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 typically means the sensor is reading an abnormally low temperature or there is a short circuit to voltage. This can lead to incorrect transmission shift patterns, reduced fuel economy, or transmission damage if not addressed.
01. Most Common Causes
- Faulty hydraulic oil temperature sensor
- Short circuit to voltage in sensor wiring or connector
- Open circuit or high resistance in sensor ground circuit
- Corroded or damaged sensor connector
- Faulty PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission shifting harshly or erratically
- Reduced fuel economy
- Transmission may enter limp mode
- Overheating transmission fluid
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Visually inspect the hydraulic oil temperature sensor and wiring for damage, corrosion, or loose connections.
Step 3: Using a multimeter, check sensor resistance at various temperatures and compare to manufacturer specifications.
Step 4: Check for voltage at the sensor signal wire (should be 5V reference) and ground continuity.
Step 5: If sensor and wiring are OK, test PCM output and replace PCM if necessary.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances with this code as it can cause transmission damage. You may experience harsh shifting or limp mode. Have it diagnosed promptly.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and sensor replacement. Labor is usually 0.5-1 hour, and the sensor costs $20-$80.