What Does P0939 Mean?
DTC P0939 indicates the hydraulic oil temperature sensor is producing a voltage signal below the expected minimum threshold. Since most transmission temperature sensors are negative temperature coefficient (NTC) thermistors, a low voltage signal typically corresponds to a high resistance reading, which could indicate an open circuit, disconnected sensor, or extremely cold fluid. The TCM sets this code when the signal drops below the calibrated floor for normal operation.
Common Causes
30%
Open circuit in the sensor wiring or sensor itself
25%
Disconnected or corroded sensor connector
25%
Faulty hydraulic oil temperature sensor (high resistance failure)
15%
Damaged wiring harness with broken conductor
5%
TCM connector pin backed out or damaged
Diagnostic Steps
1
Step 1: Verify the hydraulic oil temperature sensor connector is fully seated and not disconnected. A loose connector is the most common cause of low-input codes on temperature sensors.
2
Step 2: Measure voltage at the sensor connector signal pin with the key on. If reading near 0V or below 0.3V, the circuit has a low-input fault.
3
Step 3: Check the sensor resistance with a multimeter (sensor disconnected). An NTC sensor should read approximately 2-4k ohms at room temperature. An extremely high or infinite reading indicates an open sensor.
4
Step 4: Test wiring continuity between the sensor connector and TCM connector for the signal and ground wires. Repair any open circuits.
5
Step 5: Replace the hydraulic oil temperature sensor if it fails resistance testing. Clear codes and verify the temperature reads correctly through a full warm-up cycle.
Estimated Repair Cost
$100 - $380
Parts + labor, varies by vehicle and location
DTC P0939 indicates the hydraulic oil temperature sensor is producing a voltage signal below the expected minimum threshold. Since most transmission temperature sensors are negative temperature coefficient (NTC) thermistors, a low voltage signal typically corresponds to a high resistance reading, wh...
The most common cause of P0939 (Hydraulic Oil Temperature Sensor Circuit Low Input) is: Open circuit in the sensor wiring or sensor itself
Typical repair costs for P0939 range from $100 to $380, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A low-input temperature reading may cause the TCM to assume the fluid is extremely cold, resulting in elevated line pressures and harsh shifts. This can accelerate wear on clutch packs and bands. The vehicle will typically remain drivable but should be repaired promptly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0939 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission / Clutch Hydraulic System
Difficulty
Type
Generic (SAE)
Recommended Tools
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