SPN 51 FMI 3 — Throttle Position Circuit Voltage Above Normal
TPS high-voltage codes are open-circuit electrical diagnostics first. Open circuits after intake service are the most documented pattern. The FSM enforces circuit-first process before assembly replacement.
Fault Overview
SPN 51 FMI 3 is a throttle position sensor circuit high voltage or open class fault where intake throttle position is monitored. Open signal, failed position sensor, connector issues, and reference voltage anomalies are the primary causes. Open circuits after intake service are a documented pattern. Replacing the throttle body assembly before proving the circuit is the most documented misdiagnosis pattern.
Engine & Platform Coverage
Symptoms
- •Throttle position high voltage
- •TPS open circuit intake throttle
- •Throttle sensor code
- •Regen enable issues from throttle fault
- •High signal with open circuit
Possible Causes
- 1.Open signal — open signal circuit producing high voltage reading
- 2.Failed position sensor — failed position sensor producing high voltage reading
- 3.Connector issues — connector issues producing open circuit
- 4.Reference voltage anomalies — reference voltage anomalies producing high signal reading
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
3 steps locked behind Technician Mode- 1Step 1 — Reference Voltage and Ground Checks: Confirm 5V reference and ground at the throttle connector cavities. Open circuits after intake service are a documented pattern — always inspect the throttle body connector after any recent intake service. Verify reference voltage and ground integrity.
- 2Step 2 — Signal Circuit Verification: Verify the signal circuit. High signal with an open circuit is common. Measure signal voltage at the throttle connector. An open signal circuit producing a high voltage reading confirms a harness or connector fault.
- 3Step 3 — Command Movement Correlation: Correlate signal with commanded movement. A signal that does not change with commanded movement confirms a sensor or circuit fault. A signal that changes correctly with commanded movement confirms the sensor is functional.
- 4Step 4 — Replace Sensor or Assembly After Circuit Proof: Replace the sensor or assembly after circuit proof. Confirm the harness and connector are clean before any replacement. A sensor or assembly replaced without circuit proof may replace a good component into a circuit fault.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
- 1Repair connector or harness if open circuit is confirmed.
- 2Replace throttle body or sensor assembly if failure is confirmed after circuit proof.
Unlock full diagnostic steps, DVOM tests, and repair procedures.
Full Diagnostic Access
Verification steps, preventative measures, severity guidance, and legacy comparison are available in Technician Mode.
Start Diagnosing This Fault Now
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Summary
TPS high-voltage codes are open-circuit electrical diagnostics first. The AI Diesel Tech FSM enforces circuit-first process before assembly replacement.