Open circuit in the sensor signal wire, such as a broken wire or disconnected connector; Short to voltage on the signal circuit, often from chafed wiring touching a power wire; Faulty hydraulic oil temperature sensor (thermistor) reading out of range; Corroded, loose, or water-intruded electrical connector at the sensor or TCM; Failed transmission control module (TCM) driver circuit for the sensor; Poor ground connection for the sensor or TCM, causing a reference voltage offset

DTC codes / P09xx · Transmission / P0940

P0940Hydraulic Oil Temperature Sensor Circuit High

Q: What does code P0940 mean?

Hydraulic Oil Temperature Sensor Circuit High. P0940 means the transmission control module (TCM) has detected an abnormally high voltage on the hydraulic oil temperature sensor circuit, which usually indicates an open circuit, a short to voltage, or a faulty sensor. The TCM expects a voltage within a calibrated range that corresponds to the actual fluid temperature, and a reading above that range sets this code.

P0940 means the transmission control module (TCM) has detected an abnormally high voltage on the hydraulic oil temperature sensor circuit, which usually indicates an open circuit, a short to voltage, or a faulty sensor. The TCM expects a voltage within a calibrated range that corresponds to the actual fluid temperature, and a reading above that range sets this code.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaTransmission

Symptoms you may notice

Illumination of the malfunction indicator lamp (MIL) on the dashboard
Often no symptoms besides the warning light, especially if the fault is intermittent
Harsh or delayed transmission shifts as the TCM may default to a fail-safe strategy
Transmission may stay in a single gear or refuse to downshift
Erratic or inconsistent shift quality when the transmission is cold or hot
In rare cases, the transmission may enter limp mode and limit vehicle speed

Common causes, most likely first

Open circuit in the sensor signal wire, such as a broken wire or disconnected connector
Short to voltage on the signal circuit, often from chafed wiring touching a power wire
Faulty hydraulic oil temperature sensor (thermistor) reading out of range
Corroded, loose, or water-intruded electrical connector at the sensor or TCM
Failed transmission control module (TCM) driver circuit for the sensor
Poor ground connection for the sensor or TCM, causing a reference voltage offset

How to diagnose and fix it

Scan all modules for stored and pending codes, and record freeze-frame data for P0940 to see the reported temperature and voltage
Visually inspect the sensor connector and wiring for damage, corrosion, or loose pins, and repair as needed
Disconnect the sensor and measure its resistance with a multimeter, comparing to the manufacturer's temperature-resistance chart
Check the signal circuit for an open or short to voltage using a multimeter and wiring diagram, repairing any wiring fault
Verify the sensor reference voltage and ground at the connector with the key on, engine off
If wiring and sensor test good, substitute a known-good sensor or simulate the signal with a resistor box to see if the code changes
Clear codes and perform a road test to confirm the repair, monitoring live temperature data for normal operation

What the voltage reading really tells you

A high voltage on a temperature sensor circuit almost always means the signal wire is open, because the TCM pulls the signal line up to a reference voltage and the sensor pulls it down; an open circuit leaves the voltage high.
Do not replace the sensor before checking the wiring, since a broken wire or corroded connector is far more common than a failed thermistor on this circuit.
The hydraulic oil temperature sensor is often integrated into the transmission valve body or solenoid pack, so a failed sensor may require replacing the entire assembly rather than a stand-alone part.
Intermittent P0940 codes that appear only in cold or wet weather often point to a connector issue or a wire chafe that opens when the harness contracts or moves.
A weak battery or charging system problem can cause the TCM to log false high-voltage sensor codes, so always verify system voltage is stable before condemning the sensor.

Can I keep driving with P0940?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy loads, towing, or aggressive driving because the transmission may be in a fail-safe mode with harsh shifts. If the transmission is stuck in limp mode or the warning light is accompanied by severe drivability problems, stop and have the vehicle towed.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.