Used for pre-heating in diesel engines (pre-heating time). The pre-heating relay (control unit, glow time) has the function of switching the current for the glow plugs on and off in a time-controlled and temperature-dependent manner.

Ignition on. Preheating time (Kl H) and glow control display (Kl L) begins.
After the temperature-dependent glow control display has expired, it goes out, signaling the start release. After a successful start (engine running), the relay remains closed for a further 20s (+/- 3) (afterglow time).
If there is no start after the glow control display has gone out, the preheating process is aborted after the safety switch-on time of approx. 20s (+/- 3).
At relay temperature +10°C (+/- 5) glow stop, i.e. the relay is without function.

Service – test area:
Check the above function by connecting terminal R to ground; also possible after exceeding the glow stop temperature.