taillight problems

all2many · Post by **all2many** » 07 Jan 2018, 17:36

Weird?? Taillights work fine as long as you do not start or turn ignition to start position. Lights go on once I turn to start the car than lights go out when started ? Brake , backup , turn & hazard still work but taillights go out. Any idea where to look? Have checked fuses good there.

Post by **abscate** » 08 Jan 2018, 05:29

Check grounds, but lights on P2 are all controlled by modules rather than analog wiring.

The fast way to get. This done is connecting VIDA and diagnosing there

all2many · Post by **all2many** » 08 Jan 2018, 19:22

Yeah wish my VIDA would work. Not many Volvo's in Fla . and finding someone to read it is a problem. Just noticed the front and rear fogs go out also once started. Think last time I had Vida working something about high light something came up, but did not notice this problem at that time. Mention where the ground would be and how to check REM? that might help as I am new to servicing Volvo;s (but learning}

Post by **mrbrian200** » 08 Jan 2018, 22:02

If the lamps in question come on before starting the engine I'm inclined to suspect the wiring/grounds are probably ok.

After starting the vehicle, does anything happen when you turn the light switch between Off/park/ON?

all2many · Post by **all2many** » 09 Jan 2018, 06:34

Light switch has no effect on problem. looked at a wiring diagram noticed REM has a like crossover circuit looks like when you start it opens switch to that circuit. Wish my VIDA would work---- In fla. Volvo dealers are few and charge $$$ just to look at it . Indie shops have little knowledge as it is not popular car here. Sent off for new VIDA guess wait and see if that works. Thanks for reply

Post by **mrbrian200** » 09 Jan 2018, 09:32

Even with vida I suspect this might be a tricky one to diagnose unless VIDA displays a specific DTC , such as for the light switch module or the solar/twilight sensor. The lights come on only before the car is started may be how the software coded as a functional test to catch burned out bulbs before starting the car. Once the car is started the CEM powers the lights based on input factors (LSM, solar sensor, etc). I'm just brainstorming here. Getting to the bottom of this may depend on understanding how the CEM software is coded to handle various inputs under different conditions (KOEO/start/run), which I wouldn't doubt a number of dealer techs wouldn't fully understand. Trial and error problem resolution is usually cost prohibitive at a dealer because they charge you by the hour, plus parts, regardless whether they fully/functionally understand the systems they are working on or not.