P2740 indicates that the powertrain control module (PCM) has detected an abnormal signal from the transmission fluid temperature sensor B circuit, which monitors the temperature of the transmission fluid to help control shift timing and torque converter lock‑up.
The sensor itself may be open, shorted, or out of calibration, causing the PCM to see an invalid voltage or resistance.
Damaged harness, chafed wires, corroded pins, or loose connector can produce intermittent or constant signal faults.
Insufficient fluid level or degraded fluid can cause the sensor to read temperatures outside its expected range, triggering the code.
A malfunctioning torque converter, clogged cooler, or internal wear can cause actual fluid temperature to be abnormal, leading to sensor B readings that are out of range.
Although sometimes suggested, the PCM rarely causes P2740; only consider after sensor, wiring, and fluid checks are normal.
No. The PCM is rarely the cause; most P2740 cases are due to a faulty temperature sensor, wiring issue, or fluid condition. Only consider PCM after those items have been verified.
Many transmissions have two fluid temperature sensors (sensor A and sensor B) for redundancy or different locations; sensor B typically monitors the temperature of the fluid exiting the torque converter or cooler circuit.
If the PCM cannot accurately monitor fluid temperature, it may allow the transmission to overheat or shift improperly, which can lead to accelerated wear; it's advisable to diagnose and repair promptly.
Clearing the code without fixing the underlying issue will likely cause the code to return and may hide a developing problem; it's better to address the root cause first.