Kohler Aux Input Error: What It Means & How to Fix

What Is the Auxiliary Input?

The auxiliary input is an optional feature on Kohler 14RCA, 20RCA, 26RCA, and RCAL series generators with an RDC2 controller. It’s a digital input port designed to accept signals from customer-supplied equipment—things like remote switches, sensors, or a Programmable Interface Module (PIM). When properly configured, these devices can communicate status information or control signals to your generator’s control panel.

When the auxiliary input receives a signal that tells the generator to shut down, the RDC2 controller interprets that as a shutdown command and stops the unit. This is a safety feature: it prevents the generator from running when external equipment detects a problem.

Why Your Generator Shut Down

The Aux Input error means one of two things: either an external device is actively sending a shutdown signal, or a loose connection is causing the input to register as “closed” (activated). Common culprits include:

• A connected remote switch or sensor that was accidentally activated or is malfunctioning
• A Programmable Interface Module (PIM) that is sending a shutdown command
• Loose or corroded wiring at the auxiliary input terminals
• Water or moisture damage to the input connector or wiring
• A faulty external device that is stuck in the “on” position

If you didn’t intentionally install any external equipment on the auxiliary input, a loose wire or moisture intrusion is the most likely cause.

Diagnostic Checklist

1. Visually inspect the auxiliary input terminals on the RDC2 control panel. Look for loose wires, corrosion, or water damage. Tighten any loose connections with a small screwdriver. If you see white or blue-green corrosion, gently clean the terminals with a dry cloth or fine sandpaper.
2. Check for any external devices connected to the auxiliary input. Look at the control panel and trace any wires leading from the “Aux Input” or similar labeled terminals. If you find a switch, sensor, or module, verify it is in the correct position. Consult the device’s manual to confirm it should not be triggering a shutdown.
3. Inspect wiring for damage. Follow the auxiliary input wires from the control panel to any connected device. Look for cuts, pinches, water damage, or signs of rodent chewing. Moisture is especially common in outdoor installations or in damp basements.
4. Disconnect the auxiliary input temporarily. If you have a connected device, safely disconnect the wires from the auxiliary input terminals (consult your generator manual for the correct procedure). Attempt to restart the generator. If it starts and runs normally, the problem is with the external device or its wiring, not the generator itself.
5. Test the external device independently. If you disconnected a switch or sensor, test it outside the generator system to confirm it is functioning correctly. A stuck or shorted switch will need to be replaced.
6. Reconnect and verify proper operation. Once you’ve identified and fixed the problem (cleaned corrosion, replaced a faulty device, or repaired wiring), reconnect the auxiliary input and attempt a normal startup. The error should not reappear.
7. Check the generator manual for auxiliary input configuration. Some systems require specific wiring or settings to enable the auxiliary input. If it was recently installed, verify the installation matches the manual’s instructions.

When to Call a Pro

Stop troubleshooting and contact a Kohler-certified technician if:

• You see water inside the control panel or corrosion that won’t clean off easily
• The auxiliary input terminals are damaged or the connector is cracked
• You’ve disconnected all external devices and the error still appears
• You’re unsure how to safely disconnect wiring or access the control panel
• The external device (PIM, switch, or sensor) is damaged or you cannot identify what it is
• The generator still won’t start after you’ve cleared the error and restarted the system

A technician can test the RDC2 controller’s input circuits and determine whether the problem is a hardware fault or a configuration issue.

Parts You May Need

• Replacement auxiliary input connector or wiring harness (if damaged)
• Programmable Interface Module (PIM) replacement (if the original is faulty)
• Remote switch or sensor (if the connected device is broken)
• Dielectric grease (to protect terminals from corrosion)
• Wire connectors and electrical tape (for repair)

Frequently Asked Questions

What is a Programmable Interface Module (PIM)?

A PIM is an optional add-on device that connects to the auxiliary input and allows you to monitor or control your generator remotely or integrate it with other systems. If you don’t remember installing one, you probably don’t have one. Check your generator’s documentation or look for any unfamiliar boxes or modules near the control panel.

Can I just leave the auxiliary input disconnected?

Yes, if you don’t use any external equipment with your generator, you can safely leave the auxiliary input unconnected. The feature is entirely optional. However, make sure the wires are not left exposed or dangling where they could short against metal parts or get wet. If the wires are permanently installed, consult your manual or a technician about the proper way to disable or cap the input.

Why did this error suddenly appear if nothing changed?

Corrosion, moisture, or a loose connection can develop over time, especially in humid or outdoor environments. Vibration from the generator running can also loosen terminal connections. Even if nothing was intentionally changed, environmental factors may have triggered the auxiliary input to register as active.

Will the generator restart automatically after I fix the problem?

No. After you’ve resolved the issue, you must manually restart the generator. The RDC2 controller will not automatically resume operation once a shutdown error has occurred. This is a safety feature. Restart the unit using the normal start procedure outlined in your manual.

Disclaimer

This article provides general diagnostic information for Kohler generators with RDC2 controllers. Always refer to your specific generator’s owner manual and the manufacturer’s troubleshooting guide for detailed procedures and safety requirements. If you are unsure about any step, contact a qualified Kohler service technician or dealer. Improper diagnosis or repair can damage equipment or create safety hazards.

Source: Information adapted from official manufacturer documentation (reference). Always consult your generator owner’s manual for model-specific procedures.