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Mercedes-Benz E-Class: How to Replace Ignition Coils

Ignition coils transfer electrical power from the battery to the spark plugs. They are computer controlled to release the spark at the ideal time in the combustion process. As wear occurs over time, the coils lose their ability to transfer enough electrical power, causing poor throttle response and misfires.

By Weston Chadwick - June 15, 2015
Contributors: Dexion

This article applies to the Mercedes-Benz E-Class (2002-2009).

The ignition coils contain a transistor that has three paths for current flow. One section is called the base. Connected to the base is an emitter. The emitter receives a small amount of voltage when it's time for the spark plugs to fire, and allows current to flow through the base (like an open door). The door closes again once the voltage is removed from the emitter. The ignition coil also contains a permanent magnet inside wrapped by two different sized sections of wires. These are called the primary and secondary windings. When current is introduced into the primary windings, the voltage increases dramatically to about 10,000 volts as it transfers into the secondary windings by way of magnetism. This high voltage is then sent to the spark plug.

Over time, these windings can build corrosion and the magnet can crack due to road vibrations. Once the available voltage is lower than the required voltage, a spark will not occur at the spark plug, thus causing a misfire and hesitation.

Materials Needed

  • Mercedes-Benz spark plug boot puller
  • 5/8" spark plug socket 3/8" drive
  • 3" extension 3/8" drive
  • 3/8' ratchet
  • T27 Torx socket/folding Torx set

Step 1 – Remove the air intake tubes, engine cover, and air box

There are two air intake tubes coming from each side of the air box. These simply slide off the air box and the shroud near the front bumper.

The engine cover is a two piece design. It wraps around the oil cap and is removed by pulling the front edge up, then pulling the entire cover forward with a slight twist to pop the locking tabs free.

The air box is held in place by four tabs. Two are at the front and two are at the rear. Pulling up on the two front tabs will release all four.

  • Figure 1. Removing the engine cover.
  • Figure 2. Removing the air box and intake hoses. Pull the intake hoses in the direction of the arrow to remove them from the air box.

Step 2 – Remove the coil packs

You will now have access to the coil packs. Remove the connectors from the coil packs by squeezing the clip and pulling them at the same time. Then use your Torx bit to remove the T27 Torx bolt. Lastly, you will use the Mercedes spark plug boot removal tool (17mm offset wrench) and pull the boots off with a careful prying motion.

  • Figure 3. The coil packs.
  • Figure 4. Disconnect the connector by squezzing the tab in the direction of the arrow.

Step 3 – Remove the spark plug wires

Remove the spark plug wires off the old coil packs. Keep the wires in order as you are removing and installing them onto the new coil packs. If any are different lengths, this will ensure they reach the spark plugs and are routed correctly. The spark plug wires pull straight off the coil packs.

Figure 5. The coil packs removed from the vehicle.

Step 4 – Re-install the coil packs

  • Place the coil packs back into position and thread the T27 Torx bolt into place.
  • Push the spark plug boots back onto the spark plugs. You will hear a slight pop sound when the boot is fully engaged to the plug.
  • Re-connect the connectors. You will hear the tabs lock into place.
  • You can use a torque wrench to tighten down the coil packs, but it's not required. The T27 Torx bolt is only torqued to about 5 ft lb.
  • Finally re-install the air box, engine cover, and intake tubes.

Featured Video: How to Replace Spark Plugs and Wires

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