The P1790 trouble code is a diagnostic trouble code (DTC) that indicates a fault detected by the Transmission Control Module (TCM) immediately after a gear shift. This code is associated with the vehicle’s automatic transmission system and can lead to various performance issues, including erratic shifting, slipping, and even potential transmission damage if not addressed promptly. Understanding the implications of the P1790 code is crucial for vehicle owners and DIY mechanics who wish to maintain their vehicles in optimal condition.
| P1790 Code Meaning | P1790 Code Common Causes |
|---|---|
| Fault detected immediately after a gear shift | Faulty torque converter clutch solenoid |
| Transmission Control Module (TCM) checksum error | Damaged wiring or connectors |
| Transmission slipping or harsh shifting | Low or contaminated transmission fluid |
| Potential mechanical or hydraulic issues | Defective torque converter |
| Check engine light activation | Faulty transmission range sensor |
Symptoms of the P1790 Code
When the P1790 code is triggered, vehicle owners may experience a variety of symptoms, including:
- Check Engine Light: The most immediate indication is the illumination of the check engine light on the dashboard.
- Erratic Shifting: Drivers may notice irregular or harsh shifting between gears, which can affect overall driving comfort.
- Transmission Slippage: There may be instances where the transmission slips, leading to delayed acceleration or unexpected drops in speed.
- Reduced Fuel Efficiency: A decrease in fuel efficiency might occur due to suboptimal transmission performance.
- Limp Mode Activation: In severe cases, the vehicle may enter limp mode, limiting speed and power to prevent further damage.
Technical Explanations
The P1790 code typically arises when the TCM detects a fault immediately after a shift. This could be due to several factors:
- Torque Converter Clutch Solenoid: This solenoid regulates fluid flow to the torque converter. If it fails, it can lead to improper engagement of the clutch, causing shifting issues.
- Wiring Issues: Damaged or corroded wiring can disrupt signals between the TCM and other components, leading to erroneous readings and performance problems.
- Fluid Levels: Low or contaminated transmission fluid can lead to inadequate lubrication and cooling, resulting in increased wear on transmission components.
- Mechanical Failures: Worn or damaged components within the transmission system can also trigger this code.
Step-by-Step Diagnosis
Diagnosing the P1790 code involves several systematic steps:
- Use an OBD-II Scanner: Connect an OBD-II scanner to retrieve the P1790 code and check for any additional codes that may provide more context.
- Inspect Transmission Fluid: Check both the level and condition of the transmission fluid. It should be at the recommended level and have a clean, reddish color. Contaminated or burnt fluid should be replaced.
- Examine Wiring and Connectors: Inspect all wiring related to the TCM and solenoids for signs of wear, damage, or corrosion.
- Test Torque Converter Clutch Solenoid: Verify that the solenoid is functioning correctly using a multimeter or by observing its operation during a road test.
- Check Transmission Range Sensor: Ensure that this sensor is providing accurate readings as it plays a critical role in shift timing.
- Perform a Road Test: After completing inspections and repairs, conduct a road test to observe how well the transmission shifts under various conditions.
- Consult Vehicle Service Manual: For specific procedures related to your vehicle make and model, refer to the service manual for guidance on diagnostics and repairs.
Solution Methods
Addressing the P1790 code requires targeted repairs based on diagnosis:
- Replace Torque Converter Clutch Solenoid: If diagnosed as faulty, replacing this solenoid can resolve shifting issues linked to this code.
- Repair Wiring Issues: Damaged wiring should be repaired or replaced as necessary to restore proper signal flow between components.
- Change Transmission Fluid: If fluid quality is compromised, draining and replacing it with fresh fluid can improve performance significantly.
- Replace Torque Converter: In cases where mechanical failure is identified within the torque converter itself, replacement may be necessary.
- Reprogram TCM if Needed: Sometimes, updating or reprogramming the TCM software can resolve communication issues that trigger this code.
Cost Estimates
The cost of repairs associated with P1790 can vary widely based on several factors:
- Replacing a torque converter clutch solenoid typically ranges from $100 to $300 in parts and labor.
- Repairing wiring issues may cost between $50 and $150 depending on accessibility.
- A complete fluid change can range from $100 to $200 depending on whether additional services are performed.
- Replacing a torque converter can be more expensive, often ranging from $600 to $1,200 including parts and labor.
It’s essential to obtain quotes from multiple repair shops for accurate estimates tailored to your specific situation.
Warnings and Recommendations
- Always address P1790 codes promptly; neglecting them can lead to severe transmission damage and costly repairs.
- If you are not comfortable performing these diagnostics or repairs yourself, seek professional assistance from an ASE-certified technician.
- Regular maintenance of your vehicle’s transmission system—including fluid changes—can help prevent issues that trigger DTCs like P1790.
Closing Paragraph
The P1790 trouble code signifies critical issues within your vehicle’s transmission system that require immediate attention. By understanding its causes, symptoms, and solutions, vehicle owners can take proactive steps towards diagnosing and resolving these problems effectively. Whether you’re a DIY mechanic or someone who prefers professional help, being informed about this DTC will empower you to maintain your vehicle better and ensure safe driving conditions.
Frequently Asked Questions About P1790
- What does the P1790 code mean?
The P1790 code indicates a fault detected by the Transmission Control Module (TCM) immediately after a gear shift. - Can I drive my car with a P1790 code?
While it is possible to drive with this code active, it is not recommended as it may lead to further transmission damage. - What are common symptoms of P1790?
Common symptoms include erratic shifting, check engine light activation, reduced fuel efficiency, and potential limp mode activation. - How do I diagnose a P1790 code?
Diagnosis involves using an OBD-II scanner, inspecting transmission fluid levels, checking wiring integrity, testing solenoids, and performing road tests. - What are potential fixes for a P1790 code?
Fixes include replacing faulty solenoids or wiring, changing contaminated fluid, or replacing damaged components like the torque converter. - Is it safe to ignore a P1790 code?
No; ignoring this code can lead to severe transmission problems that may result in costly repairs. - How much does it cost to fix a P1790 code?
The cost varies widely but can range from $100 for minor repairs up to over $1,200 for major component replacements. - When should I seek professional help for a P1790 code?
If you are uncomfortable performing diagnostics or repairs yourself or if multiple codes are present, it’s best to consult a professional mechanic.