P2742 indicates the powertrain control module (PCM) has detected a signal voltage from Transmission Fluid Temperature (TFT) Sensor 'B' that is lower than the calibrated range. Because most TFT sensors are negative-temperature-coefficient thermistors, a 'low' circuit reading usually reports an abnormally high fluid temperature or a short/open in the sensor circuit.
The thermistor element inside the sensor can drift out of range, internally short, or open, sending a constant low-voltage signal to the PCM. This is the single most common root cause for this code.
The signal or reference-voltage wire may be rubbed through, pinched, or corroded, creating a path to ground or an open that pulls the circuit voltage below the expected threshold.
Water intrusion, terminal spread, or corrosion at the sensor or harness connector can increase resistance or create an intermittent short, producing a low circuit reading.
On units where the sensor is mounted on an internal conductor plate or routed through the transmission case pass-through, internal harness damage can mimic a failed sensor.
A rare internal PCM reference-voltage or analog-input failure can set this code; it should only be considered after the sensor, harness, and connectors have been verified good.
It is not advisable to continue driving. The PCM may command protective limp mode or disable normal shift scheduling to guard against perceived overheating, which can be unsafe and accelerate transmission wear.
Usually no. Most instances are caused by a failed sensor, wiring short, or connector problem. PCM replacement is one of the least likely fixes and should only be considered after the sensor and entire circuit are proven good.
Location varies by transmission design, but Sensor B is typically mounted in the valve body area, transmission pan, or on an internal conductor plate. Service information for the specific application should be consulted before removal.
Most TFT sensors are thermistors whose resistance drops as fluid temperature rises. If the signal voltage is pulled low, the PCM interprets it as either very hot fluid or a short/open in the sensor circuit.