Transmission

P0718 — Input/Turbine Speed Sensor Circuit Intermittent

Severity: medium Drive with care, to a shop

What P0718 means

The transmission control module (TCM) monitors the speed of the input shaft or torque converter turbine through a speed sensor. P0718 sets when that signal drops out or becomes erratic from time to time instead of failing completely. Without a reliable input speed, the module cannot judge clutch slip or time shifts correctly.

Symptoms

  • Random limp mode
  • Flared or delayed shifts, engine revving between gears
  • Harsh or bumpy shifts
  • Check Engine light on
  • Possible reduced power
  • Erratic speedometer or tachometer on some vehicles

Possible causes

  1. Intermittently failing input speed sensor (TSS)
  2. Corroded or loose connector at the transmission or pan
  3. Internal wire breaks in the harness from fatigue
  4. Damaged wiring: open, chafed or shorted to ground
  5. Poor connection at the control module connector
  6. Faulty TCM or PCM
  7. Metal debris on the sensor's magnetic tip

How to diagnose

  1. Scan all codes and read freeze frame data to see when the fault sets
  2. Watch input speed in live data and compare it with engine rpm and output shaft speed
  3. Wiggle the harness and connector with the engine running and watch for signal dropouts
  4. Inspect the transmission connector for corrosion, moisture and loose or spread terminals
  5. Check fluid level and condition, and look for metal debris
  6. Remove the sensor and inspect its tip and seal
  7. Test the sensor wiring for opens and shorts, and check sensor resistance against specification
  8. Verify power and ground at the TCM

Common fixes

  • Replace the input speed sensor
  • Clean and repair the connector or replace damaged terminals
  • Repair or replace the damaged section of harness
  • Change transmission fluid and filter if contaminated
  • Reprogram or replace the TCM once it is confirmed faulty

Questions and answers

What does P0718 mean?

The transmission control module is getting an intermittent signal from the input/turbine speed sensor. A bad connection in the connector or wiring, or the sensor itself, is the most common cause.

Can I drive with P0718?

Only briefly and carefully, such as to a shop. The transmission may suddenly enter limp mode, and prolonged driving with harsh or slipping shifts speeds up wear.

How much does it cost to fix P0718?

It depends on the cause: cleaning a connector is cheapest, a new sensor costs more, and harness or module repair costs more still. Only a proper diagnosis can tell which applies.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.