Input/Turbine Speed Sensor Circuit Intermittent
Diagnostic trouble code P0718 indicates that the Powertrain Control Module (PCM) or Transmission Control Module (TCM) has detected an intermittent, erratic, or missing signal from the input/turbine speed sensor circuit. The module sets this code when the input speed signal drops out or fluctuates unexpectedly compared to engine speed and output speed, preventing accurate transmission shift control.
While the vehicle can usually still be driven, an intermittent input speed sensor signal can cause harsh shifting, limp mode, and potential long-term transmission damage if left unaddressed. It should be diagnosed and repaired soon to ensure safe and reliable operation.
Common symptoms
- Illuminated Check Engine Light
- Harsh or erratic transmission shifting
- Transmission slipping or failure to shift
- Vehicle entering 'limp mode' (stuck in a single gear)
- Decreased fuel economy and poor acceleration
Likely causes
- Faulty input/turbine speed sensor
- Loose, corroded, or damaged wiring and connectors in the sensor circuit
- Contaminated transmission fluid containing metal debris affecting the magnetic sensor
- Faulty transmission valve body or internal mechanical failure
- Defective Powertrain Control Module (PCM) or Transmission Control Module (TCM) (rare)
What to check before replacing parts
Check the transmission fluid level and condition.
Look for: Fluid that is excessively dirty, burnt, or contains metal shavings, which can interfere with the magnetic input speed sensor.
Visually inspect the input/turbine speed sensor wiring harness and connectors.
Look for: Chafed wires, melted insulation, loose connections, or corrosion at the sensor connector that could cause an intermittent signal.
Remove and inspect the input/turbine speed sensor.
Look for: Excessive metal debris attached to the magnetic tip of the sensor, or physical damage to the sensor housing.
Test the input/turbine speed sensor resistance and AC voltage output using a digital multimeter.
Look for: Resistance values outside the manufacturer's specified range, or an erratic/missing AC voltage signal when the sensor is subjected to a rotating ferrous object.
Monitor the input/turbine speed sensor data PID using a scan tool while driving.
Look for: An RPM reading that drops to zero, spikes erratically, or does not smoothly follow engine RPM during operation, confirming the intermittent fault.
This page explains the generic P0718 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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