What is SPN 51 FMI 3 & How to Solve It?

What is SPN 51 FMI 3:

SPN 51 refers to the Engine Throttle Valve Control, and FMI 3 indicates voltage above normal in the circuit.

This fault suggests a wiring short or stuck throttle valve, potentially causing poor idling, derates, or limp mode behavior.

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Why This Happens

• Throttle valve stuck or actuator shorted.
• Connector or wiring corrosion causing high voltage.
• ECM overvolting control circuit.
• Intermittent signal spikes from the sensor or actuator.

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How to Fix It

1. Test the throttle actuator for free movement and signal response.
2. Inspect wiring and connector pins for shorts or burn marks.
3. Replace the throttle valve if internally shorted.
4. Check ECM output voltage to actuator.
5. Clear the code and retest idle and throttle control.

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How to Avoid It Before It Happens

1. Include throttle control tests during scheduled services.
2. Protect connectors from water and vibration.
3. Replace valves with sluggish or inconsistent movement.
4. Log all idle/throttle complaints for review.

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