Hydraulic Oil Temperature Sensor Circuit High
The P0940 code indicates that the Powertrain Control Module (PCM) has detected a voltage signal from the hydraulic oil temperature sensor that is higher than the expected range. This sensor monitors the temperature of the hydraulic fluid in automatic transmissions or power steering systems. A high voltage reading typically means the sensor is reporting an abnormally low temperature or there is a short circuit to voltage in the wiring. This can lead to incorrect transmission shift patterns or reduced power steering assist.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission shifting erratically or stuck in gear
- Reduced fuel economy
- Power steering assist issues (if applicable)
- Transmission overheating
2. Most Common Causes
- Faulty hydraulic oil temperature sensor
- Short circuit to voltage in sensor wiring
- Open circuit or high resistance in sensor ground
- Corroded or damaged connector
- Faulty PCM (rare)
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve the code and freeze frame data.
Step 2: Visually inspect the sensor and wiring for damage, corrosion, or loose connections.
Step 3: Measure the sensor resistance and compare to manufacturer specifications (typically 100k ohms at cold, 1k ohms at hot).
Step 4: Check for voltage at the sensor signal wire (should be 5V reference from PCM).
Step 5: If sensor and wiring are good, test the PCM output or replace the sensor.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as it can cause transmission damage or overheating. Short trips to a repair shop are acceptable if the transmission is not slipping.
How much does it cost to fix?▼
The typical repair cost ranges from $50 to $150 for sensor replacement, plus diagnostic fees. Labor is usually 0.5-1 hour.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.