Fault code P0739 is called “TCM Engine Speed Output Circuit High” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.
Technical description and explained code P0739
If your OBD-II equipped vehicle has stored code P0739. This means that a fault has occurred in the engine speed output circuit in the Transmission Control Module (TCM).
The Transmission Control Module (TCM) operates similarly to the Engine Control Module (ECM). It monitors and regulates the functions of the transmission, while the ECM does the same thing, but with the engine.
The TCM uses signals from various sensors as well as ECM information to monitor, control, and regulate the transmission. In particular, the TCM uses the engine speed sensor (ESS) to determine shift timing.
The TCM controller activates code P0739 when it monitors one or more conditions outside a certain electrical range in the engine speed sensor or its circuit. Given the nature of the code and the location of the sensor, in most cases this will be an electrical problem.
A TCM engine speed output circuit error is set when the ECM monitors a general fault or high level in the engine speed output circuit.
Symptoms of vehicle malfunctions
The main signal that an error P0739 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.
It can also be warning signs such as:
- Check engine control lamp on the control panel will light up (the code will be recorded in the memory as a fault).
- Hard shifting of gears.
- Transmission refuses to shift.
- Emergency mode of transmission operation to avoid further damage.
- May have trouble starting the engine.
- Jerking/missing ignition at idle or under load.
- Speedometer may wobble or not work.
- Increased fuel consumption.
- Poor throttle response.
Diagnostic fault code P0739 varies from average to very serious, depending on the specific nature of the problem. The malfunction light may just be on, or the vehicle may not start at all.
Factors that can cause this error code
The error code P0739 can mean that one or more of the following problems have occurred:
- Engine speed sensor (ESS) is defective.
- Electrical circuits or connectors are open or short-circuited.
- Contaminated ESS sensor.
- Faulty shift solenoid.
- Contaminated transmission fluid restricting flow.
- Faulty PCM, TCM or other control module, also possible programming error.
How to fix or reset OBD-2 code P0739
Some suggested steps for troubleshooting and fix the error code P0739:
- Inspect the wiring for damage, abrasions, breaks, and shorts. If wiring is damaged, repair or replace it.
- Remove all diagnostic trouble codes from the PCM and perform a test drive to see if diagnostic trouble code P0739 returns.
- If the code returns, check the ESS sensor, replace if necessary.
- Clear the fault codes again and test drive.
- If the code returns, the PCM or TCM may need to be replaced and reprogrammed.
Diagnose and repair of problems
If your vehicle’s engine cranks normally but will not start, this may indicate a problem with the engine speed sensor (ESS) itself. Starting a diagnosis of fault P0739, check the sensor using the required electrical parameters from the manufacturer.
Repair or replace if necessary. Typically, these sensors read the crankshaft speed, so it will likely be mounted somewhere on the engine block.
Checking the fluid
Be sure to check the automatic transmission fluid. Make sure it is clean and filled to the level. Top up if necessary. Lack of fluid can cause automatic transmissions to not work properly.
Black or very dark transmission fluid must be replaced to ensure proper transmission operation. Low or dirty transmission fluid can not only cause this code to activate. Damage to internal transmission components can also occur.
Always use the transmission fluid recommended by the specific manufacturer for your make and model.
Inspection of wiring and sensor
Given the location of the ESS, wires can be subjected to friction and consequently frayed or damaged by road debris. Inspect them for damage. If the harness runs close to the engine and other sharp parts, a tear may occur.
Remove the ESS sensor from the cylinder block. It is magnetic and extremely sensitive to picking up debris or chips, which can potentially change electrical readings. After cleaning and clearing any debris, reinstall the sensor.
If error P0739 does not go away, inspect the transmission control module (TCM). These are often mounted directly to the transmission. This means that this electrical module may be operating in severe conditions. Look for any signs of corrosion, damage or any defects.
On which vehicles does this problem occur most frequently
Fault code P0739 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:
Fault code P0739 can sometimes be found with other errors. The most common are the following: P0613, P0737, P0738.