Expression pedal suddenly doesn’t work

Maybe check the pedal settings/calibration and the automatic calibration settings in the SPACE system settings…
Check the behavior of the expression pedal output… Does it vary the parameter 0-100% neatly?
Also an ohm-meter (multimeter) will tell you the resistance behavior if you want a sanity check to compare pots, tapers, etc. and whether the resistance track is behaving erratically… which doesn’t seem to be your problem. For example, the Ernie Ball VP Jr varies resistance from 0 ohms heel position (shorted to ground) to 25Kohms resistance when in the toe position.  For your information, I believe the M-Audio EXP is 10K linear pot.

SYSTEM SETTINGS …

[UTILITY] —> [PEDAL CAL]
Select OFF to disable automatic Expression Pedal calibration

Here’s for the SPACE, p.26 U.M.:

Because different pedals can have different electrical characteristics, it is a good idea to “calibrate” your Stompbox to match the pedal. This can be done automatically, either all the time, or only when wanted. To turn calibration On/Off:
1) Press and hold the Encoder and Right Footswitch simultaneously for a few seconds to enter System Mode. Release the Encoder.
2) Turn the Encoder until [UTILITY] is displayed.
3) Momentarily press the Encoder.
4) Turn the Encoder until [PEDAL CAL] is displayed.
5) Momentarily press the Encoder.
6) Turn the Encoder to select either ON or OFF.
7) Press and hold the Encoder and Right Footswitch simultaneously for a few seconds to exit System Mode.
When Calibration is ON, the unit will remember the highest and lowest values it sees and will use these as pedal up and pedal down. Typically you will turn it ON, move the pedal between its maximum and minimum values a few times, then turn it OFF. Be aware that some pedals can be a bit quirky and pressing hard and pressing gently may give different values. For this reason we suggest turning calibration OFF when you’re happy with the setting. When Calibration is OFF, the values will be remembered and will not be changed by moving the pedal.
The Expression Pedal settings can be adjusted simply by pressing the Pedal to the full heel or full toe position and turning the Control Knobs. You’ll notice afterwards that whenever you move the Pedal, the green “Edited” LED in the upper right corner blinks. This indicates that Pedal programming is “live.” To program, press the heel completely down and adjust the knobs to get the sound that you want for the heel down position. You must turn the knobs to create the assignment. Knobs that are not turned are not assigned. Now, press the toe completely down and change the settings of any or all of the knobs. Parameters associated with any knobs that are moved will be mapped to the Pedal. Now, when you rock the pedal back and forth, you’ll hear the sound change between the two settings. After a few seconds of pedal and knob inactivity, the green “Edited” LED will stop flashing.
When the LED is solidly lit, you can turn any of the Parameter Control Knobs to change the sound without changing the Expression Pedal mapping.
When the Expression Pedal is used, the Billboard will display the changing value. If the Expression Pedal has been set up to control a single parameter, the display will show the parameter name and value in the same way as if you were turning the Control Knob. If the Expression Pedal has been set up to control multiple parameters, the display is a graphic representation of the Control Knobs. Control Knobs that are controlled by the Expression Pedal are represented as circles while unassigned Control Knobs are indicated by a solid line (dash). The 2nd character from the left indicates the position of the Expression Pedal with a value from 0-9 (0 = heel, 9 = toe).

Also, you were asking on the SPACE, according to U.M. p.56

1/4″ EXP jack is TIP_SLEEVE (TS “mono”)
1/4″ AUX jack IS TIP_RING_SLEEVE (TRS “stereo”)

If the actual jack is bad, it should not be too hard to fix…
I’ve also heard of contact/buggy issues fixed w re-seating the ribbon cables but am not sure if this would have anything to do w your problem…

And just because you asked… (UM p.54)

Restoring Factory System Settings
To restore System settings, power up while simultaneously pressing the Right Footswitch and the Encoder until [CLEAR SETUP] is displayed.

Restoring Factory Presets and System Settings CAUTION: This function will overwrite any Presets that you have saved.
To restore Factory Presets and all System settings, power up while simultaneously pressing the Middle Footswitch and the Encoder until [INITIALIZING] is displayed.

Generally, VP Jr (25K) or the Mission Engineering are the ones recommended. In the past I’ve used several but prefer the VP Jr because the string design keeps any position extremely stable and doesn’t “wiggle” the parameter. I’m currently using a VP Jr on another pedal and much of the throw is towards the “toe 1/3rd” end, so this may be normal. Not sure if you are expecting perfection.

Any tech should be able to diagnose whether its the proper behavior. Then you could send it in to support if there is an actual issue.
If expression works with the VP Jr. it is almost certainly not the SPACE, generally expression pedals with range adjustment etc are more prone to not being set up correctly.

My best guess is this:
TRS-to-TS adapter connects the signal equally between the tip and the ring… This way the ring (R) is not FLOATING inside the SPACE exp jack… (which is likely how the SPACE EXP jack handles a ring connection) Instead, it allows the ring to conduct thru the TIP (T) of the adapter for the SPACE to read properly.

If all of this is indeed correct (I dont have one in front of me to test), then cutting and re-wiring a new TS jack to the M-audio would also work.
The wires connected and soldered together as T+R–TIP and keeping S as SLEEVE/GROUND

EDIT: In electronic terms, this converts it from a voltage divider to a variable resistor (“rheostat” config). The Ernie Ball VP Jr is wired as a 25K variable resistor. I just checked.