Drive Cutout Active, Platform Motion Blocked

Common Symptoms

• Platform LCD on the upper control box shows code 31 and drive functions are disabled
• You can lift and lower the platform but the machine will not travel in any direction
• Drive joystick or thumb switch is unresponsive even though the machine powers on normally
• Alarm or indicator light on the upper control box is solid or flashing while drive is blocked
• Machine drives normally at ground level but cuts out when the platform is elevated above the slow-drive height threshold
• Pothole guard trips or hangs down and does not retract fully, blocking drive
• Machine displays code 31 after a tilt alarm has been cleared but before the tilt sensor resets

Probable Causes (Ranked by Likelihood)

• Platform elevated above slow-drive height threshold without slow-drive bypass engaged, so the controller has cut drive as designed Very Likely
• Tilt sensor (deck tilt switch or pendulum sensor) is tripped or stuck in a fault state, signaling an out-of-level condition Very Likely
• Pothole guard (front or rear) not fully retracted or limit switch not reading guard in the home position Likely
• Height limit switch or proximity sensor out of calibration or failed, causing the controller to see the platform as elevated when it is not Likely
• Faulty or corroded wiring/connector between the tilt sensor, pothole guard switch, or height switch and the GCON or TCON module Possible
• Slow-drive bypass switch on the ground control box is damaged, stuck, or wired open so the controller never receives the bypass signal Possible
• GCON or TCON controller internal fault latching code 31 due to a prior tilt or drive fault that was not properly cleared Less Likely

Step-by-Step Diagnostic Procedure

1. Step 1. Fully lower the platform to ground level and check whether code 31 clears on the Platform LCD. If it clears immediately, the machine is functioning as designed. The slow-drive height cutout is active above the set threshold and drive will only resume at speed when the platform is lowered, or when the slow-drive bypass is held at the ground controls.

2. Step 2. With the platform fully lowered and code 31 still active, walk around the machine and inspect both pothole guards (front and rear). Push each guard up by hand to confirm it moves freely and seats flush. Look for bent brackets, mud, or debris jamming the guard in the lowered position.

3. Step 3. Locate the pothole guard limit switches (usually small roller-arm or plunger switches mounted on the scissor frame near each guard). With the guard fully up, the switch plunger should be fully depressed. Use a multimeter set to continuity or DC voltage to confirm the switch closes when the guard is home. No continuity with the guard seated means a failed or misaligned switch.

4. Step 4. Check the tilt sensor. On most SJIII and RT models the tilt sensor is a small mercury or pendulum switch mounted on the platform deck or scissor frame. With the machine on a flat, level surface, confirm the machine is not on a grade. Measure DC voltage at the tilt switch signal wire at the GCON connector. A stuck or failed tilt switch will read an out-of-tolerance signal even on flat ground. Consult the wiring diagram for the expected voltage window (typically 0 V or battery voltage depending on switch type).

5. Step 5. Inspect the height limit switch or proximity sensor on the scissor stack. This switch tells the controller whether the platform is above the slow-drive cutout height. Check the target gap on proximity sensors. The spec is typically 3-5 mm between the sensor face and the actuating bracket. Re-gap or clean the sensor face if needed. Check for bent or missing actuator brackets.

6. Step 6. Inspect all wiring harness connectors going to the GCON and TCON modules. Look for spread pins, corrosion (especially on outdoor RT models), or chafed insulation. Unplug, inspect, apply dielectric grease, and reseat each connector. A corroded ground or signal pin on the tilt or height switch circuit is a common field fix.

7. Step 7. If you have access to a Skyjack diagnostic harness via the EZcal / Pcal handheld, connect it and review the live input status screen. You can see in real time whether the tilt, height, and pothole guard inputs are reading correctly without replacing parts. This pinpoints the faulting input before you start swapping sensors.

8. Step 8. If all switches, sensors, and wiring check out and code 31 will not clear, cycle full power off and back on at the ground controls. If the code returns immediately with the platform on level ground and guards home, the GCON or TCON module may be latching an internal fault. At this point you need a Skyjack service dealer to perform a controller reset or module replacement. Do not attempt to bypass the drive cutout circuit in the field.

Frequently Asked Questions