Symptoms
Symptoms of a P2768 code may include:
- Erratic operation of the speedometer (odometer)
- Transmission not functioning properly
- The speedometer and/or odometer will not work at all
- Transmission shift points are irregular or harsh
- Reduced fuel efficiency
Causes
Potential causes for setting this code are as follows:
- Faulty input speed sensor B
- Damaged, loose, or burnt wiring and/or connectors
- PCM failure or PCM programming error
- Accumulation of metallic debris on the magnetic sensor
Diagnostic and Repair Procedures
A good starting point is always to check the technical service bulletins (TSBs) for your specific vehicle. Your issue may be a known problem with a known fix released by the manufacturer and can save you time and money when diagnosing.
A digital volt/ohmmeter (DVOM), manufacturer’s service manual, advanced diagnostic scanner, and possibly an oscilloscope will be essential to properly diagnose the P2768 code.
I usually start my diagnosis with a visual inspection of the system’s wiring and connectors. I would repair any obviously shorted or open circuits and/or connectors before proceeding. Remember to inspect the battery, battery cables, and cable ends, and test the alternator output at this stage.
Next, I would connect the scanner to the diagnostic port and retrieve all stored codes, noting them for future reference. I would also take note of the freeze frame data at that moment.
Use the scanner’s data stream to determine which circuit is malfunctioning, if input sensor and output sensor codes are present. To get the most accurate data available with the scanner, refine the data stream to include only relevant information.
Metallic debris on the magnetic contacts of the 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 the magnetic surfaces before reinstalling. I would also inspect the interruptor grooves and/or reluctor wheel notches for signs of damage or wear.
I use the DVOM to test the individual sensor resistance and circuit voltage following the manufacturer’s guidelines (found in the service manual or via AllData). I would replace sensors that do not meet the manufacturer’s specifications.
A controller failure can occur if all associated controllers are not disconnected before testing resistance or continuity with the DVOM.
Suspect a faulty PCM or PCM programming error if a P2768 code is recorded and all system circuits and sensors are in good working order and meet the manufacturer’s specifications.
Additional Diagnostic Notes:
- Excessive metallic debris (attracted by the electromagnetic sensor) can cause erratic input/output speed sensor readings
- The gap between the sensor and the reluctor is critical. Ensure that mounting surfaces/threaded holes are free of debris and obstructions
- If the input and/or output speed sensors need to be removed from the transmission case, be cautious. Hot transmission fluid may leak from the opening
- Look for transmission fluid in the input speed sensor connector area, as some sensors tend to leak internally