John Deere Engines SPN91FMI4 Fault Code: Primary Analog Throttle Signal Out of Range Low
Also called Primary Analog Throttle Signal Out of Range High, Primary Throttle Signal Out of Range Low, Throttle #1 Signal Out of Range Low, Throttle Voltage Low
Primary Analog Throttle Signal Out of Range Low · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 91 FMI 4 means the ECU sees the primary analog throttle signal voltage lower than what is physically possible for the throttle, below the throttle low voltage specification. The engine sets throttle to 0% until the signal becomes valid again and the recovery condition configured in the ECU is satisfied. This is logged as a Warning alarm level.
Medium severity. This is logged as a Warning, not a shutdown-level fault, but the ECU forces throttle to 0% when it's active, which can stop machine operation until the fault clears or is reset. Treat it as a stop-and-diagnose issue rather than an emergency, but don't ignore it since throttle response is directly affected.
What does John Deere Engines error code SPN91FMI4 mean?
SPN 91 FMI 4 is set when the ECU reads the primary analog throttle signal voltage as lower than the throttle low voltage specification, a level that doesn't correspond to any real, physical throttle position. In plain terms, the controller knows the wiring or sensor is telling it something that can't be true, so it stops trusting the throttle signal.
When this happens, the ECU immediately sets throttle output to 0%, no matter what the operator is actually asking for with the pedal or lever. How the engine recovers from there depends on which of three configured responses is active: Idle Recovery (the default, requiring the operator to return the throttle to 0% before normal control resumes once the signal is valid again), Resume Recovery (throttle picks back up automatically as soon as the signal clears, which can cause large, sudden jumps in engine speed if the fault is intermittent), or Locked Recovery (throttle stays at 0% until the signal is valid AND the ECU has been power cycled).
The fault is checked and can display any time the ignition is on and the fault condition is active. On OEM installations, this code can also be triggered or worsened by incorrect Trim page configuration in the ECU, since the throttle's low-end voltage range and mapping have to be configured correctly for the ECU to interpret the signal properly.
Common causes of SPN91FMI4
- Bad or corroded terminals, pins, or connector at the primary analog throttle sensor
- Open or high resistance in the throttle signal return wire
- Open or high resistance in the throttle signal supply wire
- Short to the signal wire somewhere in the harness
- Open circuit or mispin in the harness
- Bad primary analog throttle position sensor itself
- Bad or loose connector or pin connection at the ECU
- Bad ECU software
- Bad ECU
How to troubleshoot John Deere Engines SPN91FMI4: first checks
- Confirm the ignition is on and re-check whether the fault is currently active or stored as history, since this code only displays while active with ignition on
- Inspect the primary analog throttle connector and terminals for corrosion, looseness, bent pins, or moisture intrusion
- Check the throttle signal return and supply wires for opens or high resistance, and inspect the harness for chafe points or shorts to the signal wire
- Verify harness pinout at both the throttle sensor and the ECU connector to rule out a mispin
- On OEM-installed machines, verify the primary analog throttle Trim page configuration in the ECU is set correctly for this throttle
- Check ECU connector pins for corrosion or damage
- If wiring and connectors check good, test the throttle sensor itself for correct output across its range
- If all wiring and sensor checks pass, consider ECU software or ECU hardware as the remaining suspects
How the code clears
No separate clearing step is listed beyond the ECU's built-in recovery logic. Depending on which response mode is configured, the throttle either resumes automatically once the signal is valid and the operator returns to 0% throttle (Idle Recovery, the default), resumes immediately once the signal clears (Resume Recovery), or stays locked at 0% until the signal is valid again and the ECU has been power cycled (Locked Recovery). Fixing the underlying wiring, connector, sensor, or ECU issue is what actually resolves the fault; the recovery mode only governs how throttle behaves once the signal problem clears.
Frequently asked questions
What does SPN 91 FMI 4 mean on a John Deere engine?
It means the ECU is reading the primary analog throttle signal voltage as lower than the throttle low voltage specification, a value that doesn't match any physically possible throttle position. The ECU responds by forcing throttle output to 0% until the signal is valid again.
Why does my engine drop to idle or not respond to the throttle with this code active?
When this fault is active, the ECU sets throttle to 0% by design. Depending on the configured recovery mode (Idle Recovery, Resume Recovery, or Locked Recovery), normal throttle response only comes back after specific conditions are met, such as returning to 0% throttle, the signal clearing, or an ECU power cycle.
Can a bad connector really cause this code?
Yes. Bad terminals or a bad connector at the primary analog throttle sensor is listed as a possible cause across multiple versions of this diagnostic, along with opens, shorts, or high resistance in the harness wiring.
Is SPN 91 FMI 4 something I can keep working with, or should I shut down?
It's logged at Warning alarm level, but because throttle is forced to 0% while active, the machine may not respond normally to throttle input. It's best treated as a stop-and-diagnose condition rather than something to run through, since throttle control is directly affected.
Why would ECU Trim configuration cause this fault on an OEM install?
On OEM applications, the primary analog throttle is configured in the ECU on the Trim page. If that configuration doesn't match the actual throttle's voltage range, the ECU can misinterpret a normal signal as out of range low, triggering this code even with good wiring and a good sensor.
Does cycling the key clear this fault?
It depends on the configured recovery response. Under Locked Recovery, a power cycle of the ECU is required in addition to the signal becoming valid again. Under Idle Recovery or Resume Recovery, a power cycle alone isn't listed as the fix; the throttle signal itself has to become valid first.
What's the difference between SPN 91 FMI 4 and SPN 91 FMI 3?
Both are part of the same troubleshooting sequence for the primary analog throttle circuit. FMI 4 specifically points to the signal reading lower than physically possible (out of range low), while FMI 3 covers a related but distinct voltage condition on the same circuit. They share the same troubleshooting sequence with SPN 3512 FMI 3 and FMI 4.