John Deere Engines SPN190FMI5 Fault Code: Engine Speed Sensor Circuit Open
Engine Speed Sensor Circuit Open · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 190 FMI 5 means the John Deere ECU has detected an open circuit in the engine speed input. On engines with a backup injection pump speed sensor, the ECU switches over and the engine keeps running normally. On engines without a backup speed sensor, the engine will die and will not restart.
High severity. Consequence depends heavily on whether the engine has a backup injection pump speed sensor. If it does not, this fault causes an immediate stall with no restart, which can happen anywhere, including in traffic or mid-lift. Even on engines with a backup sensor, the loss of the primary speed signal should be diagnosed promptly since it removes a layer of redundancy.
What does John Deere Engines error code SPN190FMI5 mean?
SPN 190 FMI 5 is set when the ECU detects an open in the engine speed input circuit. The engine speed sensor is an inductive pickup mounted in the timing gear cover. It reads teeth on the camshaft drive gear as they rotate past, generating an AC signal whose frequency is proportional to engine speed. The ECU uses this signal to know how fast the engine is turning, which affects fueling, timing, and other control decisions.
On most applications there is a second speed sensor built into the injection pump that acts as a backup if the primary engine speed sensor fails. If your engine has this backup sensor, the ECU will automatically switch to it when SPN 190 FMI 5 sets, and the engine will continue running normally, though the fault should still be diagnosed since the backup redundancy is now gone.
On some applications the engine speed sensor is the only speed sensor available. On these engines, an open in the speed input circuit means the ECU has no way to determine engine speed, so the engine will die and will not restart until the fault is corrected.
Common causes of SPN190FMI5
- Dirt, damage, or poorly positioned terminals on the ECU 30-way connector or on the engine speed sensor connector
- A bad engine speed sensor
- An open in the engine speed input circuit (wiring between the sensor and ECU)
- A bad ECU
- An open in the engine speed ground circuit
How to troubleshoot John Deere Engines SPN190FMI5: first checks
- Inspect the ECU 30-way connector and the engine speed sensor connector for dirt, corrosion, damaged pins, or terminals that are pushed back or poorly seated
- Check the wiring harness between the engine speed sensor and the ECU for opens, chafing, or damaged insulation, including the ground circuit for that sensor
- Use the JT07328 Connector Adapter Test Kit to safely check voltage and continuity in the connectors; do not force probes directly into the connector terminals, since this can damage them and create new problems
- Test the engine speed sensor itself for a bad signal or internal open, and check that it is properly positioned in the timing gear cover
- If the sensor, wiring, and connectors all check out, consider the ECU itself as a possible cause
How the code clears
No separate clearing step is listed. Once the open circuit in the engine speed input or ground circuit is repaired, or the sensor, connector, or ECU issue is corrected, the fault should stop setting on its own as the ECU begins receiving a valid speed signal again. On engines with a backup injection pump speed sensor, verify that the ECU returns to using the primary engine speed sensor once repairs are complete.
Frequently asked questions
What does SPN 190 FMI 5 mean on a John Deere engine?
It means the ECU has detected an open in the engine speed input circuit. This is the wiring and sensor system that tells the ECU how fast the engine is turning.
Will my engine keep running with this fault code?
It depends on your engine. If it has a backup injection pump speed sensor, the ECU switches to that backup and the engine keeps running normally. If your engine does not have a backup speed sensor, the engine will die and will not restart.
What usually causes an open engine speed circuit?
Common causes include dirty, damaged, or poorly positioned terminals on the ECU 30-way connector or speed sensor connector, a failed engine speed sensor, an open in the speed input wiring, an open in the sensor's ground circuit, or occasionally a bad ECU.
Where is the engine speed sensor located?
It is an inductive pickup sensor mounted in the timing gear cover. It reads the teeth on the camshaft drive gear to generate a speed signal.
Can I check the connectors myself before taking it to a shop?
Yes, a visual inspection for dirt, corrosion, and damaged or misaligned terminals is a reasonable first step. Just avoid forcing test probes directly into the connector terminals, since that can damage them. A proper connector adapter test kit like the JT07328 is meant for making safe measurements without causing terminal damage.
If the engine dies and won't restart, is it safe to keep trying to crank it?
Repeated cranking without addressing the underlying open circuit is unlikely to restart the engine and can drain the battery or add wear. It is better to inspect the connectors and wiring for obvious issues before continuing to crank.
Does this code mean the ECU is bad?
Not necessarily. A bad ECU is listed as a possible cause, but it is one of several, and connector, sensor, and wiring issues are more common starting points to check first.