P0718 Code Mercedes: Diagnosis, Causes, and Solutions

1. Understanding the P0718 Code Mercedes

The P0718 code on a Mercedes-Benz signifies an intermittent fault within the input/turbine speed sensor “A” circuit. The Powertrain Control Module (PCM) uses data from this sensor to monitor transmission performance. When the PCM detects a signal from this sensor that falls outside the expected range, even sporadically, it triggers the P0718 code. This code is prevalent in vehicles using OBD-II systems. The input speed sensor, found near the bell housing by the transmission input shaft, works with a notched reluctor wheel. A deviation in the input/turbine speed can bring about issues in the system.

2. Decoding the Technical Details of P0718

The P0718 code is not just a simple error message; it points to a very specific type of problem. The input/turbine speed sensor is critical for the proper functioning of the automatic transmission, especially in Mercedes-Benz vehicles. Here’s a breakdown of what’s happening:

• Sensor Function: The sensor measures the rotational speed of the transmission’s input shaft. This information is used by the PCM to control shift timing, torque converter lockup, and other vital transmission functions.
• Intermittent Nature: The “intermittent” descriptor in the code means the problem isn’t constant. It appears and disappears, making diagnosis more challenging.
• Circuit “A”: This specifies which of potentially multiple input speed sensors is experiencing the problem.
• OBD-II System: This is the standardized diagnostic system used in most modern vehicles, allowing for the retrieval of trouble codes.

Why is this sensor important? Without accurate input speed data, the transmission can’t operate efficiently or reliably. The PCM relies on this information to make real-time adjustments to ensure smooth and optimal performance.
Mercedes Transmission Speed Sensor

3. Identifying the Symptoms of P0718 in Your Mercedes

Recognizing the symptoms associated with the P0718 code is essential for timely diagnosis and repair. While the specific symptoms may vary slightly depending on the Mercedes-Benz model, here are some common indicators:

• Erratic Speedometer Operation: The speedometer may fluctuate, show inaccurate readings, or even fail completely.
• Improper Shifting: The transmission may shift harshly, erratically, or at the wrong times. You might notice delayed shifts, slipping, or failure to shift altogether.
• Speedometer and/or Odometer Failure: In some cases, the speedometer and odometer may stop working entirely.
• Erratic or Harsh Transmission Shift Points: The transmission might shift abruptly or at inconsistent points.
• Decreased Fuel Efficiency: The engine may consume more fuel than usual due to inefficient transmission operation.
• Check Engine Light: The check engine light will illuminate on the dashboard.
• Transmission Slipping: Experiencing a lack of power or delayed response when accelerating.

Severity of Symptoms: The severity of these symptoms can vary. In some cases, the problem might be subtle, with only occasional shifting issues. In other cases, the transmission may become almost undriveable.

4. Root Causes of the P0718 Code in Mercedes Vehicles

Understanding the potential causes of the P0718 code is crucial for effective troubleshooting. Here’s a detailed breakdown of the most common culprits in Mercedes-Benz vehicles:

• Defective Input Speed Sensor: The sensor itself may be faulty due to wear and tear, internal damage, or manufacturing defects.
• Damaged Wiring or Connectors: Wires can become frayed, corroded, or broken, while connectors can loosen or become damaged, leading to poor electrical connections.
• Faulty Powertrain Control Module (PCM): Although less common, the PCM itself could be the source of the problem. Internal PCM failures can lead to incorrect signal processing.
• Programming Error in the PCM: In rare cases, the PCM might have a software glitch or require reprogramming.
• Metal Debris on the Magnetic Sensor: Metal shavings or debris can accumulate on the sensor, interfering with its ability to read the speed accurately.
• Transmission Problems: Internal mechanical issues within the transmission can sometimes affect the input speed sensor readings.

Troubleshooting Tip: Start with the most accessible and common causes first. Check the wiring and connectors before assuming the sensor is faulty.
Damaged Car Wiring

5. Step-by-Step Diagnostic Procedures for P0718 on Mercedes

Diagnosing the P0718 code on a Mercedes-Benz requires a systematic approach. Here’s a step-by-step procedure to guide you through the process:

1. Read the Code: Use an OBD-II scanner to confirm the presence of the P0718 code. Note any other related codes that may be present.

2. Visual Inspection: Carefully inspect the wiring and connectors leading to the input speed sensor. Look for any signs of damage, corrosion, or loose connections.

3. Sensor Testing: Use a multimeter to test the sensor’s resistance and voltage output. Compare your readings to the manufacturer’s specifications.

   • Resistance Test: Disconnect the sensor and measure the resistance between its terminals.
   • Voltage Test: With the key on and the engine off, check for the presence of voltage at the sensor connector.

4. Wiring Harness Testing: Use a multimeter to check for continuity and shorts in the wiring harness.

   • Continuity Test: Ensure there are no breaks in the wires.
   • Short to Ground Test: Check for any wires that are shorting to ground.

5. PCM Inspection: Visually inspect the PCM for any signs of damage, such as corrosion or burnt components.

6. Data Stream Analysis: Use a scan tool to monitor the input speed sensor data in real-time while driving the vehicle. Look for any dropouts or inconsistencies in the signal.

Tools Needed:

• OBD-II Scanner
• Multimeter
• Wiring Diagram (specific to your Mercedes-Benz model)
• Basic Hand Tools

Safety Precautions: Always disconnect the battery before working on electrical components.

6. Repair Strategies to Resolve the P0718 Code

Once you’ve identified the cause of the P0718 code, you can proceed with the necessary repairs. Here are some common repair strategies:

• Replace the Input Speed Sensor: If the sensor is faulty, replacing it is the most straightforward solution.
• Repair or Replace Damaged Wiring/Connectors: Repair any damaged wires or replace faulty connectors. Ensure all connections are clean and secure.
• PCM Replacement/Reprogramming: If the PCM is faulty, it may need to be replaced or reprogrammed. This is typically done by a qualified technician.
• Clean Metal Debris: If metal debris is present on the sensor, carefully clean it off. You may also want to inspect the transmission for any signs of internal damage.
• Check Transmission Fluid: Ensure it is at the correct level and is free of debris.
• Address Internal Transmission Issues: If the P0718 code is caused by internal transmission problems, more extensive repairs may be necessary.

Important Note: Always use high-quality replacement parts that are specifically designed for your Mercedes-Benz model.

7. Preventative Measures to Avoid Future P0718 Issues

While you can’t completely eliminate the risk of the P0718 code occurring, there are some preventative measures you can take to minimize the chances:

• Regular Transmission Service: Follow the manufacturer’s recommended transmission service schedule, including fluid changes and filter replacements.
• Careful Driving Habits: Avoid harsh acceleration and sudden stops, which can put unnecessary stress on the transmission.
• Address Minor Issues Promptly: If you notice any unusual symptoms, such as rough shifting, have them checked out by a qualified technician as soon as possible.
• Protect Wiring: Protect exposed wiring from damage by using wire looms or other protective coverings.
• Use Quality Parts: When replacing any transmission components, use high-quality parts from reputable manufacturers.
• Routine Inspections: Regularly inspect the wiring and connectors around the transmission for any signs of damage or corrosion.

8. How CARDIAGTECH.NET Can Help with Your Mercedes Repair

At CARDIAGTECH.NET, we understand the complexities of diagnosing and repairing modern vehicles, especially Mercedes-Benz models. We offer a wide range of diagnostic tools and equipment to help you tackle the P0718 code and other automotive issues.

Our Products and Services Include:

• OBD-II Scanners: High-quality scanners that can read and clear diagnostic trouble codes.
• Diagnostic Software: Advanced software for in-depth analysis of vehicle systems.
• Wiring Diagrams: Comprehensive wiring diagrams specific to Mercedes-Benz models.
• Technical Support: Expert technical support to help you troubleshoot complex problems.
• Training Resources: Access to training materials and resources to enhance your diagnostic skills.

Why Choose CARDIAGTECH.NET?

• Expertise: We have years of experience in the automotive diagnostic industry.
• Quality Products: We offer only the highest quality tools and equipment.
• Customer Support: We’re committed to providing exceptional customer support.
• Competitive Pricing: We offer competitive prices on all our products and services.

Contact CARDIAGTECH.NET today at 276 Reock St, City of Orange, NJ 07050, United States or Whatsapp: +1 (641) 206-8880 to learn more about how we can help you with your Mercedes-Benz repair needs. Visit our website at CARDIAGTECH.NET for more information.

9. Understanding Mercedes-Benz Transmission Systems

To effectively address the P0718 code, it’s beneficial to have a basic understanding of how Mercedes-Benz transmissions work. These transmissions are complex systems with numerous sensors and actuators that work together to provide smooth and efficient gear changes.

Key Components:

• Input Speed Sensor: Measures the rotational speed of the transmission’s input shaft.
• Output Speed Sensor: Measures the rotational speed of the transmission’s output shaft.
• Transmission Control Module (TCM): Controls the shifting process based on data from various sensors.
• Solenoids: Electrically operated valves that control the flow of transmission fluid to different parts of the transmission.
• Torque Converter: A fluid coupling that transfers power from the engine to the transmission.

How It Works:

The TCM uses data from the input and output speed sensors, along with other sensors, to determine the appropriate gear for the current driving conditions. It then activates the appropriate solenoids to engage the correct gears. The torque converter provides smooth power transfer and helps to dampen vibrations.

Mercedes-Benz Specifics:

Mercedes-Benz transmissions are known for their smooth shifting and advanced features. However, they can also be more complex and require specialized diagnostic tools and knowledge.

10. Tools and Equipment for Diagnosing P0718 Code Mercedes

Having the right tools and equipment is essential for accurately diagnosing the P0718 code on a Mercedes-Benz. Here’s a list of essential tools:

• OBD-II Scanner: A must-have tool for reading and clearing diagnostic trouble codes.
• Multimeter: Used to test the resistance, voltage, and continuity of electrical circuits.
• Wiring Diagram: A detailed diagram of the vehicle’s electrical system.
• Scan Tool: A more advanced tool that can access real-time data and perform diagnostic tests.
• Hand Tools: Basic hand tools such as wrenches, sockets, and screwdrivers.
• Torque Wrench: Used to tighten bolts to the correct torque specifications.
• Hydraulic Jack and Jack Stands: Used to safely lift the vehicle for inspection and repair.

Choosing the Right Tools:

When choosing diagnostic tools, it’s important to select high-quality tools from reputable manufacturers. Look for tools that are specifically designed for Mercedes-Benz vehicles.

Alt: Car diagnostic tools used in assessing P0718 error.

11. Understanding the Role of the PCM in the P0718 Error

The Powertrain Control Module (PCM) is the brain of the engine and transmission control systems. It receives data from various sensors, including the input speed sensor, and uses this information to control various functions, such as fuel injection, ignition timing, and gear shifting.

PCM Functions Related to P0718:

• Monitoring Input Speed Sensor Data: The PCM continuously monitors the data from the input speed sensor.
• Calculating Shift Points: The PCM uses input speed data to determine the optimal shift points for the transmission.
• Controlling Solenoids: The PCM controls the solenoids that engage the different gears in the transmission.
• Detecting Faults: The PCM detects any faults in the input speed sensor circuit and sets the P0718 code.

PCM Failure:

While less common, a faulty PCM can cause the P0718 code. If the PCM is not processing the input speed sensor data correctly, it may trigger the code even if the sensor itself is functioning properly.

12. Step-by-Step Guide to Replacing the Input Speed Sensor

If you’ve determined that the input speed sensor is faulty, here’s a step-by-step guide to replacing it:

1. Gather Tools and Supplies: You’ll need a new input speed sensor, a socket set, a wrench, a screwdriver, and a torque wrench.
2. Disconnect the Battery: Disconnect the negative battery terminal to prevent electrical shock.
3. Locate the Input Speed Sensor: The input speed sensor is typically located on the side of the transmission case, near the input shaft. Consult a repair manual for the exact location on your Mercedes-Benz model.
4. Disconnect the Connector: Disconnect the electrical connector from the sensor.
5. Remove the Sensor: Use a socket or wrench to remove the sensor from the transmission case.
6. Install the New Sensor: Install the new sensor, being careful not to overtighten it.
7. Reconnect the Connector: Reconnect the electrical connector to the sensor.
8. Reconnect the Battery: Reconnect the negative battery terminal.
9. Clear the Code: Use an OBD-II scanner to clear the P0718 code.
10. Test Drive: Take the vehicle for a test drive to ensure that the problem is resolved.

Important Tips:

• Always use a new input speed sensor from a reputable manufacturer.
• Be careful not to damage the transmission case when removing or installing the sensor.
• Tighten the sensor to the correct torque specification.

13. Inspecting and Repairing Wiring and Connectors

Damaged wiring and connectors are a common cause of the P0718 code. Here’s how to inspect and repair them:

1. Visual Inspection: Carefully inspect the wiring and connectors for any signs of damage, such as frayed wires, cracked insulation, or corroded terminals.
2. Continuity Test: Use a multimeter to test the continuity of the wires.
3. Voltage Test: Check for the presence of voltage at the connector.
4. Repairing Wires: If you find any damaged wires, repair them using crimp connectors or solder.
5. Replacing Connectors: If a connector is damaged, replace it with a new one.

Tips for Wiring and Connector Repair:

• Use high-quality crimp connectors or solder.
• Protect repaired wires with heat shrink tubing.
• Ensure all connections are clean and secure.

14. Resetting the PCM After Repairs

After making repairs, it’s important to reset the PCM to clear the P0718 code and allow the system to relearn. Here’s how to do it:

• Using an OBD-II Scanner: The easiest way to reset the PCM is to use an OBD-II scanner. Simply connect the scanner to the vehicle and follow the instructions to clear the codes.
• Disconnecting the Battery: You can also reset the PCM by disconnecting the negative battery terminal for 15-20 minutes. This will erase the PCM’s memory.

Important Note: After resetting the PCM, the vehicle may exhibit some unusual driving characteristics for the first few miles as the system relearns.

15. Common Mistakes to Avoid When Addressing the P0718 Code

When addressing the P0718 code, it’s important to avoid these common mistakes:

• Ignoring Symptoms: Don’t ignore any symptoms, even if they seem minor.
• Assuming the Sensor is Always the Problem: Always perform a thorough diagnosis before replacing the sensor.
• Using Cheap Parts: Use high-quality replacement parts from reputable manufacturers.
• Skipping the Wiring Inspection: Always inspect the wiring and connectors for damage.
• Not Resetting the PCM: Always reset the PCM after making repairs.
• Neglecting Transmission Service: Follow the manufacturer’s recommended transmission service schedule.

16. Advanced Diagnostic Techniques for P0718

If you’ve tried the basic diagnostic steps and are still unable to resolve the P0718 code, you may need to use some advanced diagnostic techniques:

• Using a Scan Tool: A scan tool can provide real-time data and perform diagnostic tests.
• Performing a Transmission Fluid Analysis: Analyzing the transmission fluid can provide valuable information about the condition of the transmission.
• Using an Oscilloscope: An oscilloscope can be used to analyze the input speed sensor signal.

When to Seek Professional Help:

If you’re not comfortable performing these advanced diagnostic techniques, it’s best to seek professional help from a qualified technician.

17. The Importance of Regular Maintenance for Mercedes Transmissions

Regular maintenance is crucial for keeping your Mercedes-Benz transmission in good condition and preventing problems like the P0718 code. Here are some key maintenance tasks:

• Fluid Changes: Change the transmission fluid at the intervals recommended by the manufacturer.
• Filter Replacement: Replace the transmission filter at the same time as the fluid change.
• Inspection: Inspect the transmission for leaks and damage.
• Adjustment: Adjust the transmission bands and linkages as needed.

Benefits of Regular Maintenance:

• Prolonged Transmission Life: Regular maintenance can help to prolong the life of your transmission.
• Improved Performance: A well-maintained transmission will perform better.
• Reduced Repair Costs: Regular maintenance can help to prevent costly repairs.

18. Understanding Diagnostic Trouble Codes (DTCs) in Mercedes

The P0718 code is just one of many Diagnostic Trouble Codes (DTCs) that can be triggered in a Mercedes-Benz vehicle. Understanding how DTCs work is essential for effective troubleshooting.

• What are DTCs? DTCs are codes that are stored in the vehicle’s computer when a fault is detected in one of the systems.
• How are DTCs Read? DTCs are read using an OBD-II scanner.
• What do DTCs Mean? Each DTC corresponds to a specific fault in the vehicle.

Using DTCs for Troubleshooting:

DTCs can be used to quickly identify the source of a problem. However, it’s important to remember that a DTC is just a starting point. You’ll need to perform further diagnosis to determine the exact cause of the problem.

19. The Role of Transmission Fluid in Preventing P0718 Code Mercedes

The transmission fluid plays a vital role in the operation and longevity of your Mercedes-Benz transmission. It lubricates moving parts, cools the transmission, and helps to transmit power.

Why is Transmission Fluid Important?

• Lubrication: Transmission fluid lubricates the gears, bearings, and other moving parts in the transmission, reducing friction and wear.
• Cooling: Transmission fluid helps to cool the transmission by carrying heat away from the moving parts.
• Power Transmission: Transmission fluid helps to transmit power from the engine to the transmission.

Maintaining Transmission Fluid:

• Check the Fluid Level: Check the transmission fluid level regularly.
• Change the Fluid: Change the transmission fluid at the intervals recommended by the manufacturer.
• Use the Correct Fluid: Use the correct type of transmission fluid for your Mercedes-Benz model.

20. Case Studies: Real-World Examples of P0718 Diagnosis and Repair

To illustrate the diagnostic and repair process, here are a few real-world case studies involving the P0718 code in Mercedes-Benz vehicles:

Case Study 1:

• Vehicle: 2012 Mercedes-Benz C-Class
• Symptoms: Erratic shifting, check engine light
• DTC: P0718
• Diagnosis: Faulty input speed sensor
• Repair: Replaced the input speed sensor

Case Study 2:

• Vehicle: 2015 Mercedes-Benz E-Class
• Symptoms: Harsh shifting, decreased fuel efficiency
• DTC: P0718
• Diagnosis: Damaged wiring to the input speed sensor
• Repair: Repaired the damaged wiring

Case Study 3:

• Vehicle: 2018 Mercedes-Benz S-Class
• Symptoms: Transmission slipping, check engine light
• DTC: P0718
• Diagnosis: Faulty PCM
• Repair: Replaced the PCM

These case studies highlight the importance of a thorough diagnosis to accurately identify the cause of the P0718 code.

FAQ: Addressing Your Concerns About P0718 Code Mercedes

1. What exactly does the P0718 code mean for my Mercedes?

The P0718 code signals an intermittent issue with the input/turbine speed sensor circuit. This sensor helps your car’s computer manage transmission performance, and the “intermittent” part means the problem comes and goes, making it tricky to diagnose.

2. Can I drive my Mercedes with the P0718 code active?

It’s generally not recommended. Driving with the P0718 code can lead to unpredictable shifting and potential damage to your transmission. Get it checked as soon as possible.

3. How much will it cost to fix the P0718 code on my Mercedes?

The cost varies depending on the cause. Replacing a sensor might be a few hundred dollars, while PCM issues could be more expensive. Get a quote from a trusted mechanic.

4. Is the P0718 code a serious problem for my Mercedes?

Yes, it can be. It affects the transmission, which is a critical component. Ignoring it can lead to more extensive and costly damage.

5. Can I fix the P0718 code myself, or do I need a mechanic?

If you have experience with car repairs and diagnostic tools, you might be able to fix it yourself. However, if you’re not comfortable working on your car, it’s best to take it to a mechanic.

6. What are the first steps I should take when the P0718 code appears?

Start by using an OBD-II scanner to confirm the code. Then, visually inspect the wiring and connectors leading to the input speed sensor for any damage.

7. How often should I change my Mercedes’ transmission fluid?

Follow your Mercedes-Benz owner’s manual for recommended transmission fluid change intervals. Regular fluid changes can help prevent transmission problems.

8. Can low transmission fluid cause the P0718 code?

While low fluid itself might not directly cause the P0718 code, it can contribute to transmission issues that indirectly affect the sensor’s performance.

9. Will replacing the input speed sensor always fix the P0718 code?

Not always. The sensor is a common culprit, but the code can also be caused by wiring issues, PCM problems, or even internal transmission issues. A proper diagnosis is essential.

10. Where can I find reliable diagnostic tools and parts for my Mercedes?

CARDIAGTECH.NET offers a wide range of diagnostic tools and high-quality parts specifically designed for Mercedes-Benz vehicles. Contact us at +1 (641) 206-8880 or visit our website for more information.