John Deere Engines SPN3512FMI4 Fault Code: Sensor Supply #4 Voltage Out of Range Low
Also called Engine Shutdown Commanded by Application
Sensor Supply #4 Voltage Out of Range Low · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN3512 FMI4 sets when the ECU sees the Sensor Supply #4 circuit drop below 4.6 V. This 5-volt supply feeds the primary analog throttle and, on some applications, the fan speed sensor, PTO speed sensor, A/C high pressure switch, and isochronous/droop governor switch. The code carries a Warning alarm level and is displayed when the ignition is on and the fault is active.
Medium severity. Alarm level is listed as Warning, not a shutdown code by itself. Still, a low sensor supply can affect throttle input and other connected sensors, so it should be diagnosed the same shift rather than ignored.
What does John Deere Engines error code SPN3512FMI4 mean?
SPN3512 FMI4 means the engine ECU has detected that its Sensor Supply #4 circuit, a regulated 5-volt reference supply, has dropped below 4.6 V. This supply line feeds several sensors and switches so they can send an accurate signal back to the ECU. When the supply voltage sags, any device on that circuit can send bad or unstable readings even though the device itself may be fine.
The ECU responds by trying to maintain proper operating conditions on the circuit, but it cannot force voltage above the current-limit protection built into the supply. If too many devices, or a shorted device, pull excess current from Sensor Supply #4, the ECU will activate a current-limit shutdown on that supply rather than let it be damaged.
Depending on the application, the devices sharing this 5-volt supply can include the primary analog throttle, an optional fan speed sensor, an optional PTO speed sensor, an optional A/C high pressure switch, and an optional isochronous/droop governor switch. Because the primary analog throttle is almost always tied to this circuit, this fault is worth taking seriously even at Warning level.
What triggers a John Deere Engines SPN3512FMI4 code?
The ECU sets this code when it detects supply voltage less than 4.6 V on the Sensor Supply #4 circuit, with the ignition on and the fault condition active.
Common causes of SPN3512FMI4
- A bad or shorted primary analog throttle, fan speed sensor, PTO speed sensor, A/C high pressure switch, or isochronous/droop governor switch pulling the supply down
- A short in the wiring harness feeding Sensor Supply #4
- Corroded, loose, or damaged terminals or connector pins at the ECU
- Corroded, loose, or damaged terminals or connector pins at the primary analog throttle or other connected sensor/switch
- Bad or corrupted ECU software
- A faulty ECU itself
- On some applications, bad terminals or connector at the control panel connector (X5021) or a bad instrument panel
How to troubleshoot John Deere Engines SPN3512FMI4: first checks
- Check how many devices are wired to Sensor Supply #4. Too many devices, or one drawing excess current, will trip the ECU's current-limit shutdown on this supply
- Inspect the primary analog throttle and any connected fan speed sensor, PTO speed sensor, A/C high pressure switch, or isochronous/droop governor switch for damage or an internal short
- Inspect the wiring harness between the ECU and these components for chafed, pinched, or shorted wiring
- Check ECU connector terminals and pins for corrosion, looseness, or damage
- Check terminals and connectors at each device using Sensor Supply #4, and at the control panel connector if equipped
- Confirm ECU software is current and not corrupted before condemning the ECU itself
How the code clears
No separate clearing step is listed for this code. Once the underlying cause (shorted component, damaged wiring, bad connector, or ECU fault) is repaired and the supply voltage returns above the 4.6 V threshold, the active fault should clear on its own with the ignition cycled on.
Frequently asked questions
What does SPN3512 FMI4 mean on a John Deere engine?
It means the ECU detected the Sensor Supply #4 circuit voltage below 4.6 V. This is a regulated 5-volt supply that feeds the primary analog throttle and, on some machines, other optional sensors and switches.
Is SPN3512 FMI4 a serious fault?
It is listed at Warning alarm level, not an automatic shutdown. But since it can affect throttle input and other connected sensors, it should be diagnosed promptly rather than run indefinitely.
What components use Sensor Supply #4?
The primary analog throttle always, plus optionally the fan speed sensor, PTO speed sensor, A/C high pressure switch, and isochronous/droop governor switch. Some applications have additional device combinations, so check the application technical manual for your machine.
Can too many accessories cause this code?
Yes. If too many devices are connected to Sensor Supply #4, or if the load is too great, the ECU will activate a current-limit shutdown on that supply, which can trigger this code.
What should I check first for SPN3512 FMI4?
Start with the number and condition of devices on Sensor Supply #4, then inspect the primary analog throttle and related sensors/switches, the harness wiring, and all connector terminals at the ECU and each device before considering ECU software or hardware.
Does this code always mean the ECU is bad?
No. A bad ECU or bad ECU software is on the list of possible causes, but shorted components, damaged harness wiring, and corroded connectors are more common and should be ruled out first.
How is this code related to SPN91 FMI3 or SPN3512 FMI3?
These codes are listed together in the troubleshooting sequence for Sensor Supply #4 issues. Technicians typically work through SPN91 FMI3 and SPN3512 FMI3 as part of the same diagnostic path before or alongside SPN3512 FMI4.