Technical Description of OBD-II Trouble Code
High Circuit Output of TCM Engine Speed
What does that signify?
This is a generic diagnostic trouble code (DTC) for powertrain and is applicable to OBD-II vehicles. This includes vehicles from various manufacturers such as Dodge, Chevrolet, Honda, Toyota, Hyundai, Jaguar, etc. Although it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
The TCM (Transmission Control Module) functions similarly to the ECM (Engine Control Module) as it monitors, controls, and regulates the transmission’s functions, while the ECM does the same for the engine.
The TCM utilizes different sensors, switches, and the ECM to monitor, control, and regulate the drivability of the transmission. One of its key functions is using an Engine Speed Sensor (ESS) to determine shift points. As the name suggests, the ESS monitors the engine’s speed. It may also be referred to as CKP (Crankshaft Position Sensor) or OSS (Output Speed Sensor).
Most of the time, a hall effect type sensor is used to measure the speed of the crankshaft. The sensor detects notches in the flywheel as they pass through, allowing it to monitor the crankshaft’s position. It is crucial for the ECM and TCM to have an accurate reading from this sensor as it affects various aspects such as shift points, speed, and drivability.
The ECM triggers the P0739 code and related codes when it detects one or multiple conditions outside the specific electrical range within the Engine Speed Sensor or its circuit. Considering the nature of the code and the sensor’s location, it is likely that this is an electrical issue. Mechanical issues causing this code are relatively rare.
The P0739 code is set when the ECM detects a higher than desired specific electrical value within the Engine Speed output circuit(s).
What is the severity of this DTC?
In terms of severity, I would classify it as low. However, this may vary depending on the specific situation. Generally, this fault only leads to drivability issues. Nevertheless, continued use with this fault may result in long-term consequences, so it is important to monitor it closely.
Photo of a transmission control module:
What are some of the symptoms of the code?
The symptoms of a P0739 trouble code may include:
What are some of the common causes of the code?
The causes of this P0739 transmission code may include:
What are some P0739 troubleshooting steps?
Make sure to check for any technical service bulletins (TSBs) related to your vehicle. Accessing a known fix can save time and money during the diagnosis process.
Tools
Some of the tools you may need when diagnosing or repairing engine speed output circuits and systems include:
Safety Tips
NOTE: ALWAYS verify and record the integrity of your battery and charging system before proceeding with further troubleshooting.
Basic Step #1
If your car’s engine cranks fine but does not start, it may indicate a problem with the ESS (Engine Speed Sensor) itself. Test the sensor using the electrical values specified by the manufacturer. Repair or replace as necessary. Typically, these sensors are mounted somewhere on the engine block and read the speed of the crankshaft.
Basic Step #2
Check your fluids. Ensure that you inspect the automatic transmission fluid and make sure it is clean and at the proper level. Top up as needed. Low fluid levels can cause unusual behavior in automatic transmissions, so it is important to address this issue. If the transmission fluid is black or extremely dark, it should be replaced to ensure proper transmission function. Low and/or dirty transmission fluid not only triggers this code, but it can also cause further damage to internal transmission components, which can be a costly repair. Therefore, it is crucial to have clean and adequate fluid.
NOTE: Always use the transmission fluid recommended by the manufacturer for your specific make and model. Using the wrong fluid can lead to significant problems. Do thorough research!
Basic Step #3
Inspect the wiring. Due to the ESS’s location, the wires are exposed to the elements and road debris. Check for any damage to the wiring harness. Chafing may occur if the harness is routed too close to the engine or other sharp components. Repair any damaged wiring.
NOTE: Consult your service manual to ensure proper identification of the desired wiring harness.
Basic Step #4
Clean the sensor. Removing the ESS may be relatively simple. If possible, remove the sensor from the engine block. Inspect the sensor’s pickup, as it is magnetic and highly susceptible to collecting debris or shavings that can affect the electrical readings. Once cleaned and free of debris, reinstall the sensor.
Basic Step #5
Inspect the TCM (Transmission Control Module). In many cases, it is mounted directly on the transmission, exposing it to harsh conditions. Therefore, check for any signs of corrosion, damage, or defects.
