If your lumbar and bolster support system has stopped working with the Ultima seats that came with the Trans AM GTA , chances are the valve assembly is the culprit. Here's how I fixed mine for under €10 with cheap new parts.

Symptoms:

• Pump runs fine, but the air bladders for the side bolster and lumbar doesn't inflate.
• Bladders inflated when connected directly to the air pump bypassing the valve block.
• Valve block clicks when buttons are pressed but nothing happens

Root cause: The original valve block contains small solenoid valves that after 35+ years that propaply have hardened seals, both driver and passenger side didn't work for me. I tried cleaning them and blowing with compressed air, but with no luck.

The fix: Replace the valve assembly with two generic 12V (normally closed) mini solenoid valves from AliExpress per seat. It's important that the solenoids are normally closed, not normally open. Below the ones I bought for under 4€ a piece.
https://www.aliexpress.com/item/1005...7d6318022HYTmY

Wiring – drivers seat:
I cut the wires from the original connector pictured below. And wired in the solenoids this way.

• Lumbar solenoid + → BRN wire 763
• Bolster solenoid + → PPL wire 765
• Both solenoid − → BLK/WHT wire 769 (ground)

No rewiring needed anywhere else in the car. Original buttons work.


Air hoses: Add a T-fitting on the pump outlet and run a line to each solenoid inlet. Since you now have two solenoids instead of a single block valve assembly. The solenoid outlets then connect to the original bladder hoses.

Mounting: Zip tie the solenoids to the seat frame.


Total cost: about €10 and an hour of work. Not counting the troubleshooting, lol. I did it with the help of the original service manual and a bit of AI.


Hope this helps someone else avoid hunting for NOS parts! The valve block is no longer sold and a NOS part is not certain to work anyway.



Air pump pictured below, large black box. There is only one, runs both seats. It's under the drivers seat.
Old valve block
Two new solenoids
Air hoses


This is the connector you need to cut and rewire to the new solenoids. Black and white cable is common ground for both of them.





Proof of concept, tried it inside connected directly to a 12v battery.