Mercedes-Benz of Stevens Creek - 2047
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Mercedes-Benz of Stevens Creek - 2047

Mercedes-Benz C 240 Alternator Problems - How To Troubleshoot and Fix

Your Mercedes-Benz C 240 alternator is responsible for charging your car's battery. Located on your engine, alternators spin to generate electricity, which interacts with voltage regulators to provide the correct amount of current to your vehicle. It delivers roughly 13.6 to 14.6 volts while the engine is running.

This battery powers all of your vehicle's electrical components, such as your engine, radio, and warning lights. With heavy wear and tear, alternators can short circuit or cause the bearings to grind. Enough grinding and your serpentine belt may separate from the alternator pulley. If this happens, your car may sputter or refuse to start. Think of your alternator as your battery's charger.


Mercedes-Benz C 240 Bad Alternator Symptoms


Dead Battery

If you turn the ignition key and your engine and dashboard components (AC, radio, etc.) do not start, you probably have a dead battery.

Troubleshooting and fixing a dead battery is very easy to do. Simply locate another vehicle with a working battery and connect a pair of jumper cables from the live vehicle to your vehicle's dead battery. If applied correctly, a few cranks of the ignition switch should bring your engine back to life.


"ALT" Sign on the Dashboard

If your dashboard flashes an "ALT" or "charge" sign, the alternator is not sending power to your battery.


Voltage Leak

Defective alternators have leaky diodes, which are responsible for producing direct current to your battery. Leaking AC voltage causes your vehicle's electrical components to flicker or shut off altogether.


Test Your Alternator

Check for your alternator's voltage by using a digital volt ohmmeter. It only takes a few steps:

  1. Turn your engine off.
  2. Connect your voltmeter's red lead to your battery's positive post and the black lead to the battery's negative post.
  3. Your voltmeter should read 12.65 volts or greater. Anything less and you likely have a dead battery or alternator issues.


How To Replace A Defective Alternator on Your Mercedes-Benz C 240

To replace a defective alternator on your Mercedes-Benz C 240, perform the following steps.

  1. Secure 10mm, 12mm, 13mm, 14mm, and 15mm socket wrenches.
  2. Open your door and locate your main power terminal's dust boot to locate the main power wire, which is connected to your battery.
  3. Remove the nut using a socket or wrench. Grab your main power wire and slide it off your alternator charge terminal.
  4. Wiggle and remove the monitoring wiring harness connector, along with the bracket, upper mounting bolt, and lower mounting bolt.
  5. Pull the alternator out from the engine bay. Be sure to remove loose components safely out of the way (e.g. radiator hose) if it is blocking.
  6. Perform a quick eye check of your old alternator to the new alternator. Ensure identical pulley size, mounting bolt locations, and serpentine belt grooves.
  7. Reinstall your replacement alternator, computer wiring harness, main charge cable, and mounting nut. Be sure to gently knock your press-fit sleeve outward to accommodate your replacement alternator. If done correctly, your lower alternator should seamlessly fit in.
  8. Perform a quick eye check of your accessory pulley belt to make sure they are properly set.
  9. Reconnect your negative battery cable.

While installing, be sure not to damage components nearby, including your radiator core. This is especially true when reinstalling your lower mounting bolt. Be sure to tighten your lower bolt by applying roughly 35 pounds of torque.

All in all, troubleshooting, fixing, and replacing damaged alternators can be done from the safety of your own garage. For any replacement parts, visit the Mercedes-Benz national store. If you are not comfortable troubleshooting and fixing using the above steps, we recommend taking it into your local Mercedes-Benz technician/dealership as the last resort.