P1738 – OBD-II DTC

OBD-II DTC P1738 – 3-4 Shift Malfunction

DTC P1738 meaning

DTC P1738 refers to a diagnostic trouble code indicating a malfunction in the 3-4 shift of the transmission. This code is specific to automatic transmissions and suggests that the transmission control module (TCM) has detected an issue when attempting to shift from third gear to fourth gear. The problem may stem from various factors, including mechanical failures, electrical issues, or sensor malfunctions.

DTC P1738 symptoms

Common symptoms associated with DTC P1738 may include:

• Delayed or harsh shifting between gears
• Inability to shift into fourth gear
• Transmission slipping or erratic behavior
• Check Engine Light illuminated
• Unusual noises from the transmission

DTC P1738 causes

Several potential causes for DTC P1738 include:

• Faulty transmission control module (TCM)
• Worn or damaged transmission components
• Malfunctioning shift solenoids
• Low transmission fluid levels or contamination
• Electrical issues such as damaged wiring or connectors
• Faulty input or output speed sensors

DTC P1738 seriousness

The seriousness of DTC P1738 can vary. While it may not cause immediate safety concerns, it can lead to further transmission damage if not addressed. Prolonged driving with this code may result in more severe transmission issues, increased repair costs, and potential vehicle breakdowns. It is advisable to diagnose and repair the issue promptly to maintain vehicle performance and reliability.

How to diagnose DTC P1738

To diagnose DTC P1738, follow these steps:

1. Use an OBD-II scanner to confirm the presence of the P1738 code.
2. Check for any additional trouble codes that may provide more context.
3. Inspect the transmission fluid level and condition.
4. Examine the wiring and connectors related to the transmission for damage or corrosion.
5. Test the operation of the shift solenoids and sensors.
6. Perform a road test to observe shifting behavior and identify any irregularities.

How to fix DTC P1738 step-by-step instructions

To fix DTC P1738, follow these step-by-step instructions:

1. Address any low or contaminated transmission fluid by replacing it and ensuring proper levels.
2. Repair or replace any damaged wiring or connectors related to the transmission.
3. Test and replace faulty shift solenoids if necessary.
4. Inspect and replace any worn or damaged transmission components.
5. Replace faulty input or output speed sensors as needed.
6. Clear the DTC using an OBD-II scanner and perform a road test to verify the fix.

How to erase DTC P1738

To erase DTC P1738, follow these steps:

1. Connect an OBD-II scanner to the vehicle’s diagnostic port.
2. Turn on the ignition without starting the engine.
3. Access the scanner’s menu and select the option to clear or erase trouble codes.
4. Confirm the action and wait for the scanner to complete the process.
5. Disconnect the scanner and start the vehicle to check if the code reappears.

Recommended tools for OBD-II diagnostics

Explore our expert picks: The Best OBD2 Scanners for 2025

Easy-to-use Multimeter for reliable diagnostics: AstroAI Auto-ranging Multimeter

Some of the links on this page may be affiliate links, which means we may earn a small commission if you make a purchase. This helps us keep our DTC database up to date and provide valuable content for free. We only recommend products that we have tested and believe to be the best in their class.