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P1790 Toyota Code - ST Solenoid Valve Circuit Malfunction

Quick Answer

The P1790 diagnostic trouble code (DTC) for Toyota vehicles indicates a malfunction in the ST (starter) solenoid valve circuit. Common causes include Faulty ST solenoid valve, Corroded or damaged wiring in the solenoid valve circuit, Electrical issues, such as a blown fuse or relay. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
P1790 Toyota indicates ST Solenoid Valve Circuit Malfunction.
Common causes
Common causes include Faulty ST solenoid valve, Corroded or damaged wiring in the solenoid valve circuit, Electrical issues, such as a blown fuse or relay.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
What is this?
Table of contents Created and updated by William Orellana on Sep 07, 2024
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Code P1790 Toyota Description

The P1790 diagnostic trouble code (DTC) for Toyota vehicles indicates a malfunction in the ST (starter) solenoid valve circuit. The ST solenoid valve is an integral component of the transmission system, responsible for controlling the flow of hydraulic fluid that engages and disengages the starter clutch. When this valve malfunctions, it can lead to issues with starting the vehicle, shifting gears, and overall transmission performance.

OBDII Code P1790 Toyota - ST Solenoid Valve Circuit Malfunction
P1790 Toyota Code - ST Solenoid Valve Circuit Malfunction

Common Causes of P1790 Toyota

  1. Faulty ST solenoid valve
  2. Corroded or damaged wiring in the solenoid valve circuit
  3. Electrical issues, such as a blown fuse or relay
  4. Poor connection between the solenoid valve and the transmission control module
  5. Contaminated or degraded transmission fluid

Symptoms of P1790 Toyota

  1. Difficulty starting the vehicle
  2. Transmission slipping or shifting erratically
  3. Delayed engagement when shifting gears
  4. Illumination of the Check Engine Light
  5. Reduced fuel efficiency

How to Fix P1790 Toyota

  1. Diagnose the issue by using a scan tool to retrieve the specific DTC and inspecting the ST solenoid valve and its circuit for any visible damage.
  2. Test the solenoid valve's resistance to determine if it is functioning properly.
  3. Check the wiring and connections leading to the solenoid valve for any signs of damage or corrosion.
  4. Replace the ST solenoid valve if it is found to be faulty, ensuring proper installation and connection to the transmission system.
  5. Clear the DTC from the vehicle's onboard computer and test drive the vehicle to ensure the issue has been resolved.

Cost to Fix P1790 Toyota

The typical repair costs for addressing a P1790 ST Solenoid Valve Circuit Malfunction in a Toyota vehicle can vary depending on the extent of the issue and the specific parts needed for repair. In general, the cost of replacing a solenoid valve and addressing any related electrical or wiring issues can range from $200 to $500, including parts and labor. However, it is important to note that diagnosis time and labor rates at auto repair shops can vary significantly based on factors such as location, vehicle make and model, and the expertise of the technicians. It is recommended to consult with a qualified mechanic or auto repair shop to obtain a more accurate estimate for addressing this specific issue in your Toyota vehicle.

When is the Code Detected?

ECU memorizes DTC P1790 if (a) or (b) condition below is detected once or more, but ECU does not start MIL blinking.(a)Solenoid resistance is 30 W or lower (short circuit) when solenoid energized.(b) Solenoid resistance is 100 kW or higher (open circuit) when solenoid is not energized.

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Information for Specific Toyota Models

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

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