Troubleshooting No Power Issues on the Tennant T5e / Nobles SS5 Floor Scrubber

If your Tennant T5e or Nobles SS5 floor scrubber is completely unresponsive—no power-up, no deck movement, and no battery indicator lights—you’re not alone. This is a common issue, but with a step-by-step diagnostic approach, it can usually be solved quickly. In this guide, we'll walk through what might be causing the issue and how to test and fix each component involved in powering the machine.

Common No-Power Scenario

Your T5e or SS5 is:

• Fully charged

• Not responding when the key is turned

• Has a deck stuck in the down position

• Not cycling the functions properly, despite pressing the green button

This can often be linked to issues with safety switches, relays, or the charger interlock.

1. Start With the Tank Safety Switch

A stuck or faulty tank safety switch can disable power flow to key functions. You can bypass this temporarily for testing:

• Bypass Method: Use a standard automotive fuse or small piece of conductive wire to close the circuit between the switch leads.

• Result: This removes the safety interlock, allowing the machine to engage the control board and power the deck.

⚠️ Note: Bypassing safety features should only be used temporarily for diagnostics.

2. Check Battery Pack Voltage

Use a voltmeter to verify you have over 21 volts at the battery terminals:

• Red to red, black to black = positive voltage

• If below 21V, recharge the batteries and recheck

If you don't have a voltmeter, plug the charger into the machine. The display will show current voltage before it starts charging.

3. Inspect Key Switch Functionality

• Remove the two wires from the key switch

• Use an ohmmeter (set to resistance /Ω mode)

• Insert the key and turn it: Resistance should drop to near 0

• If it doesn’t: Clean or replace the switch (cheap fix)

You can also bypass the key switch temporarily using a fuse to test circuit continuity.

4. Relay Checks: Circuit Relay 3 (CR3)

Relay CR3 controls the entire machine’s power-up function:

• Located near the front of the machine

• Swap with the adjacent vacuum relay (same specs)

• Disconnect one battery cable before removing relays

If the machine powers up after swapping, the relay is bad and should be replaced.

5. Charger Interlock Bypass & Testing

The onboard charger disables the machine while plugged in to prevent movement:

• Find two yellow wires running from the charger to the control board

• Disconnect them and test for continuity

• Should be closed (0 resistance) when NOT plugged in

• Should be open when charger IS plugged in

A faulty interlock prevents power flow to the relay and disables the machine.

6. Review the Schematic Diagram

The Tennant service manual includes detailed ladder diagrams for troubleshooting:

• Follows the flow of voltage from battery through relays and switches

• Helps isolate whether control board, key switch, or charger interlock is at fault

Use the diagram to trace each connection and verify electrical flow.

Final Diagnostic Checklist

Before replacing parts, run through this checklist:

•  Battery voltage > 21V

•  Battery terminals secure and clean

•  Key switch continuity tested or bypassed

•  Relay CR3 swapped/tested

•  Charger interlock tested for proper open/close state

•  Fuses and wiring connections intact

If all of the above are verified and the machine still won’t power on, contact PowerKleen for advanced support or replacement parts.

Conclusion

Power issues on the Tennant T5e and Nobles SS5 are common, but not unfixable. With basic tools like a voltmeter, ohmmeter, and some patience, you can narrow down the problem and get your machine back in service. Always start with safety switches and work your way through the system logically.

Need help? Contact us at powerkleen.net or call 859-484-8882 to talk with a specialist.