To ease the starting sequence and to secure an engine start below 0°C, glow plugs are used. Their task is to raise the temperature in the combustion chamber at the point where the diesel injection occurs.

Glow plugs have a very low resistance. In cold condition they have around 0,3Ω - 1Ω, this changes very fast with the rising temperature. This low resistance allows a high current to flow.
The task of the glow plug relay is not just to switch the current on and off.
Depending on the model year of the vehicle they are built-in and the type of used glow plugs, there are several timings to be considered. Additionally the temperature influences these timings:

• Pre-Heating Time
• Heating Time
• Post-Heating Time

The first units use internal timings for heating and only check the temperature to variegate these timings. At these units the current is switched with real relays.
Some units use 2 relays to handle the high current.

Newer units starting from around 2001, are completely controlled by the Electronic Diesel Control (EDC). Their communication is realized with a bus signal. These units are able to check if the glow plugs are defective. In these GPRs semiconductors are used instead of relays.

At the newest glow plug relays, starting from around 2007, the bus communication is realized with a LIN protocol. These have an advanced failure check mode.8

Today our product portfolio consists of 222 glow plug relays which cover a total of 16.697 vehicle types.