P0718 Input/Turbine Speed Sensor A Circuit Intermittent
OBD-II Trouble Code Technical Description
Input/Turbine Speed Sensor A Circuit Intermittent
This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles (Ford, Honda, Mazda, Mercedes, VW, etc.). Although generic, the specific repair steps may vary depending on make/model.
What does that mean?
If you are presented with a trouble code P0718, it is likely because the powertrain control module (PCM) has detected an erratic voltage input signal from the circuit of the input (or turbine) speed sensor that has been given the designation A. Although input and turbine speed sensors are virtually the same, and serve the same purpose, component terminology varies between manufacturers.
In most cases, the input/turbine speed sensor is a 3-wire, electromagnetic sensor used to monitor transmission input speed in revolutions per minute (RPM). The sensor is usually positioned near the rear of the bell housing (at the transmission input shaft) and mounted with a bolt/stud or threaded directly into the transmission case.
Either a notched reluctor wheel or specially designed grooves are permanently attached to the transmission main (or input) shaft. As the running engine 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) effectively completes an electronic/electromagnetic circuit with the sensor. An electronic pattern is formed when the circuit is interrupted by the grooved (or notched) areas passing by the sensor. The pattern is recognized by the PCM as a waveform that it is programmed to interpret as transmission input/turbine speed.
Transmission output speed, transmission input/turbine speed, engine speed, throttle position, percentage of engine load, and other factors are compared and calculated to determine the desired input/turbine RPM speed. A code P0718 will be stored (and a malfunction lamp may be illuminated) if the input/turbine speed, or system circuit voltage, fail to remain accurate within a predetermined degree for a specific amount of time.
The P0718 indicates an intermittent input circuit voltage for the input/turbine speed sensor.
Symptoms
Symptoms of a P0718 code may include:
Erratic speedometer (odometer) operation The transmission fails to shift properly Speedometer and/or odometer will not operate at all Transmission shift points are erratic or harsh Diminished fuel efficiencyCauses
Potential causes for this code to set are:
Defective input speed sensor Damaged, loose, or burnt wiring and/or connectors PCM failure or a PCM programming error Accumulation of metal debris on the magnetic sensorDiagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known issue with a known fix put out by the manufacturer and can save you time and money during diagnosis.
A digital volt/ohmmeter (DVOM), a manufacturer’s service manual, an advanced diagnostic scanner, and possibly an oscilloscope will be instrumental in diagnosing the P0718 code correctly.
I usually begin my diagnosis with a visual inspection of system wiring and connectors. I would repair any obviously shorted or open circuits and/or connectors before proceeding any further. Don’t forget to inspect the battery, battery cables, and cable ends and test alternator output at this time.
Next, I would connect the scanner to the diagnostic port and retrieve all stored codes and write them down for future reference. I’d also make a note of the freeze frame data at this time.
Use the scanner data stream to determine which circuit is malfunctioning, if there are input sensor and outp
Read: 31
