Pneumatics Won't Fire: A Full Diagnostic Tree

Symptom

You command a piston and nothing moves. Pneumatics failures are almost always systematic; walk this tree top to bottom and do not skip steps.

1. CAN ID 0 (the #1 mistake)

The power distribution device and the legacy CTRE PCM should be configured so the FRC libraries can find them. As FRC Zero’s troubleshooting guide states emphatically: the PDP and PCM should ALWAYS have the same CAN ID of 0 , because FRC libraries assume this. A wrong CAN ID makes a perfectly wired module invisible. (The REV Pneumatic Hub is addressed separately by its own CAN ID; match what your code expects.)

2. Is the robot actually enabled and the module told to run?

• Confirm the Robot Status Light shows enabled (Teleop/Test), not just connected.

• The compressor must be enabled. With the modern WPILib API, closed-loop control is already running by default the moment you construct a Solenoid/DoubleSolenoid — most teams never need to touch the Compressor class at all. Only instantiate a Compressor object if you want explicit status/telemetry or to pick a mode yourself with enableDigital(), enableAnalog(), or enableHybrid(); simply constructing the Compressor object does not by itself start closed-loop control.

• Instantiate solenoids with the right module type:

  // CTRE PCM Solenoid intake = new Solenoid(PneumaticsModuleType.CTREPCM, 1); // REV Pneumatic Hub DoubleSolenoid claw = new DoubleSolenoid( PneumaticsModuleType.REVPH, 0, 1);

Using the wrong PneumaticsModuleType is a silent no-op.

3. Power and fuses

The PCM/PH and VRM are powered from the power distribution device. Check the fuse/breaker feeding the module. A blown fuse = dead module.

4. Air pressure

• High side should reach the system max (the legal ceiling is 120 PSI); the regulated low side typically reads ~60 PSI to the cylinders.
• If low side reads 0, the regulator is backwards or set to zero.
• If high side reads 0, a manual vent valve is open or the compressor isn’t charging.

5. Double-solenoid logic

A double solenoid driven by two separate, conflicting commands will fire asynchronously or chatter. Drive it with a single set(kForward/kReverse) call and matching tubing lengths/fittings on both ports.

6. Leaks

If the compressor runs continuously and pressure won’t hold, you have a leak. Spray a small amount of soapy water on every fitting; bubbles reveal the leak. A stuck pressure switch can also run the compressor forever, check it.

7. Sticky faults

Clear PCM/PH sticky faults in Phoenix Tuner / REV Hardware Client self-test, then verify CAN wiring. Persistent faults after clearing point to a real wiring or firmware problem, update firmware.

The discipline

Change one thing, retest, then move on. The fastest pneumatics debuggers don’t guess; they walk the tree.

Key takeaways

• The single most common pneumatics bug is a wrong CAN ID, the PDP and legacy CTRE PCM should both be CAN ID 0.
• Enable the compressor in code (construct a Compressor / enableDigital()) and instantiate solenoids with the correct PneumaticsModuleType (CTREPCM vs REVPH).
• A continuously running compressor that won’t hold pressure means a leak (soapy-water test) or a stuck pressure switch.

This lesson was adapted from learnfrc.com.