2001 Lincoln Navigator Rear Suspension Dropped

After a long period of time hearing something that sounded like a noisy pump of some kind, the back of the Navigator has dropped to the bottom of the shocks.

I no longer hear the sound.

I'm guessing the pump died and I'm hoping it is a reasonable repair.

I borrowed a code reader from my brother, but it only showed code P1131

"HEATED OXYGEN SENSOR (HO2S) MONITOR - HO2S LACK OF SWITCHING
Diagnostic Trouble Code Description Possible Causes
P1131 -Lack of HO2S-11 Switch, Indicates Lean When an HO2S sensor indicates lean at the end of a test, the system is trying to correct for an over-lean condition. The code is set when the fuel control system no longer detects switching for a calibrated amount of time. See Possible Causes for DTC P1130"

I'm also guessing that OBDII code P1131 is not related and will be another problem I have to fix.

Can you give me some idea of the parts that need to be replaced?

I've done a log of "backyard mechanicing", but mostly 20+ years ago.

Thank you!