Does Mercedes Benz use a biodegradable electrical wiring harness?

This article will answer the following questions: Does Mercedes Benz use biodegradable electrical harnesses? Where are biodegradable wiring harnesses used in the vehicle? What are the common problems due to biodegradable wiring harnesses? How to identify if the Mercedes Benz has a biodegradable wiring harness? Should you buy a used Mercedes Benz car with biodegradable wiring harnesses?

Does Mercedes Benz use biodegradable electrical wiring harnesses?

Mercedes Benz cars manufactured between 1992 to 1996 have biodegradable electrical wiring harnesses. Biodegradable wiring harnesses were used in the production cars to comply with the environmental norms in the nineties. Delphi was one of the suppliers of electrical wiring harnesses to Mercedes Benz used insulation of the electrical lines made out of biodegradable material instead of traditional non-degradable insulation found on the early cars.

The biodegradable insulations develop cracks and get separated from the electrical lines, completely exposing them. The exposed electrical lines are prone to electrical short circuits if they come in contact with the body and the exposed area can get corroded since it is open to the elements like dust and moisture. Mercedes Benz did not know of these issues and the complaints started to come in after the standard warranty period was over. 

Mercedes Benz quickly rectified the issues and introduced new materials which satisfied the environmental norms and also did not have problems with the biodegradable wiring harnesses. However, there are still models with degrading wiring harnesses in circulation. 

Where are the Biodegradable wiring harnesses used in Mercedes Benz cars?

The biodegradable wiring harnesses manufactured by Delphi were used in the engine wiring harness. The engine wiring harness consists of electrical lines that go to all the sensors and actuators present in the engine. The engine wiring harness performs the crucial task of connecting the control unit to the various actuators and sensors, there are power supply lines which split into multiple points in order to give power supply to all the loads. The throttle valves and the ignition system are the most common areas affected due to the exposed electrical lines as the insulation cracks and falls off the lines. 

What are the common problems caused due to biodegradable wiring harness used in Mercedes Benz?

The common problem caused due to the biodegradable wiring harness used in Mercedes Benz is as follows:

  • Electrical short circuits

The biodegradable material used in the insulation of the electrical lines was based on soya and it had poor resistance to heat. The heat from the engine makes the insulating material hard and over time the insulation simply crumbles away exposing the copper wire. 

Electrical short circuits are created when the exposed copper wire comes in contact with other electrical lines or bodies of the vehicle. There can be a short circuit with the ground or a short circuit with the nearby positive line.

The only way to rectify the short circuit in the electrical circuit is to replace the entire engine electrical wiring harness.

  • Poor idling and misfire.

The vehicle with biodegradable engine wiring harnesses suffered poor idle and stalling as the electrical lines connected to throttle valves were either short or corroded due to the exposed copper lines. Misfiring was also caused due to excessive line resistance in the electrical lines connecting the fuel injector with the electronic fuel injection control unit. 

How to identify if the Mercedes Benz has a biodegradable wiring harness?

Mercedes Benz started using the environment-friendly biodegradable engine wiring harness from Delphi from 1992 to 1996 but the production year alone is not an effective method to identify if the model has an environment-friendly wiring harness. One of the most effective methods is to identify the type of fuel injection system used in the vehicle.

If the vehicle has an electronic fuel injector system called LH Jetronic or Luftmassenmesser Hitzdraht then the vehicle has a biodegradable engine wiring harness. The LH electronic fuel system does not need an engine control unit as it is a pulsed based fuel injection system and the duration of the pulse is determined after the engine load is calculated based on the air mass. A hot filmed air mass sensor is also used to Measure the air going into the system along with a Lambda sensor to make it a closed-loop system.

Overall it was the vehicles with the V8 M119 engine and also a few V12 engines that were affected due to the environment-friendly engine wiring harness.

Should you buy a used Mercedes Benz car with biodegradable wiring harnesses?

Yes, you should buy a Mercedes Benz car manufactured between 1992 -1996 as apart from the wiring harness issues the rest of the cars have superior built quality. There are also no rust issues in the bodywork and the interior trim and panels are long-lasting. 

It is easy to replace a wiring harness, especially in the M119 V8 engines and the replacement wiring harness is updated with a more durable and heat resistant insulation. The parts are also easily available at the authorised dealerships and replacement of the wiring harness does not require the engine to be removed from the vehicle.

If the wiring harness is not renewed and the vehicle is used with the existing harness then breakdowns are just waiting to occur. The vehicle can stall while running and fuel injectors can cause a misfire in multiple cylinders. Therefore before buying any used Mercedes Benz car that is manufactured between 1992-1996, a visual inspection of the engine wiring harness must be performed. Following are the key areas to perform a visual inspection

  • Check insulation on the electrical lines leading to the ignition coils
  • Check insulation on the fuel injector coupler and individual electrical lines under the fuel rail
  • Remove the protective cover on the engine wiring harness and check individual wires for any cracked insulation.

The engine wiring harness is very simple in construction and does not require any disassembly to perform a visual inspection. The engine side wiring harness starts from the main coupler near the firewall on the left side and goes all the way up to the fuel injectors and ignition coils.

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Mercedes Benz was not the only car manufacturer affected by the issues caused due to the use of soy-based insulation in the biodegradable wiring harness. Volvo was also affected in the 1980s and Volvo later introduced a more durable wiring harness with different part numbers. Mercedes Benz also rectified the issue by using different insulating materials in the electrical harness. However, there is no official recall issued for the wiring harness from Mercedes Benz and many customers either replace the defective harness from the dealerships or specialised repair shops at a cheaper price.