John Deere Engines SPN191FMI2 Fault Code: Pump Speed Input Noise
Pump Speed Input Noise · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 191 FMI 2 means the ECU sees an erratic (noisy) signal from the injection pump speed sensor while the engine speed sensor input is still valid. The engine may hesitate briefly but should keep running. If SPN 190 FMI 2 sets at the same time, the engine will die and not restart until one of the two codes is fixed.
Medium severity. On its own, this code usually causes only a momentary hesitation and the engine keeps running. It becomes far more serious if it occurs together with SPN 190 FMI 2, which can stall the engine and prevent a restart until repaired.
What does John Deere Engines error code SPN191FMI2 mean?
SPN 191 FMI 2 points to the pump speed sensor, an inductive pickup located inside the injection pump that reads notches on the pump's internal timing wheel to generate an AC signal proportional to pump speed. This signal serves as a backup to the primary engine speed sensor. If the main engine speed signal ever has a problem, the ECU switches over to the pump speed sensor input so the engine can keep running.
This fault sets when the pump speed sensor input becomes erratic or 'noisy' while the engine speed sensor input is still reading correctly. In other words, the backup signal is misbehaving even though the primary signal is fine, so the ECU flags it.
By itself, the engine may hesitate momentarily but should continue running normally. The real risk is if SPN 190 FMI 2 (engine speed sensor fault) also sets. When both codes are present together, the engine will die and will not restart until at least one of the two underlying problems is repaired.
Common causes of SPN191FMI2
- Dirt, damage, or poorly seated terminals on the ECU 30-way connector and the 6-way pump or engine speed sensor connector
- Bad harness connectors
- Faulty alternator connections
- Bad chassis ground or battery ground connections
- Corrosion, dirt, or paint causing intermittent, noisy connections
- Intermittent open or short circuits in the wiring harness, particularly the pump speed sensor wiring
- Electromagnetic interference (EMI) from an incorrectly installed two-way radio
- Interference from a radar source
- Excessive electrical noise in the system
How to troubleshoot John Deere Engines SPN191FMI2: first checks
- Inspect the ECU 30-way connector and the 6-way pump and engine speed sensor connectors for dirt, damage, corrosion, or terminals that are pushed back or poorly seated
- Check all harness connectors along the pump speed sensor wiring for corrosion, dirt, or paint buildup that could cause an intermittent connection
- Verify chassis ground and battery ground connections are clean, tight, and free of corrosion
- Check alternator connections for looseness or corrosion
- Inspect the wiring harness for intermittent open or short circuits, focusing on the pump speed sensor circuit
- Look for any recently installed two-way radio or radar equipment that may be creating electromagnetic interference near the engine wiring
- Use the JT07328 Connector Adapter Test Kit to make any electrical measurements in the connectors, never force probes directly into connector terminals since this can damage the terminals
How the code clears
No separate clearing step is listed for this code. Repairing the underlying wiring, connector, grounding, or interference issue should allow the fault to clear on its own once the pump speed sensor input is no longer erratic. If SPN 190 FMI 2 is also present, at least one of the two codes must be repaired before the engine will restart.
Frequently asked questions
What does SPN 191 FMI 2 mean on a John Deere engine?
It means the ECU detected an erratic or noisy signal from the injection pump speed sensor while the engine speed sensor input was still valid. The pump speed sensor is a backup to the main engine speed sensor, and this fault flags a problem specifically with that backup signal path.
Will SPN 191 FMI 2 stop my engine from running?
Usually not by itself. The engine may hesitate momentarily but should continue running normally. It becomes a bigger problem if SPN 190 FMI 2 also sets, because together they will cause the engine to die and it won't restart until at least one of the two codes is repaired.
What usually causes this fault?
Common causes include dirty, damaged, or poorly positioned terminals on the ECU or pump connectors, bad harness connectors, faulty alternator connections, bad ground connections, corrosion or paint on connections, intermittent open or short circuits in the wiring (especially the pump speed sensor circuit), and electrical interference from equipment like a two-way radio or radar source.
Can a two-way radio really cause this code?
Yes. An incorrectly installed two-way radio can generate electromagnetic interference that disrupts the pump speed sensor's signal, causing the ECU to see it as erratic even though the sensor itself is fine.
How do I check the connectors without damaging them?
Use the JT07328 Connector Adapter Test Kit to take measurements. Do not force probes directly into the connector terminals, since that can damage them and create new problems.
Is there a specific reset procedure for this code?
No separate clearing step is listed for this code. Once the underlying wiring, connector, ground, or interference issue is fixed, the fault should stop recurring on its own.
Why does the ECU care about the pump speed sensor if the engine speed sensor is working fine?
The pump speed sensor acts as a backup. If the engine speed sensor input ever fails, the ECU switches to the pump speed sensor so the engine can keep running. A noisy pump speed signal means that backup path isn't reliable, which is worth fixing even if the primary sensor is currently fine.