P0739 - TCM Engine Speed Output Circuit High
The P0739 code indicates that the Transmission Control Module (TCM) has detected a high voltage or signal in the engine speed output circuit. This circuit is responsible for communicating engine RPM data to the TCM for proper shift timing and torque converter lockup. A high signal can result from a faulty engine speed sensor, wiring issues, or a malfunctioning TCM, leading to erratic transmission behavior.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Erratic shifting or transmission slipping
- Harsh or delayed gear engagement
- Reduced fuel economy
2. Most Common Causes
- Faulty engine speed (RPM) sensor
- Short to voltage in the engine speed sensor circuit
- Damaged wiring or connectors in the sensor circuit
- Faulty TCM (less common)
3. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for additional codes.
Step 2: Visually inspect the engine speed sensor and its wiring for damage, corrosion, or loose connections.
Step 3: Test the sensor's voltage and resistance with a multimeter; compare to manufacturer specifications.
Step 4: If sensor and wiring are okay, test the TCM for proper operation or check for software updates.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the transmission may shift erratically or fail, potentially causing further damage.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and sensor replacement, but can be higher if the TCM needs replacement.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.