What Does P0940 Mean?
DTC P0940 indicates the hydraulic oil temperature sensor is reporting a voltage signal above the maximum expected threshold. With NTC thermistor sensors, a high voltage signal corresponds to low resistance, suggesting the sensor circuit may be shorted to ground or the sensor element has failed low-resistance. The TCM interprets this as an unrealistically high temperature reading.
Common Causes
30%
Hydraulic oil temperature sensor shorted internally (low resistance failure)
25%
Signal wire shorted to ground in the wiring harness
20%
Moisture intrusion in the sensor connector causing a short circuit
15%
Damaged or melted wiring near exhaust or other heat sources
10%
Actual severe hydraulic fluid overheating due to cooling system failure
Diagnostic Steps
1
Step 1: Check the scan tool reading for hydraulic oil temperature. An extremely high reading (250F+ when the vehicle has not been driven hard) suggests a sensor or circuit fault rather than actual overheating.
2
Step 2: Disconnect the sensor and measure its resistance. A reading significantly below specifications (near 0 ohms) indicates an internally shorted sensor.
3
Step 3: With the sensor disconnected, check if the signal wire is shorted to ground by measuring resistance between the signal wire and chassis ground at the TCM connector.
4
Step 4: Inspect the wiring harness routing for damage, especially near heat sources like exhaust components. Look for melted insulation or pinched wires.
5
Step 5: If the sensor and wiring check out, verify actual fluid temperature with an infrared thermometer. If the fluid is genuinely overheating, investigate the transmission cooler and cooling circuit.
Estimated Repair Cost
$100 - $400
Parts + labor, varies by vehicle and location
DTC P0940 indicates the hydraulic oil temperature sensor is reporting a voltage signal above the maximum expected threshold. With NTC thermistor sensors, a high voltage signal corresponds to low resistance, suggesting the sensor circuit may be shorted to ground or the sensor element has failed low-r...
The most common cause of P0940 (Hydraulic Oil Temperature Sensor Circuit High Input) is: Hydraulic oil temperature sensor shorted internally (low resistance failure)
Typical repair costs for P0940 range from $100 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A falsely high temperature reading may cause the TCM to enter a protective mode, reducing line pressure or limiting shift patterns. If the overheating is genuine, continued driving risks severe transmission damage including burnt clutch packs and warped components.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0940 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission / Clutch Hydraulic System
Difficulty
Type
Generic (SAE)
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