Transmission Fluid Temperature Sensor "A" Circuit Range/Performance

Possible causes

• CommonFailed or drifting temperature sensor
• CommonLow fluid level, so the sensor is not properly immersed
• CommonHigh resistance in the wiring or a corroded connector, skewing the reading
• PossibleFluid cooler blocked or bypassed, so the fluid genuinely is the wrong temperature
• PossibleWrong sensor fitted at a previous repair

What you might notice

• Harsh or delayed shifting
• Torque converter locking too early or not at all
• Transmission overheat warning with no overheating
• Check engine light on

What to check, in order

1. Watch the fluid temperature climb from cold on the live data screen. It should rise smoothly and settle. A reading that jumps, sticks or never moves identifies the fault.
2. Check the fluid level first - a low level uncovers the sensor and produces exactly this code with a perfectly good sensor.
3. Check the transmission fluid cooler and its lines. If the fluid really is running too hot, the sensor is right and the cooler is the fault.
4. Measure the sensor resistance cold against specification if it is accessible.
5. Check for high resistance in the wiring and connector before condemning an internal sensor.