Boom Rest Proximity Switch Inconsistent State

Common Symptoms

• Platform display shows 99.01 and machine drive speed is reduced or cut to creep
• Boom will not telescope or lift even though it appears fully stowed in the cradle
• Machine drives at slow speed only and will not switch to full travel speed
• GCON controller LCD shows fault code 99.01 at the platform panel
• Boom functions may be locked out at ground controls with the fault active
• Machine appears stowed and cradle looks correct but the controller disagrees
• Fault clears sometimes on power cycle then returns after driving over rough ground

Probable Causes (Ranked by Likelihood)

• Stowed proximity switch is out of adjustment and not reliably detecting the boom in the rest position Very Likely
• Proximity switch has failed internally and sends intermittent or no signal to GCON Very Likely
• Wiring harness to the stowed proximity switch is chafed, corroded, or has a broken pin at the connector Likely
• Boom cradle or rest pad is worn or damaged so the boom does not sit close enough to trigger the switch Likely
• Moisture or debris has contaminated the proximity switch face and is affecting the sensing range Possible
• GCON controller has a corrupted input assignment or firmware issue causing a false fault read Less Likely

Step-by-Step Diagnostic Procedure

1. Step 1. Power the machine OFF at the ground controls, then power it back ON. Watch the GCON LCD on the platform. If 99.01 clears on restart but returns during operation, suspect a marginal gap on the proximity switch before anything else.

2. Step 2. Visually locate the stowed proximity switch. On S-series and Z-series booms it is mounted on or near the boom rest cradle at the turntable. Look for a cylindrical inductive sensor, usually M12 or M18 barrel style, threaded into a steel bracket. Check that the bracket has not been bent by a contact or tie-down strap.

3. Step 3. With the boom fully lowered into the cradle, measure the air gap between the face of the proximity switch and the boom tube or rest pad target. Genie spec for most inductive stowed sensors is 3 mm to 8 mm. If the gap is outside that range, loosen the locknut and adjust the sensor depth until the gap is 4 mm to 6 mm, then retighten.

4. Step 4. With the key ON and the boom resting in the cradle, use a multimeter set to DC Volts and probe the signal wire at the sensor connector. A healthy NPN proximity switch should read near 0 V when the boom is detected (sensor active) and pull up to supply voltage (10 V to 12 V DC) when the boom is removed. A PNP type reads high when active. Confirm the type on the sensor body label before interpreting results.

5. Step 5. Check supply voltage to the sensor. Probe between the power wire and ground wire at the connector with the key ON. You should see 10 V to 13 V DC. Low or missing supply voltage points to a wiring or fuse problem upstream, not a bad sensor.

6. Step 6. Inspect the full harness run from the sensor back to the GCON controller junction. Pay attention to flex points near the turntable, any cable wrap, and the connector pins at both ends. Unplug the connector and look for green corrosion, pushed-back pins, or water in the cavity. Clean contacts with electrical contact cleaner and reseat the connector.

7. Step 7. If the sensor reads correctly at the connector but 99.01 still shows on the GCON LCD, connect the Genie Service Tool laptop software via the J1939 port at the ground controls. Navigate to the input status screen and verify the GCON is receiving the correct stowed signal state. If the software shows the input toggling correctly but the fault persists, the controller input channel may need recalibration or a firmware update. That step requires Genie Service Tool and Genie dealer support.

8. Step 8. If adjustment and wiring checks do not resolve the fault, replace the proximity switch with a Genie-spec replacement part. After replacement, re-check the gap, cycle power, and verify the fault clears on the GCON LCD before returning the machine to service.

Frequently Asked Questions