Headlight Switch Module Not Working, DIM is dark, and radio is dark. Why? Help! Topic is solved

[mrbrian200]

Just to clarify, my thumbwheel nor any other part of my lsm works. Most of my dash lights went dim, radio display out, bright headlights won't stay on etc. Other people who posted similar symptoms said they had some success by changing the lsm.

If all the functions controlled by the steering wheel module work: turn signals.. wipers.. switching the text display modes on the DIM.. everything except high beam function, the fuse would be ok and yes most likely the LSM puked out.

[Daveliz99]

Thank you very much mrbrian200. That's good news, and i'll go get one asap and post again if it works or not.

[JohnnyBee323]

Fixed it. It was the light switch module. $30 part and 30 second installation, and done. Thanks everyone.

[ionianp2]

I know this is a slightly old thread but this happened to me last night (exact same symptoms!) and while researching I stumbled upon this thread. I wanted to share with you folks a fix.

I took out the LSM, cracked it open and saw no visual damage/cracks on the soldering. I ended up taking a heat gun to the circuit board on the low setting to the point where the solder became shiny and fresh. I plugged it back in and voila! Worked like a charm!

I also painted the solder connections with a clear coat pen to replace the melted corrosion protection. Even my wife who is an electrical engineer and meticulously looked at the board was pleasantly surprised.

Takeaway: before buying another used module off of someplace, you have nothing to lose take a heat gun to the soldered connections.

[mikahack]

Hi ionianp2,
Please, can you explain, where exactly you heat with heat gun.
Please see attached pictures.
Thank you in advance.

[Stu70]

Have a read of this ….

https://h24-files.s3.amazonaws.com/3479 ... -QPJPa.pdf

[firstv70volvo]

Have a read of this ….

https://h24-files.s3.amazonaws.com/3479 ... -QPJPa.pdf

I had a bad solder joint on the light switch module (LSM) circuit board and tried reflowing the solder joints in the area suggested in the pdf but no luck. After reflowing the solder joints for almost every joint/pin on the board I did finally repair the board. The last group of pins where I reflowed the solder and fixed the board was the microcontroller IC with 44 pins and some other 5V solder joints. At first, I attempted to troubleshoot the problem to better pinpoint the problem area and the problem seemed to trace back to the microcontroller, which controls transistors that switch on power to the LSM back light bulbs, they weren't working. Not sure if was a bad solder joint on the microcontroller pins or 5V power to this device though. During troubleshooting I did label everything I could identify while tracing connections from device to device, which may help anyone else willing to spend the time to repair this board. New LSM cost ~$200, salvage yards should be much cheaper if you can find the right one for your car. I choose to repair the board because it had an obvious solder joint problem, I could put pressure on the instrument lighting knob/wheel and everything would start working again.

labeling notes, no guarantee all of this is correct

volvo light switch module circuit board top side view with labeling.jpg (250.77 KiB) Viewed 2341 times

pdf with more photos and labeling and same no guarantee all is correct
https://app.box.com/s/oywntibtpneny4clu2ndw9o72kjh7m91