Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Glow-plug System: Notes
The glow-plug system is responsible for providing reliable cold start properties and smooth operation when the engine is cold.
The DDE control module sends the temperature requirement of the heater plug to the heating control unit. The heating control unit implements the request and actuates the heater plugs with a pulse-width modulated signal.
The heating control unit additionally sends diagnosis and status information via the LIN-bus connection back to the digital diesel electronics.
| Index | Explanation |
|---|---|
| 1 | Glow plugs |
| 2 | Glow plug control module |
| Index | Explanation |
|---|---|
| 1 | DDE |
| 2 | GSG |
| 3-8 | Glow plugs (Cylinders 1-6) |
The LIN-bus is a bi-directional data interface that operates in accordance with the master/slave principle. The DDE control unit is the master.
Each of the six heating circuits can be diagnosed individually.
When the heating control unit is switched on for the first time, the electrical resistance of the heater plugs is evaluated at the start of the heating process. A hot heater plug has a much higher resistance than a cold plug. If hot heater plugs are detected based on their resistance, less power is applied to the heater plugs at the start of the heating cycle.
If, on the other hand, cold heater plugs are detected, the maximum power is applied to the heater plugs at the start of the heating cycle. This function is known as dynamic repeat heating. This function avoids the situation where too much power is applied to a heater plug, which is already hot, as the result of a second heating cycle following shortly after the first, and therefore overheats.
The DDE control unit determines the necessary heater plug temperature as a function of the following operating values:
- Engine speed
- Intake air temperature
- Injected quantity
- Ambient pressure
- System voltage
- Status signal, starter enable.
The digital diesel electronics sends the required heater plug temperature to the heating control unit to activate heating.
The heating system assumes various operating modes that are explained in the following.
NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.