Why Cruise control and Speedtronic are inoperative.

Cruise control is a feature that allows you to take your feet off the gas pedal while the car takes over acceleration. With the driver only handling the steering wheel and maybe the audio system, long-distance drivers can rest their feet.

In advanced systems (adaptive cruise control) the car maintains a set speed and adjusts the acceleration to keep a safe distance between itself and the car in front. Ordinary systems (conventional cruise control) require you to handle things when the car ahead of you slows down. You can override the adaptive cruise control by pressing the throttle down hard.

So, What Can Cause Problems With Cruise Control And Speedtronic?

This problem mainly affects Mercedes-Benz C300 W204 although other car types and makes can be victims if they use the system. Any inoperative cruise control and speedtronic can be attributed to.

  • The brake switches could be defective
  • The battery might be dead or low
  • The ABS wheel speed sensor might be damaged
  • A blown fuse

Reasons The Cruise Control And Speedtronic Are Inoperative

ABS Sensor Malfunction

Because ABS sensors are installed at each wheel, if one or all of these delicate pieces get damaged, the cruise control will malfunction. Other parts that might get affected include the ESP and the stability control system. The ABS sensor might need replacement to get back on track.

The Battery Is Dead Or Low

A low power supply is enough to trigger the cruise control inoperative warning. The battery might be too old or defective, either way, the cruise control cannot run on insufficient power. To fix the problem you will need to replace the battery.

The Steering Angle Sensor Might Have Issues

This small device behind the steering wheel can trigger the ABS light to come on. As stated above a problem with the ABS is a problem for the cruise control. You can replace the sensors but there is a simple solution to consider before calling the mechanic.

While in parking with the engine running, turn the steering to left and right ends. This should calibrate the steering sensors and handle the cruise control problem.

The Brake Lights Switch Could Be Malfunctioning

It might seem odd but the brake lights can cause the cruise control to fail. The cruise control is made to disengage if the brakes are pressed. If the brake lights are malfunctioning, the cruise control might think the brakes have been engaged and disengage on their own.

To fix it you will need to scan the car since a simple look at the lights will not divulge much.

The Engine Could Have A Misfire

When the engine has a problem the check engine light will come on. The light will trigger the car to go into limp mode. It can be caused by something as small as a cylinder misfire. The ECU will bar the driver from accessing cruise control to protect the car from further engine damage.

The solution to this problem cannot be directly stated because engine problems are subjective. The cruise control will be back on track after the engine problem is identified and rectified.

Issues With The Ground Connection

If the car has been to a flooded or muddy area, water or mud might have messed up connections down there. Some of these connections directly or indirectly affect the cruise control system.

A mechanic will have to run some tests to establish the altered areas.

The MAF Sensor Could Be Damaged

A problem with the Mass airflow sensor could cause the check engine and inoperative cruise control lights to come on. Fix the MAF sensors and test for improvement.

A Bad Fuse

Almost every electronically controlled system has a fuse to protect it from short circuits. The cruise control has one and if it blows up, the system will respond by going off.

To fix this issue you might have to replace the fuse.

The Actuator Might Be Damaged

If you are driving an older car, you should know that cruise control is maintained using a vacuum actuator. There are some hoses and cables around the actuator too. If any of these parts get damaged or stop working, the cruise control will fail.

To fix it you can get a new actuator or replace the damaged fuses.

Can I Drive With A Bad Cruise Control And Speedtronic?

If you are used to driving with cruise control and speedtronic engaged a slight problem with either will be annoying. Yes, the car will move if the cause of the cruise control inoperative warning cannot stop it.

The reasons behind cruise control failure are many with some serious and others minor. If the cause of the problem is not serious enough to make the engine inoperative then the car can drive.

You are however not advised to engage the cruise control if it has issues. A situation where the cruise control fails on the fast lane could be disastrous for the driver and other road users

Can Cruise Control And Speedtronic Be Fixed?

Yes, before driving to the repair shop there is a short procedure you can follow to fix the problem.

  • Stop and park in a safe area
  • Shut the engine off
  • Let it rest for 5-10 minutes
  • Restart and check to see if the cruise control is back on track
  • Check to see if you have a blown fuse, you can just replace it.
  • If the problem persists then further troubleshooting and scanning is required. Call your mechanic or drive to your repair shop.

How Much Does It Cost To Fix?

There is no perfect answer to this problem because there are multiple causes of cruise control failure whose repair costs vary. The cost to replace a cruise control or brake switch is anywhere around $130-$400. If the problem lies in the actuator you might spend up to $750.

Final Thoughts

Long-distance drivers love the cruise control and speedtronic features; they allow them to rest their feet during long drives. The system sometimes fails and it is often hard to get it fixed by yourself, so you should get to an authorized repair shop for further investigations and possible solutions.

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