Cadillac Seville / Cadillac Eldorado Forum Discussion, 2001 SLS Lumbar adjustment troubleshooting in Past Cadillac Vehicle Discussion; Where can I find some info on troubleshooting the drivers side lunbar adjustment circuitry??
The switch does nothing, not up ...
Start with the switch.
I guess form your post the other seat controls work fine so MSM gets power.
There are 2 motors actuating the lumbar movements:
Vertical and horizontal (in/out).
Each motor has a sensor (variable resistor ~10KOhm = potentiometer) and as the motor moves the sensor resistance varies from ~100Ohm to ~10KOhm.
Even with the sensors disconnected (or malfunctioning) the movement should still happen as long as you use the buttons (but memory feature may not work correctly). You should have MSM codes if the sensors are problematic.
So you have 5 wires to the lumbar switch (supply and 4 returns up/down/in/out) and these are all connected to the MSM (located underneath the seat. Then form the MSM you have a 10 wire harness going to the lumbar adjustments (2x2 wires for the motor power and 2x3 wires for the sensors).
Either the harness going to the lumbar motors is having an issue or the lumbar adjustment switch or the harness to it has an issue.