P0718
Input/Turbine Speed Sensor A Circuit Intermittent
The appearance of the standard OBD2 trouble fault code P0718 is an indicator that your vehicle ECU triggered a threshold alert for "Input/Turbine Speed Sensor A Circuit Intermittent". Understanding the root component breakdown helps avoid expensive diagnostic fees.
Driver's Summary
A P0718 fault code points directly to a problem with input/turbine speed sensor a circuit intermittent that the ECM has confirmed over multiple drive cycles. On the road, this usually shows up as transmission drops out of gear randomly, erratic shifting. While the car is usually drivable, you should schedule a diagnosis within the next few days to prevent the issue from worsening.
Symptoms
Transmission drops out of gear randomly, erratic shifting
Common Causes
- Loose connector at the input speed sensor
- Wiring harness shorting intermittently
- Internally failing sensor due to heat
- TCM software issue
How to Fix
- 1 Clean and tighten sensor connection
- 2 Perform wiggle test and repair wiring
- 3 Replace the input speed sensor
- 4 Update TCM software
Technical Explanation
The PCM triggers P0718 after its internal monitoring routine detects that a specific circuit or sensor has exceeded its acceptable operating range. The TCM compares the ratio between input turbine speed sensor and output speed sensor readings against the expected gear ratio stored for each commanded gear position. A deviation greater than a few percent indicates clutch slippage, solenoid malfunction, or internal mechanical failure. After two failed drive cycles, the code transitions from a pending to a confirmed DTC, and the PCM activates the MIL. Clearing the code without repairing the fault will result in re-illumination within one to two complete drive cycles.
Is It Safe to Drive?
While the vehicle is typically drivable with P0718 active, avoid towing, aggressive acceleration, or extended highway driving until the fault is resolved. The primary risk is accelerated wear on loose connector at the input speed sensor and wiring harness shorting intermittently.
Mechanic's Pro Tip
Module replacement should always be the last resort for P0718 after exhaustively verifying all power supply circuits, ground connections, and communication bus wiring. Use a wiring diagram to locate all fuses, relays, and ground points for the affected module, and measure voltage drop on each ground with the circuit loaded. A module "failure" is frequently a corroded ground eyelet or a weak battery causing brownout conditions — fix these first and you'll save hundreds of dollars on an unnecessary module replacement.
Wiring repair: $100; Sensor replacement: $150 - $300