The P1738 code is a manufacturer-specific powertrain code indicating a malfunction in the 2nd clutch transmission fluid pressure switch circuit. Because it is manufacturer-specific, its exact definition depends on the vehicle application.
This code identifies a detected electrical circuit condition, not necessarily a failed switch. Proper diagnosis requires verifying the exact factory definition and testing the relevant transmission circuit.
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Key Takeaways
- The P1738 code indicates a manufacturer-specific fault in the 2nd clutch transmission fluid pressure switch circuit.
- Possible causes include a failed pressure switch, damaged wiring harness, poor electrical connections, or low transmission fluid.
- Symptoms often include an illuminated Check Engine Light, harsh shifting, or delayed gear engagement.
- Diagnosis requires checking the transmission fluid condition and testing the switch circuit with a multimeter or scan tool.
- Repairs vary by application and may involve switch replacement, wiring repair, or fluid service.
P1738 Code Description and Implications
P1738 is a manufacturer-specific code. Its exact definition depends on the vehicle application.
Some Honda and Acura applications: The code relates to the 2nd clutch transmission fluid pressure switch circuit, indicating an electrical malfunction such as an open or short in the switch signal circuit.
Because this code involves transmission hydraulic control, addressing it promptly helps prevent drivability issues or further transmission wear.
Common Causes of the P1738 Code
Several conditions can trigger this transmission malfunction code. Identifying the exact cause requires electrical and hydraulic testing.
- Failed or internally shorted/open 2nd clutch transmission fluid pressure switch.
- Damaged, chafed, or broken wiring in the transmission switch harness.
- Corroded, loose, or fluid-contaminated electrical connectors at the transmission.
- Low or degraded transmission fluid affecting hydraulic pressure and switch operation.
- Faulty transmission control module or PCM (rare, usually only after circuit verification).
A faulty switch or harness issue can trigger this trouble code.
Symptoms Associated With P1738
Because this code involves transmission control, symptoms typically affect shifting and drivability.
- Illuminated Check Engine Light or specific transmission warning indicator.
- Harsh or delayed transmission shifting, particularly involving the 2nd gear clutch.
- Transmission slipping or entering a fail-safe mode on some applications.
- Decreased fuel efficiency due to improper clutch engagement.
Diagnosing the P1738 Trouble Code
Diagnosis must begin by confirming the exact factory definition and locating the specific pressure switch for your vehicle.
- Verify the exact manufacturer definition and locate the 2nd clutch pressure switch for your vehicle.
- Check the transmission fluid level and condition; low or burnt fluid can cause hydraulic and switch issues.
- Visually inspect the external transmission wiring harness and connectors for damage, corrosion, or fluid intrusion.
- Use a digital multimeter to measure the resistance or voltage of the suspect switch circuit and compare it to manufacturer specifications.
- Use a scan tool to monitor transmission data and verify switch state changes during gear commands.
Repairing the P1738 Issue
Repairs depend entirely on the confirmed root cause of the transmission circuit malfunction.
- If the pressure switch fails electrical or functional testing, replace the 2nd clutch transmission fluid pressure switch.
- If wiring damage is found, repair or replace the affected harness sections and seal the connections.
- Clean or replace corroded connectors to restore proper electrical contact.
- If the transmission fluid is low or degraded, perform a fluid and filter service according to manufacturer specifications.
- If testing confirms the PCM or TCM driver is faulty and all external circuits are intact, follow the manufacturer procedure for module replacement.
Cost Considerations for P1738 Repairs
Cost depends on diagnostic time, component accessibility, required parts, programming requirements, and labor.
Pressure switch replacement costs vary depending on whether the switch is externally mounted or requires transmission pan removal.
Prevention Strategies for Future Occurrences
While electrical failures are not always preventable, some practices can reduce the risk of transmission circuit issues.
- Maintaining proper transmission fluid levels and replacing fluid at manufacturer-recommended intervals helps prevent switch wear and hydraulic issues.
- Inspecting exposed transmission wiring and connectors can help identify developing damage from road debris or heat.
- Addressing minor transmission leaks promptly prevents fluid from contaminating electrical connectors.
Troubleshooting Tips and Best Practices
Always consult the exact manufacturer service information for your vehicle’s wiring diagram and switch pinout values.
- Do not assume the switch is faulty simply because the code points to its circuit; wiring and connector issues are frequently the actual cause.
- Check for related transmission codes that may indicate a broader hydraulic or electrical issue.
- Verify technical service bulletins for your specific make and model, as some manufacturers issue updated switches or software calibrations.
More OBD-II Codes
| P1727 | P1720 | P1718 | P1717 |
| P1716 | P1715 | P1739 | P1740 |
| P1745 | P1747 | P1753 | P1758 |
| P1762 | P1768 | P1773 | P1775 |
| P1777 | P1778 | P1780 | P1783 |
| P1788 | P1790 | P0700 | P0740 |
Frequently Asked Questions
Is the P1738 code generic or manufacturer-specific?
No. P1738 is a manufacturer-specific code. Its exact definition, such as a 2nd clutch pressure switch fault, depends entirely on the vehicle make and model.
Can I drive my car with a P1738 code?
You can drive the vehicle, but it is not recommended for long distances. A transmission pressure switch fault can cause harsh shifting, slipping, or improper clutch engagement.
Will changing the transmission fluid fix a P1738 code?
Changing the fluid may resolve the issue if low or degraded fluid caused the switch to malfunction. However, if the switch is electrically failed, a fluid change will not clear the code.
Can a bad pressure switch cause other transmission codes?
Yes. A failed pressure switch or hydraulic issue caused by a switch fault can trigger related transmission codes, such as gear ratio errors, slip codes, or other solenoid malfunctions.
Is it safe to reset the P1738 code without fixing it?
Clearing the code without repairing the underlying circuit or hydraulic fault is not a fix. The control module will continue to monitor the circuit, and the code will return once the monitor runs again.
What Should You Do About the P1738 Code?
Confirm the exact factory definition for your specific vehicle application. Follow the applicable manufacturer diagnostic procedure to test the relevant transmission pressure switch circuit, wiring, and fluid condition.
Repair or replace the confirmed failed component, then retest the system to ensure proper transmission operation.
