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:
Causes
Potential causes for this code to set are:
Diagnostic 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 output sensor codes present. To get the most accurate data available with the scanner, narrow the data stream to include only pertinent information.
Metal debris on magnetic contacts of input and/or output speed sensors can cause intermittent/erratic sensor output data. Remove the sensor and check for metallic debris. Clean excessive debris from magnetic surfaces before reinstallation. I would also inspect interruption grooves and/or reluctor wheel notches for signs of damage or wear.
I use the DVOM to test individual sensor resistance and circuit voltage by following manufacturer’s guidelines (found in the service manual or through All Data). I would replace sensors that do not comply with manufacturer’s specifications.
Controller failure may result if all related controllers are not disconnected prior to testing resistance or continuity with the DVOM.
Suspect a faulty PCM or a PCM programming error, if a code P0718 is stored and all system circuits and sensors are in proper working order and comply with manufacturer’s specifications.
Additional diagnostic notes:
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"Delete Error Code Permanently, Disable DTC Error Code Function for p0718 in the ECU"
In extreme cases, we even have the option to permanently remove the specific DTC p0718 and disable the function of the specific error code in the ECU. All other fault code functions will then continue to work to protect the engine. This is different from clearing an error code with a diagnostic device. We have the option to permanently remove the function of the specific error code, so that it never comes back. Also emergency running that occurs on the specific error code can be solved in most cases.
Of course we prefer to first try to solve the cause of the error code, but sometimes the only solution is to permanently disable the DTC function of p0718.
