P1738 Code: Complete DIY Repair Guide

The P1738 code is a diagnostic trouble code (DTC) that indicates a problem in the 2nd clutch pressure switch circuit of the automatic transmission system. This code is commonly found in Honda and Acura vehicles, particularly in models from the late 1990s to early 2000s. When the Powertrain Control Module (PCM) detects an abnormal signal from the 2nd clutch pressure switch, it triggers the P1738 code and illuminates the check engine light.

Symptoms of P1738 Code

When your vehicle triggers the P1738 code, you may experience various symptoms related to transmission performance. It’s important to note that in some cases, there might be no noticeable symptoms other than the illuminated check engine light. However, common symptoms include:

1. Illuminated check engine light
2. Harsh or delayed gear shifts, especially involving 2nd gear
3. Transmission slipping
4. Reduced fuel efficiency
5. Decreased overall vehicle performance

If you notice any of these symptoms along with the P1738 code, it’s crucial to address the issue promptly to prevent further damage to your transmission system.

Technical Explanation of the P1738 Code

The P1738 code specifically relates to the 2nd clutch pressure switch circuit in the automatic transmission. This switch is responsible for monitoring the hydraulic pressure in the 2nd clutch of the transmission. The Powertrain Control Module (PCM) uses the information from this switch to determine when to engage or disengage the 2nd clutch, which is critical for proper gear shifting.

When the PCM detects an abnormal voltage or signal from the 2nd clutch pressure switch, it sets the P1738 code. This can happen if the switch itself is faulty, if there’s a problem with the wiring in the circuit, or if there’s an issue with the transmission fluid pressure affecting the switch’s operation.

Step-by-Step Diagnosis of P1738 Code

To diagnose the P1738 code, follow these steps:

1. Connect an OBD-II scanner to the vehicle’s diagnostic port and retrieve all stored codes and freeze frame data.
2. Check the transmission fluid level and condition. Low or degraded fluid can cause pressure-related issues.
3. Inspect the wiring and connectors related to the 2nd clutch pressure switch for any signs of damage, corrosion, or loose connections.
4. Use a digital multimeter to test the resistance of the 2nd clutch pressure switch. Compare the readings to the manufacturer’s specifications.
5. Check the voltage at the 2nd clutch pressure switch connector with the ignition on. You should see battery voltage.
6. If possible, use a scan tool to monitor the 2nd clutch pressure switch data while the transmission is shifting through gears.
7. Perform a visual inspection of the transmission for any signs of leaks or damage that could affect hydraulic pressure.
8. If all other components check out, consider testing the PCM or having it professionally diagnosed.

Solution Methods for P1738 Code

After diagnosing the issue, you can proceed with the following solutions:

1. Replace the 2nd clutch pressure switch:

• Locate the switch on the transmission (consult your vehicle’s service manual for exact location)
• Disconnect the electrical connector
• Remove the old switch using the appropriate socket or wrench
• Install the new switch, ensuring proper torque specifications
• Reconnect the electrical connector

1. Repair wiring issues:

• Identify any damaged, corroded, or frayed wires in the circuit
• Repair or replace the affected wiring
• Ensure all connections are clean and secure

1. Address transmission fluid issues:

• If the fluid level is low, add the appropriate type of transmission fluid
• If the fluid is degraded or contaminated, perform a transmission fluid flush and refill

1. PCM replacement or reprogramming:

• In rare cases where the PCM is at fault, it may need to be reprogrammed or replaced
• This should only be done after all other potential causes have been ruled out

Warning: Transmission work can be complex and may require specialized tools. If you’re not confident in your ability to perform these repairs, it’s best to consult a professional mechanic.

Cost Estimates for P1738 Code Repairs

The cost of repairing issues related to the P1738 code can vary depending on the root cause and your vehicle’s make and model. Here are some estimated costs:

1. 2nd clutch pressure switch replacement: $100 – $300
2. Wiring repair: $50 – $200
3. Transmission fluid service: $100 – $250
4. PCM replacement or reprogramming: $300 – $1000

These estimates include parts and labor. DIY repairs can significantly reduce costs, but ensure you have the necessary skills and tools before attempting transmission-related repairs.

Preventing P1738 Code Issues

To help prevent issues that could trigger the P1738 code:

• Regularly maintain your vehicle’s transmission, including fluid changes at recommended intervals
• Address any transmission-related symptoms promptly
• Avoid aggressive driving habits that could stress the transmission
• Use the correct type of transmission fluid specified for your vehicle

When to Seek Professional Help

While many P1738 code issues can be addressed by experienced DIY mechanics, there are situations where professional help is recommended:

• If you lack the necessary tools or experience to work on transmission components
• When diagnostic steps indicate internal transmission problems
• If multiple transmission-related codes are present
• When repairs require specialized equipment or software for PCM programming

Professional mechanics have the expertise and equipment to accurately diagnose and repair complex transmission issues, potentially saving you time and preventing further damage.

Conclusion

The P1738 code, while specific to the 2nd clutch pressure switch circuit, can be indicative of various transmission-related issues. By understanding the code’s meaning, potential causes, and diagnostic steps, you can approach the problem methodically. Whether you choose to tackle the repairs yourself or seek professional assistance, addressing the P1738 code promptly is crucial for maintaining your vehicle’s transmission health and overall performance.

Frequently Asked Questions About P1738

• Can I drive my car with the P1738 code?
  While the vehicle may still be drivable, it’s not recommended to continue driving with this code present. Doing so could lead to further transmission damage and potentially unsafe driving conditions.
• How urgent is it to address the P1738 code?
  It’s important to address this code as soon as possible. Transmission-related issues can worsen quickly and lead to more expensive repairs if left unattended.
• Will the P1738 code clear itself?
  The code may clear temporarily if the issue resolves, but it will likely return if the underlying problem isn’t fixed. Proper diagnosis and repair are necessary for permanent resolution.
• Can a bad battery cause the P1738 code?
  While unlikely, a weak battery could potentially cause erratic voltage readings that might trigger this code. However, it’s more likely to be a direct issue with the transmission or its components.
• Is the P1738 code covered under warranty?
  Coverage depends on your vehicle’s age, mileage, and specific warranty terms. Check your warranty documentation or consult with your dealer to determine if this repair is covered.
• How long does it take to fix a P1738 code issue?
  Repair time can vary from 1-3 hours for simple switch or wiring repairs to several days if internal transmission work is required. The exact time depends on the specific issue and repair method.
• Can I reset the P1738 code without fixing the problem?
  While you can clear the code temporarily, it will likely return if the underlying issue isn’t resolved. It’s not recommended to clear codes without addressing the root cause.
• Does the P1738 code affect fuel efficiency?
  Yes, it can. If the transmission isn’t operating correctly due to this issue, it may cause the engine to work harder, potentially reducing fuel efficiency.