Input/Turbine Speed Sensor A Circuit Intermittent
The P0718 code indicates an intermittent signal from the input/turbine speed sensor (also known as the transmission speed sensor) in the transmission. This sensor monitors the rotational speed of the torque converter turbine, which is used by the powertrain control module (PCM) to control shift timing and torque converter lockup. An intermittent circuit fault means the signal is erratic or drops out occasionally, often due to wiring issues, poor connections, or a failing sensor. This can lead to harsh shifting, incorrect shift points, or limp mode.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Harsh or erratic shifting
- Transmission stuck in limp mode (e.g., 2nd gear only)
- Delayed engagement or slipping
- Poor fuel economy
2. Most Common Causes
- Faulty or internally worn input/turbine speed sensor (NT sensor)
- Loose, oxidized, or corroded electrical connections in the sensor circuit
- Wiring damaged by chafing, heat, or chemicals causing intermittent shorts or opens
- Moisture or contamination in the transmission harness connector
- Intermittent TCM failure (less common)
- Mechanical damage to the sensor's reluctor ring or exciter gear
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data to confirm P0718 and check for related codes.
Step 2: Inspect transmission fluid level and condition; top off or replace if necessary.
Step 3: Visually check the sensor wiring and connector for damage, corrosion, or loose pins; repair as needed.
Step 4: Test the sensor resistance and AC voltage output while rotating the transmission; compare to manufacturer specs.
Step 5: If sensor and wiring are okay, check for intermittent shorts by wiggling harness while monitoring sensor signal with a scan tool or oscilloscope.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances with P0718, as it can cause erratic shifting and potential transmission damage. If the transmission enters limp mode, you may be able to drive to a repair shop at low speed, but avoid heavy acceleration or towing.
How much does it cost to fix?▼
The cost to diagnose and repair P0718 typically ranges from $50 to $150 for a sensor replacement, plus labor. If wiring repairs are needed, costs may be higher. Diagnostic fees are usually around $100-$150.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.