John Deere Engines SPN29FMI4 Fault Code: Secondary Analog Throttle Signal Out of Range Low
Also called Secondary Throttle Signal Out of Range Low, Throttle #2 Signal Out of Range Low, Throttle Voltage Low
Secondary Analog Throttle Signal Out of Range Low · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 29 FMI 4 means the ECU sees the secondary analog throttle signal reading lower than what is physically possible, below the throttle's low voltage specification. The engine will drop throttle to 0% until the fault clears and, depending on the configured recovery mode, may need the throttle returned to idle or the ECU power cycled before normal operation resumes.
Medium severity. This is logged as a Warning-level alarm, not an immediate shutdown code. The engine keeps running but throttle response is disabled or forced to idle until the condition clears, which can stop productive work and, in Resume Recovery mode, cause sudden engine speed changes when the fault comes and goes. Treat it as a same-shift diagnosis item, sooner if the machine is needed for lifting, travel, or PTO work that depends on stable throttle control.
What does John Deere Engines error code SPN29FMI4 mean?
SPN 29 FMI 4 is set on John Deere engine control units when the secondary analog throttle signal voltage coming into the ECU corresponds to a throttle position that is lower than the sensor or throttle can physically produce. In plain terms, the ECU is being told the throttle is somewhere below its real minimum, which tells the control system something in the signal path is broken rather than the operator actually calling for less throttle.
This code applies specifically to the secondary throttle channel, separate from the primary throttle circuit. Many OEM installations use two throttle inputs for redundancy or specific control schemes, and this fault means the backup or secondary channel is reading incorrectly low.
On OEM installations, the secondary analog throttle is set up on the ECU's Trim page. If that configuration is wrong, it can itself cause this fault code even when the wiring and sensor are fine, so configuration is worth checking alongside the physical circuit.
Common causes of SPN29FMI4
- Bad or corroded terminals or connector at the secondary analog throttle sensor
- Open, short, or high resistance in the return or supply wires feeding the throttle circuit
- Bad secondary analog throttle sensor or throttle device itself
- Open or shorted harness between the sensor and the ECU
- Short to the signal wire within the harness
- Mispin in the harness connector
- Bad terminals or connector at the ECU
- Bad ECU software
- Bad ECU
How to troubleshoot John Deere Engines SPN29FMI4: first checks
- With the ignition on and the fault active, check the secondary analog throttle connector and terminals for corrosion, looseness, or damage before doing anything else.
- Inspect the harness between the throttle sensor and the ECU for chafing, pinched wiring, or exposed conductors that could cause a short or open in the supply or return wires.
- Check for a mispinned connector or a signal wire shorted to another wire in the harness, since either can pull the signal below the valid low threshold.
- Verify the ECU's Trim page configuration for the secondary analog throttle on OEM applications. Incorrect trim setup can generate this fault even with good wiring.
- Check ECU connector terminals and connections for corrosion or poor seating, and confirm ECU software is current since bad ECU software is a listed possible cause.
- If wiring, connector, sensor, and configuration all check out, suspect the ECU itself as the last item on the list.
How the code clears
No separate clearing step is listed beyond restoring a valid signal. How the engine returns to normal throttle operation depends on which control unit response is configured: in Idle Recovery (the default), the operator must return the throttle to the low idle position (0% throttle) once the signal becomes valid again. In Resume Recovery, normal throttle operation resumes automatically as soon as the out-of-range condition clears, which can cause large changes in engine speed if the fault is intermittent. In Locked Recovery, normal throttle operation only resumes once the signal is valid again and power has been cycled on the ECU.
Frequently asked questions
What does SPN 29 FMI 4 mean on a John Deere engine?
It means the ECU has detected that the secondary analog throttle signal voltage is lower than what is physically possible, below the throttle's low voltage specification. The ECU treats this as an invalid signal and forces the throttle to 0% until the issue clears.
Will the engine shut down when this code sets?
No, this is logged as a Warning-level alarm, not a shutdown fault. The engine keeps running, but throttle control is forced to 0% and stays limited until the signal becomes valid again, and depending on the configured recovery mode, further operator action or an ECU power cycle may be required.
Why does my machine need the throttle returned to idle after this fault clears?
That behavior is specific to Idle Recovery mode, which is the default control unit response. Once the signal becomes valid again, the operator must move the throttle back to the low idle position (0% throttle) before normal throttle operation resumes.
Can bad ECU configuration cause this code even if the wiring is fine?
Yes. On OEM applications the secondary analog throttle is configured on the ECU's Trim page, and if that trim configuration is incorrect it can trigger this fault code independent of any wiring or sensor problem.
What's the difference between SPN 29 FMI 4 and SPN 29 FMI 3?
Both codes are part of the same troubleshooting sequence for the secondary analog throttle circuit, and both relate to signal voltage being out of range. FMI 4 specifically points to the signal reading too low, while a different FMI value on the same SPN points to a different type of out-of-range condition. They should be diagnosed together following the listed troubleshooting sequence.
Is this the same as a primary throttle fault?
No. This code is on the secondary analog throttle channel only. Many installations run a separate primary throttle circuit, and issues there would set different codes, such as those referenced under SPN 3513 in the same troubleshooting sequence.
What should I check first if this code keeps coming back intermittently?
Focus on the connector and harness first: loose or corroded terminals, chafed wiring, and mispinned or shorted connectors are common causes of intermittent low-signal faults. If the machine is set to Resume Recovery mode, be aware that an intermittent fault can cause sudden engine speed jumps as the condition clears and reappears.