A Short Guide On Mercedes Sprinter Glow Plug Fixing

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If your Mercedes-Benz Sprinter is diesel-powered, glow plugs will be used to generate the necessary heat to start the combustion process.

Glow plugs are long metal tubular devices with an internal element that are put into the engine. An electrical connector is attached to the external top section of the glow plug, while the internal bottom section resides inside the engine, above the cylinder.

The glow plug heats up and the tip glows when a diesel engine is started, which is why they are called glow plugs. The glow plug's heat warms the air and fuel in the cylinder, allowing combustion to begin.

The glow plugs will be turned off once the diesel engine has started and warmed up. The length of time the glow plugs stay lit after the engine has started is determined by the glow plugs, the engine, and the ignition system. After 3 to 5 minutes, certain plugs may turn off.

You may need to wait for the glow plug to heat up before starting the engine in colder climates, and some vehicles may be equipped with air intake heaters to raise air temperatures, or you may not notice any delay in starting the diesel.

Glow plugs are long-lasting, but the more you use them, the faster they wear out, become damaged, and fail. A glow plug's life might also be shortened by carbon buildup or engine pollutants. When glow plugs fail, the car may take longer to start or not start at all, or it may misfire, resulting in smoke from the exhaust.

Glow plugs will ultimately need to be replaced due to wear and tear.

Table Of Content

  1. Which events occur when you start a diesel-powered Mercedes-Benz Sprinter
  2. What are the signs that a glow plug control module in Mercedes-Benz Sprinter is faulty?
  3. Problems with glow plugs in Mercedes-Benz Sprinter and how to fix them
  4. How to clean glow plugs in a diesel engine Mercedes Benz Sprinter
  5. How to replace Mercedes-Benz glow plugs: A step-by-step guide
  6. When should your glow plug control module be replaced?
  7. Conclusion

Which Events Occur When You Start A Diesel-Powered Mercedes-Benz Sprinter

Mercedes Benz Sprinter

  • Based on information from the Engine Control Unit, the glow plug control module determines the timing and electric current required by the glow plugs.
  • The glow plug's heating element is electrified, which causes it to heat up and emit visible light (thus the name).
  • The air that enters the system is compressed.
  • The fuel injector spray directs fuel to the glow plug's hot tip.
  • Even when the engine is cold, the injected gasoline mixes with the compressed air evaporates and begins burning practically instantly.
  • The glow plug stays on during the pre-heating phase to ensure proper fuel combustion and minimise your car's environmental effect.

Glow plug

The increase in temperature of the intake air during compression, as well as the relatively low ignition temperature of diesel, aid this process. However, a glow plug control module is still required since, without it, the compression temperature of a cold diesel engine may not be high enough to assure effective ignition of the injected fuel. As a result, exhaust emissions would rise.

What Are The Signs That A Glow Plug Control Module In Mercedes-Benz Sprinter Is Faulty?

Glow plug connection diagram

The glow plugs in a diesel engine are controlled by a single glow plug control module. This implies that if a single glow plug fails, you may not notice because it only affects one cylinder in your engine. However, if two of the three fail or the control module itself fails, starting the engine will become increasingly difficult. Here are some frequent indications of a malfunctioning glow plug or glow plug control module, in addition to looking for the glow plug light on your dashboard:

White Smoke Emanates From Exhaust

Diesel will seep into the exhaust system and burn due to a faulty glow plug.

Glow plug location

Engine Becomes Difficult To Start

This could indicate that the engine starts slowly in hot weather or does not start at all in cold weather. This, however, could be a sign of a problem with the fuel system or the batteries.

Engine Power Is Insufficient

Due to inefficient combustion, which affects power and efficiency, defective glow plugs will make it difficult for your automobile to function effectively after a tough start.

Glow plug module

Problems With Glow Plugs In Mercedes-Benz Sprinter And How To Fix Them

In a diesel engine, glow plugs pre-heat the injection chamber, making it easier to start. The pre-heat cycle of the glow plug system is controlled by the glow plug relay, which is based on the reading from the cylinder head's temperature sensor. If your Mercedes-Benz Sprinter is running rough and has no pick-up, or if black smoke is spewing out the back, check for glow plug problems.

1st Step

Determine which sections of the glow plug system are simple to reach. Begin with the easiest and work your way up to the most difficult. This procedure will assist in determining the logical sequence in which the various components of the glow plug system should be tested.

Mercedes sprinter hood

2nd Step

Locate the glow plug temperature relay's wire. Reconnect the wire if it's been disconnected.

3rd Step

Connect a test light to the glow plugs to see if they are getting the power they need. The plug is receiving electricity if the test light illuminates.

4th Step

Test the ohms of the circuit with an ohmmeter to see if the relay is capable of supplying the power required to start the diesel engine. A functional relay will have a resistance of 50 to 120 ohms. The relay is questionable if the circuit produces less than 50 ohms.

Testing glow plugs

5th Step

To test each pin for voltage and/or power, use a relay socket: 30 must show battery voltage, 50 must show power when the engine is running, 85 must show battery voltage, 86 must show power when the key is turned to the pre-glow slot, 87 must-have direct power to the plugs, L must show that power is sent to the dashboard LED, and T must show that the temperature sender is receiving input from the cylinder head. The relay is not working properly if any of these pins are not receiving or delivering voltage and/or power.

6th Step

Check the fusible link for any loose wires or nuts, as well as unclean contacts.

Glow plug control module

Connect the glow plug to the dashboard LED with a wire. The relay is defective if you hear clicking and watch the light turn on and off but there is no electricity reaching the glow socket.

How To Clean Glow Plugs In A Diesel Engine Mercedes Benz Sprinter

Diesel engines are naturally dirtier than conventional gasoline engines. Diesel fuel has a lower refinement level than gasoline. Impurities in the gasoline may form as a result of this. An oil leak in the engine might also cause the glow plugs to foul. Furthermore, carbon buildup from the plug's typical heat cycle might cause it to get dirty. The glow plugs will need to be cleaned if this happens.

Combustion system

1st Step

Disconnect the glow plug wire from the engine. Although you will be cleaning all of the plugs, you should begin by cleaning one plug at a time. Remove the top of the plug wire from the engine. You may need to carefully twist the plug wire back and forth as you draw it up, but it should come out easily.

2nd Step

Lower the glow plug socket into the plug well after attaching it to the socket extension.

3rd Step

Place the wrench in such a way that the socket clutches the top of the plug.

4th Step

To remove the socket (and plug), use a socket wrench to turn it counterclockwise.

Replacing glow plugs

5th Step

Examine the electrode on the plug's bottom to ensure it is not damaged. Remove the plug from its socket and thoroughly clean it with brake parts cleaning. This will clear any loose carbon deposits or oil from the plug's bottom. Allow the plug to dry naturally.

6th Step

Reinstall the glow plug, tighten it, and attach the plug wire over it.

For each glow plug, repeat steps 1 through 6.

How To Replace Mercedes-Benz Glow Plugs: A Step-by-Step Guide

What Tools Do You Need to Replace Your Glow Plugs?

Fulty glow plug

Checking the condition of your glow plugs regularly and replacing them as needed can maintain your engine in great shape. To replace your glow plugs, you'll need the following items:

  • Torque wrenches, socket wrenches, and ratchets are all the necessary manual tools.
  • Pliers
  • Screwdriver
  • Reamer for glow plugs
  • Glow plugs that have been replaced

Glow Plug Replacement In 7 Easy Steps

1st Step: The Battery Cable Must Be Disconnected

Disconnect the black negative battery cable by opening the bonnet. Because glow plugs draw the entire 12 volts from the battery, this is an important safety measure. To release the nut that links the cable to the negative terminal, you may require a wrench.

Glow plug warning light

2nd Step: Remove The Valve Cover From The Glow Plugs

You'll need to remove the valve cover if your glow plugs are protected by one. Remove the retaining screws around the outside edge of the cover and inspect it for damage before replacing it.

3rd Step: Remove The Valve Cover From The Valve

The glow plug wires must be disconnected. The glow plugs are located in the cylinder head and are connected to a wire that supplies the 12-volt power source. Nuts, bolts, terminals, or other similar connection devices will be used to connect the wires to the plugs.

When removing tight terminals, pliers can be useful.

4th Step: Glow Plug Wires Should Be Removed

The glow plug wires must be disconnected. The glow plugs are located in the cylinder head and are connected to a wire that supplies the 12-volt power source. Nuts, bolts, terminals, or other similar connection devices will be used to connect the wires to the plugs.

Glow plug module

When removing tight terminals, pliers can be useful.

5th Step: Glow Plugs Should Be Removed

Using a socket and a ratchet, remove the glow plugs. Place the ratchet over each plug and rotate it clockwise. To loosen the plugs, you may need to attach a deep well socket to the socket wrench.

You'll be able to assess the condition of each light plug after you've removed it. Glow plugs can break down once installed, so make sure you get all the components out of the engine before removing a broken one.

6th Step: Put The New Glow Plugs In Place

Install the new glow plugs by hand, placing them and tightening them with a wrench in a clockwise motion. Overtightening the plugs might cause them to shatter, so be careful.

New glow plugs

7th Step: Connect The Cables Again

Reconnect the glow plug wires, securing the nuts, bolts, or terminals with a tool.

Reinstall the valve cover. You can read your Mercedes-Benz Sprinter owner's manual to see whether the valve sockets need to be torqued to a certain pressure.

To test your new glow plugs, connect the battery cable and start your engine. You can also test your plugs with a scan tool.

When Should Your Glow Plug Control Module Be Replaced?

Changing your glow plugs or glow plug control module is a simple task that should be done every 60,000 miles (95,000 km). This will assist you to avoid discovering they've gone rotten on a bitterly chilly day.

The bonnet

Before you begin, make sure you have read all relevant instructions in your owner's manual and that you have all the necessary tools.


Because diesel engines lack spark plugs or any type of ignition system, it is up to the glow plugs to start the engine when it is cold or outside. As a result, Diesel glow plugs have a long service life and must be replaced regularly.

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