DTC Code P1790 – What does this code mean?

<ul> <li><b>Engine Light ON</b>: The engine light illuminates on the dashboard, indicating a fault in the transmission system. This is often linked to issues detected immediately after a gear shift.</li> <li><b>Erratic Shifting</b>: The vehicle may experience irregular or harsh shifting between gears. This can be caused by transmission control module (TCM) errors or issues with the shift solenoids.</li> <li><b>Transmission Slippage</b>: The transmission may slip, causing a delay in acceleration or a sudden drop in speed. This can be due to low transmission fluid levels or worn-out clutch components.</li> <li><b>Reduced Fuel Efficiency</b>: A noticeable decrease in fuel efficiency may occur due to the transmission not operating optimally. This can be a result of internal transmission faults or sensor malfunctions.</li> </ul>

<ul><li>The transmission has an internal mechanical problem, which could involve worn or damaged components affecting shift quality.</li><li>Faulty or malfunctioning transmission control module (TCM) that fails to properly manage gear shifts.</li><li>Issues with the transmission fluid, such as low levels or contamination, leading to improper lubrication and shifting.</li><li>Problems with the shift solenoids, which control the flow of transmission fluid and can cause erratic shifting if malfunctioning.</li><li>Electrical issues, such as damaged wiring or poor connections, affecting the transmission's ability to shift correctly.</li></ul>

<ul> <li><b>Initial Scan</b>: Use an OBD-II scanner to confirm the presence of DTC P1790 and check for any additional codes that may be related.</li> <li><b>Inspect Transmission Fluid</b>: Check the transmission fluid level and condition. Low or dirty fluid can cause shifting issues.</li> <li><b>Check Transmission Control Module (TCM)</b>: Inspect the TCM for any signs of damage or corrosion. Ensure all connections are secure.</li> <li><b>Test Transmission Range Sensor</b>: Verify the operation of the transmission range sensor using a multimeter. Ensure it is providing accurate readings.</li> <li><b>Inspect Wiring and Connectors</b>: Examine the wiring and connectors related to the transmission system for any signs of wear, damage, or corrosion.</li> <li><b>Perform a Road Test</b>: Conduct a road test to observe the transmission's behavior during shifts. Note any irregularities or delays.</li> <li><b>Check for Software Updates</b>: Verify if there are any software updates available for the TCM that may address the issue.</li> <li><b>Consult Service Manual</b>: Refer to the vehicle's service manual for specific diagnostic procedures and specifications related to DTC P1790.</li></ul>

<p>The DTC code P1790 indicates a fault immediately after a shift, which is critical for vehicle operation. <ul><li><b>Immediate Actions:</b> Inspect the transmission control module (TCM) and related sensors.</li><li>Check for any transmission fluid issues or mechanical failures.</li></ul> Delayed repair can lead to severe transmission damage, resulting in costly repairs and potential vehicle immobility.</p>