Mercedes-Benz 420SEL Cruise Control Isn't Working

Common Causes of Cruise Control Malfunctions in Your Mercedes-Benz 420SEL and How to Fix Them

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Reviewed by
Bo Fader
Written by RepairPal Car Genius
Updated January 14, 2025
0%
30% chance it's the
Sensor
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25% chance it's the
Control Module
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25% chance it's the
Throttle
0%
20% chance it's
Something else
The most common reasons a Mercedes-Benz 420SEL cruise control isn't working are failed control module, sensor or switch issues, or throttle actuation problems.
  • Sensor: A faulty or malfunctioning sensor can lead to incorrect readings, causing issues with engine performance or other systems relying on accurate data.
  • Control Module: A faulty control module can lead to erratic vehicle behavior or failure of various electronic systems due to improper signal processing.
  • Throttle: A faulty throttle body or a defective accelerator pedal position sensor may be causing inconsistent throttle response.
Proper diagnosis will determine the exact cause of your symptom, saving you money on unnecessary repairs. The diagnostic experts at RepairPal Certified shops have the right tools and experience to solve any symptom.

How much does it cost to fix a Mercedes-Benz 420SEL cruise control isn't working?

Common Repairs

The total repair cost will vary based on the condition of your vehicle and the number of repairs needed to fix your symptom. Proper diagnosis will save you money by finding the exact repairs needed to fix your car right the first time.

When the throttle position sensor fails, the engine's computer tends to overcompensate with fuel, leading black exhaust coming from the tailpipe. There is a strong possibility of engine misfires, and the check engine light will come on.

Throttle position sensors can also develop "dead spots," or certain places along the throttle curve where it doesn't get a reading. When this happens, the above symptoms can occur but then stop when you further press or let off the gas pedal.

In the event that a wheel speed sensor fails, the ABS, traction control system (TCS) and manufacturer specific stability control system lights will illuminate, informing the driver that the systems are disabled. The vehicle will be more prone to tire slip, and normal driving patterns may need to be adjusted to correct for the loss of computer control. On older vehicle's, the speedometer can be affected, causing illumination of the check engine light as well.

Troubleshooting Cruise Control Issues in a Mercedes-Benz 420SEL

When troubleshooting cruise control issues in a Mercedes-Benz 420SEL, it's crucial to follow a structured diagnostic approach that begins with the simplest potential problems. Start by examining the brake light switch, as a faulty switch can prevent the cruise control from functioning properly, even if the brake lights seem to work. Next, inspect the electrical connections and fuses to ensure they are intact and secure, as poor connections can lead to various malfunctions. If these checks do not yield results, turn your attention to the throttle control system, since any irregularities here can significantly impact cruise control performance. Additionally, assess the ABS sensors, as their malfunction can disable the cruise control along with other essential systems. For older models, don't overlook the vacuum lines; any damage or leaks in these lines can also cause cruise control failure. By methodically addressing these areas, you can effectively diagnose and resolve the cruise control issues in your Mercedes-Benz 420SEL.

What Are the Common Problems Causing Cruise Control Issues in a Mercedes-Benz 420SEL?

When dealing with cruise control issues in a Mercedes-Benz 420SEL, it's essential to understand the common problems that may arise. A failed control module, sensor, or switch can disrupt the entire system, leading to malfunction. Additionally, throttle actuation problems can prevent the cruise control from engaging properly. It's also important to consider the ABS sensor; a failure in any wheel's ABS sensor can disable not only the cruise control but also other critical systems like ABS and stability control. Electrical issues, such as poor fuse connections, can further complicate matters, causing intermittent or complete failures. The cruise control amplifier is another component that may fail, often showing classic symptoms that indicate a need for replacement. Moreover, a malfunctioning brake pedal switch can abruptly stop the cruise control from functioning, as it is designed to disengage the system when the brakes are applied. Lastly, worn-out or damaged components, particularly the control switch, can lead to operational failures. By understanding these potential issues, DIYers can better diagnose and address cruise control problems in their Mercedes-Benz 420SEL, ensuring a smoother driving experience.

Why is the Cruise Control Not Working in a Mercedes-Benz 420SEL?

When the cruise control in your Mercedes-Benz 420SEL is malfunctioning, it’s crucial to address the issue without delay. Ignoring symptoms such as a non-responsive system can lead to more significant problems, including potential safety hazards while driving. A defective brake pedal switch, for instance, not only prevents the cruise control from engaging but can also affect your ability to control the vehicle effectively. Additionally, if the ABS wheel speed sensor is faulty, it may trigger warning lights that indicate deeper issues within the braking system, which could compromise your safety on the road. Furthermore, problems with the throttle control system or blown fuses can lead to erratic vehicle behavior, making it essential to investigate these issues promptly. By diagnosing and resolving these problems early, you not only enhance your driving experience but also prevent costly repairs down the line. Therefore, if you notice any signs of cruise control failure, consider a thorough inspection to ensure your vehicle remains safe and reliable.

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