OBD-II Generic Error Code P0939: How to Fix It

Q: What does OBD-II code P0939 mean?

P0939 means the powertrain control module (PCM) has detected a low voltage signal from the hydraulic oil temperature sensor. This sensor monitors the temperature of hydraulic fluid in the transmission or hydraulic system, and a low reading suggests a faulty sensor, damaged wiring, or low/bad fluid.

Q: Can I drive my car with a P0939 code?

You can drive short distances with P0939, but it is not recommended for extended driving. The code indicates the PCM cannot accurately monitor hydraulic fluid temperature, which means it cannot protect the transmission from overheating. Continued driving without addressing it could lead to transmission damage, especially under heavy load or in hot conditions.

Q: Will low transmission fluid cause P0939?

Yes, low hydraulic or transmission fluid can cause inaccurate sensor readings and contribute to P0939. Low fluid levels can also allow the sensor to read improperly if it is not fully submerged. Always check and correct the fluid level as a first diagnostic step before replacing any parts.

Q: How much does it cost to fix a P0939 code?

If the fix is simply topping off or replacing hydraulic fluid, costs are minimal — usually $10 to $50 for fluid. A replacement hydraulic oil temperature sensor typically costs $20 to $150 for the part, plus $50 to $150 labor if a shop installs it. If wiring repairs or internal transmission work are needed, costs can rise significantly to $300 or more.

Q: Is P0939 the same as P0710 or P0711?

They are related but different codes. P0710, P0711, P0938, and P0939 all relate to transmission fluid or hydraulic oil temperature sensor faults, but they differ in whether the signal is high, low, or erratic, and which sensor circuit is affected. P0939 specifically indicates a low input signal on the hydraulic oil temperature sensor circuit. Always diagnose the specific code present rather than treating them interchangeably.

Abstract

Error code P0939 indicates that your vehicle's powertrain control module (PCM) has detected an abnormally low voltage or signal from the hydraulic oil temperature sensor — commonly found in automatic transmissions, CVTs, or hydraulic steering systems. This typically points to a faulty sensor, damaged wiring, or low/contaminated hydraulic fluid. While rated medium severity, ignoring it can lead to transmission overheating or poor shift quality, so it should be addressed promptly.