What it means
Input or Turbine Shaft Speed Sensor A Circuit Intermittent: the signal is intermittent or erratic. Often a loose connector or chafed wiring; a wiggle test often locates it.
At a glance
- Usually lights the check-engine light
How it works
Input/turbine speed sensor A reports the transmission input shaft's speed to the TCM. P0718 sets when that signal cuts in and out or becomes erratic intermittently, often because vibration moves a loose connector or a chafed harness briefly breaks contact.
Common causes
Most likely first.
- Intermittent contact at connector
- Connector with intermittent contact under vibration
- Harness routed against vibrating component
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Record freeze-frame data and review sensor A's live speed for sudden dropouts or spikes when the fault is active.
- Inspect sensor A's connector for loose retention, corrosion, moisture, and pins that may shift when touched.
- Trace the harness near vibrating or moving components and check for chafing, tension, or missing support.
- Use live data or the manufacturer's circuit test while gently moving the connector and harness to reproduce the signal interruption.
- If the harness remains stable, test sensor A for intermittent output failure according to the manufacturer's procedure.
Common fixes
- Reseat and secure sensor A's connector and clean terminals with poor contact.
- Repair chafed or intermittently open wiring and secure the harness away from vibration.
- Replace damaged connector pins or seals.
- Replace input/turbine speed sensor A if it drops out with a verified sound circuit.
Can I keep driving?
Keep trips short and avoid towing or hard acceleration while the signal is intermittent. Stop if the transmission begins slipping, shifting harshly, or entering limp mode, since loss of input speed data can disrupt shift control.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.