P0738 TCM Engine Speed Output Circuit Low

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P0738 – OBD-II Trouble Code Technical Description
What does trouble code P0738 mean?
Possible reasons
What are the symptoms of trouble code P0738?
How to diagnose trouble code P0738?
Diagnostic errors
How serious is trouble code P0738?
What repairs will resolve the P0738 code?
P0738 – Brand Specific Information

P0738 – OBD-II Trouble Code Technical Description

TCM Engine Speed Output Circuit Low

What does the fault code mean P0738?

Code P0738 is a standard OBD-II trouble code that indicates a problem with the engine speed output sensor in the Transmission Control Module (TCM). This sensor monitors engine speed and transmits data to the powertrain control module (PCM), which uses this information to shift gears correctly. Typically, engine speed must vary in accordance with increasing vehicle speed to ensure smooth shifts. When the PCM detects that the engine speed is changing too quickly or not changing at all, it generates code P0738. This code can also be set if the PCM is not receiving a signal from the engine speed sensor.

Photo of the transmission control module:

The P0738 code is a universal OBD-II code that applies to various makes of vehicles including Dodge, Chevrolet, Honda, Toyota, Hyundai, Jaguar and many more. Although the code is common, the exact steps to resolve it may vary depending on the specific vehicle and its configuration.

Typically, P0738 is associated with electrical problems, more often than mechanical ones. However, the exact diagnostic and repair steps may require professional service and may vary depending on the make and model of vehicle.

Possible reasons

Potential causes of a P0738 code include:

Faulty engine speed sensor (ESS).
Faulty transmission output speed sensor.
Insufficient transmission fluid level.
Contaminated transmission fluid.
In rare cases, the engine control module (ECM) is faulty.
Defective electrical components including cables, connectors and fuses.

A P0738 code can be caused by a faulty Engine Speed Sensor (ESS), a faulty Engine Control Module (ECM), a faulty Transmission Control Module (TCM), wiring problems, dirty pickup at the Engine Speed Sensor (ESS), or connector problems. .

What are the symptoms of a fault code? P0738?

When a P0738 code appears, it is usually accompanied by the following symptoms:

Hard gear changes.
Reduced fuel consumption.
Problems with starting the engine.
Limited car speed.
The engine stalls or jerks.
Inaccurate speedometer display.
Less responsive throttle.

These symptoms may indicate transmission problems, including rough shifting, engine trouble, and speedometer display problems, which can ultimately lead to poor fuel economy.

How to diagnose a fault code P0738?

To diagnose and repair code P0738, it is recommended to follow these steps:

Use an OBD-II code scanner to diagnose the P0738 code and check for additional trouble codes.
If additional codes are detected, look at them in the order they appear on the scanner and resolve them starting with the first one.
After diagnosis, clear the trouble codes, restart the vehicle, and check if the P0738 code persists. If the code goes away after resetting and restarting, it may have been a temporary problem.
If the P0738 code persists, check the transmission fluid level and any leaks. Add fluid as needed and carefully check for leaks. Leaking fluid may cause further damage.
If the transmission fluid is dirty, replace it. If the fluid is excessively dirty, the transmission may need to be repaired or replaced.
Perform a visual inspection of electrical components. Replace damaged wires, connectors and fuses.
Check the output speed sensors, ensuring their signal ground and reference voltage are monitored.
After fixing the P0738 code, clear the trouble codes and restart the vehicle to see if the code goes away.

It's also important to consider technical service bulletins (TSBs) for your vehicle, as they may contain information about known problems and solutions. Repairing engine speed output circuits and systems may require special tools such as an OBD code reader, multimeter, and wiring tools. Be aware of safety precautions and ensure the integrity of the battery and charging system before working on electrical components.

Diagnostic errors

The most common mistake when diagnosing a P0738 code is not following the OBD-II trouble code diagnostic protocol. It is important that technicians always follow this protocol to avoid incorrect repairs. Otherwise, there is a risk of unnecessary replacements, such as a vehicle speed sensor or even a properly functioning output speed sensor. Diagnosis must be careful and methodical, starting with checking the basic elements and gradually moving to more complex components.

How serious is the fault code? P0738?

Trouble code P0738 can be serious because it indicates a problem with the transmission or engine speed sensor output signal. This can cause problems with gear shifting, which will ultimately lead to poor vehicle performance and possible transmission damage. Therefore, when the P0738 code appears, it is important to take steps to diagnose and repair the problem as soon as possible to prevent additional damage and costly repairs to the transmission.

What repair will help eliminate the code? P0738?

To resolve the P0738 code, a number of repairs are required, which may include:

Diagnosis: You must first perform diagnostics to determine the specific causes of the P0738 code. To do this, OBD-II fault code scanners are used.
Checking the transmission fluid: Check the level and condition of the transmission fluid. If the fluid level is low or contaminated, this may be the cause of the problem and may require topping up or replacing the fluid.
Speed Sensor Check: Check the transmission output shaft speed sensor for faults. Replace it if necessary.
Engine Speed Sensor (ESS) Check: Check the engine speed sensor for problems and replace it if necessary.
Inspect electrical components: Inspect wires, connectors, and fuses for damage. Replace them if they are damaged.
Cleaning and Replacement of Sensors: In some cases, cleaning the sensors and replacing them after removing any debris may solve the problem.
Transmission Control Module (TCM) Inspection: Check the TCM for corrosion, damage, or defects.
Software Update: In some cases, updating the TCM software may resolve the P0738 code.
Check for technical bulletins: Check to see if there are technical bulletins (TSBs) for your make and model of vehicle that may indicate known problems and solutions.

Remember that repairs will depend on the specific reasons why the P0738 code occurred. You should first carry out a diagnosis and then carry out the appropriate repair work depending on the identified problems.

What is P0738 Engine Code [Quick Guide]