P0790 Transmission mode select switch circuit malfunction

P0790 – OBD-II Trouble Code Technical Description

Trouble code P0790 The PCM has detected a malfunction in the transmission mode switch circuit. 

What does trouble code P0790 mean?

Trouble code P0790 indicates a detected fault in the vehicle's transmission selector circuit. This means that the vehicle's control system has detected a problem with the mechanism or electrical connection associated with switching transmission modes. The switch, system wiring and connectors, and mode drive are included in this diagram.

Possible reasons

Some of the possible causes of the P0790 trouble code are:

• Defective transmission mode switch.
• Problems with system wiring or connectors associated with the transmission mode switch.
• There is a malfunction in the transmission mode switching mechanism itself.
• Problems with the PC (programmable engine control module) or other components related to switching transmission modes.
• Electrical noise or short circuit in the transmission mode switch circuit.
• Inconsistency of signals from the transmission mode switch with the expected values ​​in the PC.

These causes may require more detailed diagnostics to pinpoint the root of the problem.

What are the symptoms of a fault code? P0790?

Symptoms for a P0790 trouble code can vary depending on the specific problem and vehicle design, some of the potential symptoms are:

• Unsuccessful attempts to switch transmission modes.
• Lack of response to attempts to switch transmission modes.
• Problems with automatic gear shifting.
• “Check Engine” error or warning on the instrument panel.
• Incorrect display of the selected transmission mode on the dashboard.
• Various problems with the correct operation of the gearbox.

If these symptoms occur, especially in conjunction with the P0790 trouble code, it is recommended that you contact a professional auto mechanic for diagnosis and repair.

How to diagnose a fault code P0790?

The following steps are recommended to diagnose DTC P0790:

1. Using a Diagnostic Scanner: First, you should connect the diagnostic scanner to the vehicle's OBD-II port and read the trouble codes. This will help determine the presence of the P0790 code and any other related codes.
2. Checking Electrical Connections: Perform a visual inspection of the electrical connections associated with the transmission mode switch. Make sure the connections are secure and there is no damage to the wires or corrosion.
3. Checking the transmission mode switch: Check the transmission mode switch itself for damage, corrosion or wear. Check its operation to make sure it shifts correctly.
4. Control system diagnostics: Carry out additional tests and diagnostics of the control system to eliminate possible malfunctions in the PC or other components associated with switching transmission modes.
5. Using testers or a multimeter: If necessary, you can use a tester or multimeter to check the electrical signals and voltages in the transfer mode switch circuit.
6. Finding More Information: If necessary, refer to the technical documentation or repair manual for your specific vehicle make and model for additional instructions on diagnosing the P0790 trouble code.

If you are unsure of your diagnostic skills, it is recommended that you consult a qualified auto mechanic.

Diagnostic errors

When diagnosing DTC P0790, the following errors may occur:

1. Misinterpretation of the code: Sometimes mechanics may misinterpret the code and assume that the problem is solely related to the transmission mode switch, missing other potential causes.
2. Faulty Component Replacements: Because the code indicates a fault in the transmission switch circuit, mechanics may be tempted to replace the switch itself without performing a full diagnosis, which could result in replacing a functional component.
3. Skipping Wiring and Connector Diagnosis: Some mechanics may skip diagnosing electrical wiring and connectors, which could also be causing the problem.
4. Incomplete Diagnosis: Sometimes mechanics may skip additional tests such as checking circuit voltage, using a multimeter to test signals, etc., which can result in an incomplete diagnosis of the problem.
5. Incorrect Calibration: If a component is replaced or repair work is carried out, it is necessary to ensure that the system is correctly calibrated to avoid further problems.

To avoid these errors, it is important to follow a professional diagnostic technique, perform a complete check of all components, and pay attention to every detail when troubleshooting the problem.

How serious is the fault code? P0790?

Trouble code P0790 is serious because it indicates a problem in the transmission mode switch circuit. This switch is essential for proper transmission function and gear shifting, which is critical to the safety and proper operation of the vehicle. If the problem is not corrected, this may result in the transmission not operating correctly, making it impossible to shift gears correctly, which in turn can lead to poor handling and safety of the vehicle. Therefore, it is recommended that you immediately contact a qualified auto mechanic for diagnosis and repair.

What repair will help eliminate the code? P0790?

To resolve DTC P0790, the following repairs must be performed:

1. Replacing the transmission mode switch: If diagnostics have confirmed that the transmission mode switch is faulty, it is recommended to replace it with a new or working one. Before replacing the switch, ensure that the component is properly diagnosed and confirmed to be faulty.
2. Checking and replacing wiring and connectors: If damage, corrosion or breaks are found in the electrical wiring or connectors, they must be repaired or replaced. Incorrect connections or breaks can result in insufficient contact and a P0790 code.
3. Diagnosis and repair of the mode drive: If the problem is related to the mode drive, it is necessary to conduct additional diagnostics and perform the appropriate repair or replacement of the drive.
4. Checking and updating software: Sometimes problems with electrical components can be caused by bugs in the software. In such cases, it is recommended to check for software updates for the control modules and update them.
5. Re-Diagnosis and Testing: After repairs have been completed, you should re-diagnose using the diagnostic scanner to ensure that there is no P0790 code or other related errors.

It is important to contact a qualified auto mechanic or auto repair shop to perform professional repairs and diagnostics, especially if you do not have sufficient experience or knowledge in this area.

How to Diagnose and Fix P0790 Engine Code - OBD II Trouble Code Explain

P0790 – Brand-specific information

Trouble code P0790 can be found in different brands of cars, and its meaning may vary slightly depending on the specific brand, some of the meanings of the P0790 code for different brands:

1. Ford: P0790 – Transmission mode select switch – circuit malfunction.
2. Chevrolet / GMC: P0790 – Electrical fault in the transmission mode solenoid valve.
3. Toyota: P0790 – Transmission mode selector switch – circuit malfunction.
4. Honda/Acura: P0790 – Transmission mode select switch – circuit malfunction.
5. Nissan/Infiniti: P0790 – Invalid transmission mode shift signals.
6. Volkswagen/Audi: P0790 – Transmission mode select switch – circuit malfunction.
7. BMW: P0790 – Transmission mode switch: short circuit.
8. Mercedes-Benz: P0790 – Gear mode switch malfunction.

These are just a few examples, and the actual meaning may vary depending on the specific model and year of the vehicle. It is recommended that you consult the official repair or diagnostic manuals for your specific vehicle brand for more accurate information about the P0790 trouble code.