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mercedes bad throttle position sensor

Mercedes Throttle Possition Sensor Problem

Mercedes-Benz throttle body or throttle position sensor found on C-Class, E-Class, S-Class, CLK-Class, SLK-Class may fail causing idle issues, no idle or poor acceleration.

Symptoms of defective Mercedes throttle body or throttle position sensor include:

  • Rough idle
  • Mercedes won’t idle
  • High idle
  • Idle at 2000 RPM
  • Sudden idle surges
  • Check engine light on
  • Poor fuel economy
  • Limp Mode
  • Poor Acceleration
  • Fault Code such as P0221, P0120, P012x

A common problem that you may notice is that the car drives fine under normal acceleration. If you press the gas pedal to the floor or try to accelerate quickly or floor it, the engine stops responding, RPMs drop and it may even go into limp mode. Turn off the engine and restarting it usually fix the problem. In ost cases, the issue is caused by either a defective  pedal position sensor or a bad throttle position sensor.

Mercedes Throttle Body

The throttle body is where the throttle valve is mounted and is what control the amount of air that enters the combustion chamber. When there are throttle body malfunctions the wrong amount of air enters into the engine causing problems with air/fuel mixture ratio.

Here is a close up picture of a Mercedes throttle body.

mercedes bad throttle position sensor

Mercedes throttle bodies made by Bosch and VDO may fail. Luckily these units are repairable. Check out these companies that offer Mercedes throttle body repair service (eBay link).

Mercedes Throttle Position Sensor

Another weak point is the throttle position sensor. On models such as E-Class W210 and W208, the Throttle Position Sensor is mounted near the front left strut, on the front of the brake fluid reservoir. Replacing it takes less than 10 min and doesn’t require any special tools other than a 10mm socket and a screwdriver.

mercedes throttle position switch locationMercedes-Benz utilizes a drive-by-wire system. A faulty gas pedal (also known as travel sensor, gas accelerator, pedal position sensor) may develop similar symptoms as a bad throttle position sensor.

Common Causes

  • Defective Throttle Position Sensor (TPS)
  • Dirt build up in throttle body
  • Wiring Harness

How to fix it

First, try throttle reset procedure

  1. Turn the key to ON position. Position II that is. Don’t start the car.
  2. Press and hold the gas pedal for at least five seconds. Keep the pedal pressed.
  3. Turn ignition off but do not remove the key. Now release the gas pedal.
  4. Remove key. Wait a minute before you restart your Mercedes.

This allows resetting the High and Low points of the gas pedal. It also resets the transmission shift points to factory settings. Don’t worry you can’t cause any damage with this reset.

Hopefully, this fixed your problem. If not you need to diagnose throttle position sensor, throttle body. For this, you will need an advanced Mercedes scanner. 

Watch this very informative video on the function of throttle position sensor. Excuse the sense of humor.

If you determine the throttle position sensor has failed on your Mercedes-Benz you will need to address this problem right away. In most cases, you will get code P0120 or P012x. Your options are to replace it with a new throttle position sensor. Mercedes-Benz dealerships would be happy to help you or any Indepdement mechanic. Or you can replace the throttle position sensor yourself to save money.

Check Price: Mercedes Throttle Position Sensor

If your throttle body is defective, you may not be able to repair it yourself. An alternative solution is to use a third party that will refurbish your throttle body. You will need to remove the throttle body from your engine and ship it out to companies that repair these units. There are companies such as BBA Reman that will test and repair your existing unit. These units end up being as good as new and in some cases, these companies provide a lifetime warranty for the part they repair.

List of companies that offer Mercedes Throttle Body Repair (eBay link).

In older cars, when you pressed the gas pedal a cable was connected directly to the throttle valve which opened and closed the throttle valve. Since 2000 Mercedes has been using drive by wire system. Which means you press the gas pedal but there is no cable connected directly to the throttle valve. Instead, there is a potentiometer that detects the position of the gas pedal. This signal is sent to the Engine Control Unit which analyzes the pedal position and several other sensor inputs which then sends the signal to the throttle body to open and close the throttle valve.


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