P0739 - TCM Engine Speed Output Circuit High
The P0739 code indicates that the Transmission Control Module (TCM) has detected a high voltage condition in the engine speed output circuit. This circuit is responsible for communicating engine RPM data from the Engine Control Module (ECM) to the TCM for proper transmission shift scheduling. A high voltage reading can be caused by a faulty sensor, wiring issues, or a malfunctioning TCM or ECM. This condition can lead to erratic shifting, poor fuel economy, and potential transmission damage if not addressed.
01. Most Common Causes
- Faulty engine speed sensor (crankshaft position sensor)
- Short to voltage in the engine speed signal circuit
- Damaged wiring or connectors in the TCM/ECM circuit
- Malfunctioning TCM or ECM
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Erratic or harsh transmission shifting
- Transmission stuck in a single gear (limp mode)
- Decreased fuel economy
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for additional related codes.
Step 2: Inspect the engine speed sensor and its wiring for damage, corrosion, or shorts to voltage.
Step 3: Test the engine speed sensor signal with a multimeter or oscilloscope to verify proper voltage and waveform.
Step 4: Check the TCM and ECM for any software updates or known issues; perform a circuit continuity test.
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. The vehicle may enter limp mode, limiting speed and drivability.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and repair, depending on the root cause. Sensor replacement may cost more if needed.