to the UEM, it can cause weird effects when the battery charging circuits overload he UEM and the UEM data connections.