TCS light on — air switch bad?

Not necessarily your problem, but either of the 2 pictured could be. Luckily for you they are the same part # from Volvo. Better to get diagnosed with Bendix Acom software first.

 

Mechanic didn't tell you whole truth.
TCS light could be on for many reasons.
Steering position sensor.
Yaw sensor
Valves electrical malfunction
Brake demand air pressure sensor.
There is tags attached to the sensors pigtails.
Two sensors for PRIMARY and SECONDARY. One sensor is for APPLIED BRAKE PRESSURE and one for rear airbags pressure to sense load. Manifold might be different from year to year but I believe right top one is for rear airbags.

 

Mechanic said...........
You need to know exactly code to figure out what is wrong.
Did you check Diagnostics menu/View active faults/ Brake ECU for any codes? Or you need to diagnose it with ACom for codes.

 

you would need to have some sort of bendix software to be able to get to the bottom of this most of the time there is a calibration sequence after you install these switches and there is a few air switches that could do it, like applied brake psi, suspension psi, applied trailer brake psi, and parking brake psi. that being said there is no real way to tell unless you have software replace all 4 and try calibration sequence and see if it goes off but you will spend the $$ $ in parts that way, you can buy 2 and alternate till light shuts off. but not really many other options besides this.