P0938
UniversalHydraulic Oil Temperature Sensor Range/Performance
Medium SeverityThe P0938 code indicates that the vehicle's computer has detected an issue with the Hydraulic Oil Temperature Sensor or its circuit, reporting readings that are outside of the expected operating range or performing erratically. This often means the transmission control module (TCM) cannot accurately monitor the transmission fluid temperature, which can impact proper shifting and transmission operation.
⚠️ Before You Begin (Safety First)
Always exercise caution when working on a vehicle, especially when dealing with hot fluids or electrical systems. Ensure the engine is off and cool, and disconnect the battery before attempting any repairs. Transmission fluid can be hot and cause burns. Use proper jack stands and safety gear.
Common Symptoms
- Check Engine Light illuminated
- Erratic or harsh shifting
- Transmission slipping
- Delayed engagement of gears
- Transmission possibly entering 'limp mode'
- Overheating transmission (less common, but possible if sensor is faulty)
Common Causes
- Faulty Hydraulic Oil Temperature Sensor
- Damaged or corroded wiring to the sensor
- Loose or corroded electrical connectors
- Low or contaminated transmission fluid
- Internal transmission mechanical issues (less common, but can affect sensor readings)
- Faulty Transmission Control Module (TCM) (rare)
Frequently reported on: Ford F-150 (2009-2014), Ram 1500 (2012-2018), Chevrolet Silverado (2007-2013), Jeep Grand Cherokee (2011-2015)
Diagnostic Steps
- Check transmission fluid level and condition; top off or replace if necessary.
- Visually inspect the wiring harness and connectors leading to the Hydraulic Oil Temperature Sensor for any signs of damage, corrosion, or loose connections. Repair as needed.
- If accessible, disconnect the sensor and test its resistance using a multimeter, comparing readings to manufacturer specifications. Ensure the sensor circuit has proper voltage and ground.
- Clear the P0938 code using an OBD-II scanner and test drive the vehicle to see if the code returns.
- If the sensor tests faulty or the code immediately returns after clearing, replace the Hydraulic Oil Temperature Sensor.
- Recheck fluid levels and re-evaluate transmission performance.
👨🔧 When to Call a Professional
If after inspecting the wiring and checking fluid levels, the issue persists, or if you notice significant transmission performance degradation such as slipping, harsh shifts, or unusual noises, it's best to consult a professional transmission specialist. Internal transmission sensor replacement often requires specialized tools and knowledge.
Commonly Asked Questions
What does the Hydraulic Oil Temperature Sensor do?
The Hydraulic Oil Temperature Sensor monitors the temperature of the transmission fluid and sends this data to the Transmission Control Module (TCM), which uses it to adjust shifting strategies, line pressure, and torque converter lock-up for optimal performance and longevity.
Can I drive with code P0938?
While you might be able to drive, it's not recommended for extended periods. The TCM may not be able to properly manage transmission functions, potentially leading to erratic shifting, increased wear, or even transmission damage over time. It's best to diagnose and repair it promptly.
Where is the Hydraulic Oil Temperature Sensor located?
Its location varies by vehicle, but it's typically found within the transmission assembly. It might be located inside the transmission oil pan (requiring removal of the pan) or externally on the transmission case.
How can I test the Hydraulic Oil Temperature Sensor?
You can usually test the sensor's resistance using a multimeter. Compare the readings to the specific resistance-to-temperature chart provided in your vehicle's service manual. An 'open' or 'short' circuit will also indicate a faulty sensor.
What if replacing the sensor doesn't fix the P0938 code?
If the sensor replacement doesn't resolve the issue, the problem might be in the wiring harness or connectors leading to the sensor, or less commonly, with the Transmission Control Module (TCM) itself. A thorough wiring inspection and continuity test would be the next step.