JLG Scissor Lift 221 Fault Code: TPS 2 Signal Voltage Low
Also called Function Problem - Horn Permanently Select, Function Problem - Horn Permanently Selected
TPS 2 Signal Voltage Low · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 221 on JLG scissor lifts (M3369, M4069) means the horn switch in the platform control box was closed at power-up. JLG identifies this internally as SPN 51 / FMI 0. It is a startup interlock fault, not a wiring failure by default, and it usually clears once the switch is released.
Low severity. This code does not indicate machine damage or an unsafe operating condition by itself. It simply blocks normal function startup until the horn switch input is confirmed open. Treat it as an annoyance fault to resolve before use, not an emergency.
What does JLG Scissor Lift error code 221 mean?
Fault code 221 is JLG's way of flagging that the horn switch on the platform control box was already closed, or reading as closed, the moment the machine powered up in platform mode. Because the controller expects switches to be in a rest state at startup, a closed horn switch is treated as a fault condition rather than a normal horn request.
JLG's own help text is direct about this: 'Horn switch in platform control box closed at start up. Release switch to clear fault.' In other words, the machine is telling you that from its point of view, someone or something is holding the horn button down, or the switch itself is stuck, damaged, or wired in a way that makes it look permanently pressed.
This same fault code also appears in JLG's records tied to a description about TPS 2 signal voltage being low, but the detailed check procedure and help message both point specifically to the horn switch condition. For practical troubleshooting, focus on the horn switch and its wiring first.
Common causes of 221
- Horn switch physically stuck in the closed (pressed) position due to damage or wear
- Debris, dirt, or an obstruction jamming the switch so it cannot spring back open
- The switch cable or ribbon connector on the platform board shorted or pinched, making the input read as closed even though the physical switch is fine
- A faulty platform board that misreads the horn switch input as closed regardless of switch condition
How to troubleshoot JLG Scissor Lift 221: first checks
- Look at the horn switch itself for visible damage, sticking, or physical obstruction before touching any wiring
- Try cycling the switch by hand to see if it springs back freely, and clear away any dirt or debris around it
- Disconnect the horn switch ribbon cable at the platform board and see if the fault clears with the switch electrically isolated
- If the fault stays present with the ribbon cable disconnected, suspect the platform board rather than the switch or wiring
- If the fault clears once the ribbon cable is disconnected, the problem is in the horn switch or its wiring, not the board
How the code clears
JLG's help message states this fault clears simply by releasing the horn switch. If releasing the switch does not clear it, run the check procedure: disconnect the horn switch ribbon cable on the platform board. If the fault code is still present with the cable disconnected, replace the platform board. If the fault code goes away once the cable is disconnected, replace the horn switch or the platform board as needed. No separate reset procedure is listed for this code.
Affected models and serial ranges
221 appears in our records across 2 JLG Scissor Lift models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| M3369 | Serial range not listed in source records |
| M4069 | Serial range not listed in source records |
Frequently asked questions
What does JLG fault code 221 mean?
It means the horn switch in the platform control box was closed, or read as closed, at power-up in platform mode. JLG labels it a function problem, horn permanently selected.
How do I clear fault code 221 on a JLG scissor lift?
Release the horn switch. JLG states this clears the fault. If it does not clear, the switch may be stuck, damaged, or the wiring or platform board may need inspection and replacement.
Is fault code 221 dangerous to keep operating with?
No specific safety hazard is described for this code beyond blocking normal function startup. It is a low severity electrical interlock fault rather than a structural, hydraulic, or lifting risk.
Why does my JLG lift show fault 221 even though I'm not touching the horn button?
The horn switch may be physically stuck closed, jammed by debris, or its wiring or ribbon cable could be shorted so the controller sees it as pressed even when it is not.
What is the difference between the horn switch and the platform board causing this fault?
Disconnect the horn switch ribbon cable at the platform board. If the fault clears, the switch or its cable is at fault. If the fault remains with the cable disconnected, the platform board itself is likely faulty.
Does fault code 221 relate to the throttle position sensor (TPS)?
JLG's records list a TPS 2 signal voltage low description alongside this code number, but the detailed check procedure and clearing instructions are specific to the horn switch condition, so that should be your primary troubleshooting path.