Technical Description of OBD-II Trouble Code
Range/Performance Issue with Input/Turbine Speed Sensor “B” Circuit
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to all vehicles manufactured from 1996 onwards (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.
When the diagnostic trouble code P2766 is displayed, it indicates that the powertrain control module (PCM) has detected a malfunction in the circuit for the designated input (or turbine) speed sensor known as “B”. Although input and turbine speed sensors have similar designs, some manufacturers may use different component terminology. The designation “A” is typically reserved for OBD-II equipped vehicles that have multiple input or turbine speed sensors.
The input/turbine speed sensor is typically an electromagnetic, 3-wire sensor used to monitor the transmission’s input speed, which is recognized by the PCM as revolutions per minute (RPMs). The sensor is usually located near the rear of the torque converter, either mounted with a bolt/stud or threaded directly into the transmission case.
On the transmission’s main (or input) shaft, there are specially designed grooves (or a notched reluctor wheel). The input shaft (or reluctor wheel) passes close to the end of the sensor, completing the electromagnetic circuit. As the grooves (or notches) pass by the sensor, the circuit is interrupted and an electronic pattern is formed. The PCM receives this pattern formation as a waveform pattern, which it interprets as the transmission’s input/turbine speed.
The transmission’s input/turbine speed is compared with the engine’s RPM speed, percentage of engine load, and transmission output speed to determine the desired input speed RPM. If the actual input/turbine speed does not match the desired input/turbine speed, a code will be stored and a malfunction lamp may illuminate.
Symptoms & Severity
In some cases, when this code is stored, the PCM will put the transmission in “limp-in” mode. In this mode, the transmission will shift harshly. If you experience irregular shifting when the P2766 code is present, it is important to address the problem immediately.
Symptoms of a P2766 code may include:
Causes
Possible causes for this code to be set are:
Diagnostic and Repair Procedures
A good starting point is to always 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.
An advanced diagnostic scanner, a digital volt/ohmmeter (DVOM), a manufacturer’s service manual, and possibly an oscilloscope will be useful in diagnosing the P2766 code.
It is recommended to begin the diagnosis with a visual inspection of the system’s wiring and connectors. Any disconnected, corroded, burnt, or shorted wiring and/or connectors must be repaired or replaced. It is also important to test the battery and inspect the battery cables and cable ends. Additionally, test the alternator output.
Connecting the scanner to the diagnostic port and retrieving all stored codes, as well as noting the freeze frame data, is a good practice for future reference.
If input sensor and output sensor codes are present, use the scanner data stream to determine which circuit is at fault. For more accurate data, narrow down the data stream to include only relevant information.
Check for excessive metal debris on the magnetic surfaces of the input and/or output speed sensors. It is recommended to remove excessive debris before reinstalling. When removing the sensors, also inspect the interruption grooves and/or reluctor wheel notches.
Use the DVOM to test individual sensors according to the manufacturer’s specifications (found in the service manual or through All Data). Sensors that do not comply with the manufacturer’s specifications must be replaced. Some manufacturers recommend replacing both the input and output speed sensors as a set. Before testing resistance and continuity with the DVOM, disconnect 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.
Additional diagnostic notes:
