P0718
Input/Turbine Speed Sensor Circuit No Signal
Powertrain Transmission Control Input speed sensor 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

Your transmission's speed sensor isn't sending a signal to the engine computer, like a speedometer that's stopped working. Without this information, the transmission can't shift gears properly or adapt to driving conditions.

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Symptoms You May Notice
3 known symptoms for this code
Transmission stuck in limp mode or default gear
Poor fuel economy and sluggish acceleration
Check engine light illuminated
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECM monitors voltage signals from the turbine/input speed sensor to track transmission fluid flow and gear engagement. It expects a frequency signal proportional to input shaft speed; absence of this signal for a calibrated duration triggers the fault. The sensor typically generates AC voltage or digital pulses as the shaft rotates.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Turbine Speed Signal Frequency 10-10,000 Hz depending on engine load and gear No signal or signal below minimum threshold for >2 seconds
Sensor Voltage Output 0.2–4.8V (varies by sensor type) Constant 0V or 5V with no variation
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Turbine speed sensor connector
Inspect and reseat the connector at the transmission; corrosion or loose pins often cause no-signal faults.
2
Wiring harness to turbine sensor
Check for damaged or pinched wires between sensor and ECM using a multimeter to test continuity.
3
Turbine speed sensor
Replace the sensor if wiring and connectors test good; sensor failure is common on high-mileage transmissions.