John Deere Engines SPN29FMI3 Fault Code: Secondary Analog Throttle Signal Out of Range High
Also called Secondary Throttle Signal Out of Range High, Throttle #2 Signal Out of Range High, Throttle Voltage High
Secondary Analog Throttle Signal Out of Range High · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN29FMI3 sets when the secondary analog throttle signal voltage to the ECU is higher than what is physically possible for the throttle sensor, meaning the ECU sees a throttle position that can't exist. The engine responds with a warning alarm and forces the throttle to 0% until the signal is valid again, and depending on the configured recovery mode, may require the operator to return the throttle to idle or cycle power before normal control resumes.
Medium severity. This is logged as a Warning alarm, not a shutdown code, but losing normal throttle response can affect machine control and productivity. It should be diagnosed promptly, especially before returning to full working duty.
What does John Deere Engines error code SPN29FMI3 mean?
SPN29FMI3 means the ECU is reading a secondary analog throttle signal voltage that corresponds to a throttle position greater than what is physically possible for that sensor. In plain terms, the wiring or sensor is telling the computer the throttle is pushed further than it can actually go.
This is an electrical signal fault, not necessarily an engine performance fault. The ECU treats it as a safety concern because it can't trust an out-of-range throttle signal, so it takes control away from the operator's input until the signal returns to a valid range.
On OEM applications, the secondary analog throttle is configured in the ECU on the Trim page. If that configuration is wrong, it can itself generate this fault even if the wiring and sensor are fine.
Common causes of SPN29FMI3
- Bad terminals or connector at the secondary analog throttle sensor
- Open or shorted harness, including an open in the return wire
- Bad secondary analog throttle sensor (bad throttle)
- Bad terminals or connector at the ECU, or a bad ECU connector connection
- Mispin in the harness
- Bad ECU software
- Bad ECU
How to troubleshoot John Deere Engines SPN29FMI3: first checks
- Turn the ignition on and confirm the fault is currently active, since this code only displays under that condition.
- Inspect the secondary analog throttle connector and terminals for corrosion, looseness, or damage.
- Check the wiring harness for opens or shorts, paying particular attention to the return wire.
- Inspect the ECU connector and its terminals for a poor connection.
- Verify the ECU's Trim page configuration for the secondary analog throttle is set correctly, since misconfiguration alone can cause this fault.
- If wiring, connectors, and configuration all check out, test or swap the secondary throttle sensor itself before suspecting the ECU or its software.
How the code clears
No separate clearing step is listed beyond restoring a valid throttle signal. Depending on which control unit response is configured, the operator may need to return the throttle to the low idle (0%) position after the signal becomes valid (Idle Recovery, the default), or the throttle may resume normal operation automatically once the signal is valid (Resume Recovery), or the operator may need to cycle power to the ECU after the signal is valid again (Locked Recovery). No reset procedure beyond this recovery behavior is listed for this code.
Frequently asked questions
What does SPN 29 FMI 3 mean on a John Deere engine?
It means the secondary analog throttle signal voltage reaching the ECU is higher than what is physically possible, so the throttle high voltage specification has been exceeded. The ECU can't trust that signal and reacts by forcing the throttle to 0%.
Will SPN29FMI3 shut down my engine?
No, it's logged as a Warning alarm. It won't shut the engine down, but it does force throttle to 0% and can prevent normal throttle response until the fault clears, which affects how the machine drives or works.
Why does my throttle not respond after this fault?
Because the ECU's control unit response forces throttle to 0% when the out-of-range condition is detected. Depending on the configured recovery mode, you may need to bring the throttle back to idle, wait for the signal to become valid, or cycle power to the ECU before normal control returns.
Can a bad configuration cause this code even if the sensor is fine?
Yes. On OEM applications the secondary analog throttle is configured in the ECU's Trim page, and incorrect configuration there can cause this fault even with good wiring and a good sensor.
What parts should I inspect first for this code?
Start with the secondary analog throttle connector and terminals, the return wire and harness for opens or shorts, and the ECU connector. These are the most common physical causes listed before moving on to the sensor or ECU itself.
Is it safe to keep operating with this fault active?
Since throttle is forced to 0% and normal response may be delayed or locked out until the signal is valid, it's best to stop and diagnose the fault rather than continue working, since unpredictable throttle behavior is a safety concern.