Technical Description of OBD-II Trouble Code
The circuit for the Input/Turbine Speed Sensor A is experiencing intermittent issues.
This diagnostic trouble code (DTC) is a generic powertrain code that applies to OBD-II equipped vehicles from various manufacturers such as Ford, Honda, Mazda, Mercedes, VW, etc. While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
What does that mean?
If you encounter trouble code P0718, it is likely because the powertrain control module (PCM) has detected an inconsistent voltage input signal from the circuit of the input (or turbine) speed sensor designated as A. Although input and turbine speed sensors serve the same purpose and are virtually the same, different manufacturers may use different terminology for these components.
In most cases, the input/turbine speed sensor is a 3-wire, electromagnetic sensor used to monitor the transmission’s input speed in revolutions per minute (RPM). It is usually positioned near the rear of the bell housing, at the transmission input shaft, and is mounted with a bolt/stud or threaded directly into the transmission case.
The transmission’s main (or input) shaft is equipped with a notched reluctor wheel or specially designed grooves that are permanently attached. As the engine runs and transfers RPMs to the transmission, the input shaft (or reluctor wheel) passes close to the end of the sensor. The steel shaft (or reluctor wheel) completes an electronic/electromagnetic circuit with the sensor. When the grooved (or notched) areas pass by the sensor, the circuit is interrupted, creating an electronic pattern. The PCM recognizes this pattern as a waveform that it is programmed to interpret as the transmission’s input/turbine speed.
Various factors such as transmission output speed, engine speed, throttle position, percentage of engine load, and others are compared and calculated to determine the desired input/turbine RPM speed. If the input/turbine speed or system circuit voltage deviates from the predetermined degree of accuracy for a specific amount of time, a code P0718 will be stored (and a malfunction lamp may illuminate).
The P0718 code indicates an intermittent input circuit voltage issue for the input/turbine speed sensor.
Symptoms
Symptoms associated with a P0718 code may include:
Causes
Possible causes for this code to be set are:
Diagnostic and Repair Procedures
It is always a good idea to check for technical service bulletins (TSB) specific to your vehicle. There may be a known issue with a known fix provided by the manufacturer, which can save time and money during diagnosis.
To diagnose the P0718 code correctly, you will need a digital volt/ohmmeter (DVOM), a manufacturer’s service manual, an advanced diagnostic scanner, and possibly an oscilloscope.
Start by visually inspecting the system wiring and connectors. Repair any obvious shorted or open circuits and/or connectors before proceeding. Also, inspect the battery, battery cables, cable ends, and test the alternator output.
Next, connect the scanner to the diagnostic port and retrieve all stored codes. Write them down for future reference and make note of the freeze frame data.
Use the scanner data stream to identify the malfunctioning circuit if there are input sensor and output sensor codes present. Narrow down the data stream to include only relevant information for the most accurate data available.
Metal debris on the magnetic contacts of the input and/or output speed sensors can cause intermittent or erratic sensor output data. Remove the sensor and check for metallic debris. Clean excessive debris from the magnetic surfaces before reinstalling. Also, inspect the interruption grooves and/or reluctor wheel notches for signs of damage or wear.
Use the DVOM to test the resistance and circuit voltage of individual sensors following the manufacturer’s guidelines found in the service manual or through All Data. Replace sensors that do not comply with the manufacturer’s specifications.
When testing resistance or continuity with the DVOM, make sure to disconnect all related controllers to avoid controller failure.
If all system circuits and sensors are in proper working order and comply with the manufacturer’s specifications, suspect a faulty PCM or a PCM programming error if code P0718 is stored.
Additional diagnostic notes:
