How to Tell If MDS Solenoid is Bad?

The MDS (Multiple Displacement System) solenoid is an essential component in modern engines that helps improve fuel efficiency. However, like any other mechanical part, it can fail over time.

In this article, we will discuss how to tell if an MDS solenoid is bad and the steps to address the issue.

What is an MDS Solenoid?

Before diving into the signs of a bad MDS solenoid, it’s important to understand its function. The MDS solenoid is responsible for controlling the flow of oil to activate or deactivate specific engine cylinders. By deactivating cylinders when not needed, the engine can conserve fuel and improve efficiency. This is especially common in vehicles equipped with a V8 engine.

Symptoms of a Bad MDS Solenoid

When the MDS solenoid starts to fail, several symptoms may arise. It’s crucial to pay attention to these signs to diagnose and rectify the issue promptly.

Engine Misfires

One of the most noticeable signs of a faulty MDS solenoid is engine misfire. Misfires occur when the solenoid fails to deactivate specific cylinders, leading to a disruption in the combustion process. You may experience rough running, hesitation, or a loss of power while driving.

Decreased Fuel Efficiency

A bad MDS solenoid can negatively impact your vehicle’s fuel efficiency. Since the solenoid is responsible for deactivating cylinders when not needed, a malfunctioning solenoid may fail to deactivate cylinders, resulting in higher fuel consumption. If you notice a sudden drop in your vehicle’s mileage, it could be a sign of a bad MDS solenoid.

See also  Toyota RAV4’s ‘HOLD’ Button

Rough Idling

A faulty MDS solenoid can cause rough idling in your vehicle. You may experience vibrations or shaking while the engine is running at idle speed. This can be due to improper cylinder deactivation, resulting in an imbalance within the engine.

Illuminated Check Engine Light

In many cases, a bad MDS solenoid triggers the check engine light on your vehicle’s dashboard. The engine control unit (ECU) detects the irregularities in cylinder activation and deactivation and registers diagnostic trouble codes (DTCs). When the check engine light illuminates, it’s advisable to have your vehicle diagnosed to identify the specific issue.

Testing the MDS Solenoid

If you suspect a bad MDS solenoid, several methods can help you confirm the problem before replacing the component.

Visual Inspection

Start with a visual inspection of the solenoid. Look for any signs of damage, such as loose connections, frayed wires, or oil leaks. If you notice any visible issues, it’s likely that the solenoid needs replacement.

Diagnostic Trouble Codes (DTCs)

Using an OBD-II scanner, you can retrieve the DTCs stored in your vehicle’s ECU. DTCs related to the MDS system can provide valuable information about the solenoid’s condition. Take note of the specific codes and consult the vehicle’s service manual or an automotive professional to interpret them accurately.

Using a Scan Tool

Modern vehicles are equipped with advanced scan tools that can perform specific tests on the MDS solenoid. These tools can activate or deactivate the solenoid and monitor its response. If the solenoid fails to perform as expected or shows erratic behavior, it indicates a malfunction.

See also  How to Set Pinion Angle on Lowered Truck?

Professional Assistance

If you’re uncertain about performing the tests yourself or lack the necessary tools, it’s recommended to seek professional assistance. Automotive technicians have the expertise and specialized equipment to diagnose and address MDS solenoid issues accurately.

Replacing a Faulty MDS Solenoid

If the tests confirm a bad MDS solenoid, you can follow these general steps to replace it. However, it’s important to consult the vehicle’s service manual for specific instructions related to your make and model.

  1. Gather the necessary tools, including a wrench, socket set, and new solenoid.
  2. Locate the MDS solenoid, which is typically positioned on the engine block.
  3. Remove the electrical connector and any mounting bolts securing the solenoid.
  4. Carefully extract the old solenoid, ensuring not to damage any surrounding components.
  5. Install the new solenoid in the reverse order of removal, connecting the electrical connector and securing it with the mounting bolts.
  6. Double-check all connections and ensure everything is properly tightened.
  7. Start the vehicle and perform a test drive to ensure the issue has been resolved.


In conclusion, the MDS solenoid plays a vital role in optimizing fuel efficiency in modern engines. Understanding the symptoms of a bad MDS solenoid and how to test and replace it can help you maintain the performance and efficiency of your vehicle. If you encounter any signs of a failing solenoid, it’s essential to address the issue promptly to prevent further damage and ensure optimal engine performance.


1. Can a bad MDS solenoid damage the engine?

No, a bad MDS solenoid itself is unlikely to cause direct engine damage. However, if left unaddressed, it can lead to other issues that may eventually affect the engine’s performance.

See also  What to Do After Replacing Camshaft Sensor: A Comprehensive Guide

2. Can I drive my vehicle with a bad MDS solenoid?

While it’s technically possible to drive with a bad MDS solenoid, it’s not advisable. A malfunctioning solenoid can lead to decreased fuel efficiency, engine misfires, and rough idling, negatively impacting your driving experience.

3. Can I clean a faulty MDS solenoid instead of replacing it?

In some cases, cleaning the solenoid may resolve minor issues caused by debris or oil buildup. However, if the solenoid is damaged or has internal electrical faults, cleaning alone will not solve the problem.

4. How much does it cost to replace an MDS solenoid?

The cost of replacing an MDS solenoid can vary depending on the vehicle make and model, as well as the labor rates of the repair shop. On average, the cost can range from $200 to $500, including parts and labor.

5. Can I replace the MDS solenoid myself?

If you have sufficient automotive knowledge and the necessary tools, you can attempt to replace the MDS solenoid yourself. However, it’s crucial to consult the vehicle’s service manual and follow the manufacturer’s instructions to ensure a proper installation. If you’re unsure, it’s best to seek professional assistance.

en_USEnglish (United States)
Scroll to Top