Fault In Coolant Temperature Sensing

Fault In Coolant Temperature Sensing, Function

Shown On Models 215, 220:

Operating procedure
1 Coolant temperature > 65 degrees C and < 77 degrees C

2 Depending on heat requirements, the STH heater or heater booster operates in partial-load or full-load mode:
- The STH or heater booster fuel metering pump (Y23) and the combustion air blower (A6m2) deliver at their minimum or maximum speeds and outputs.
- The coolant circulation pump (A6m1) delivers the coolant via the heat exchanger (2) and the heating and cooling circuits.
- The ventilation blower delivers pre-heated air to the interior.

3 The STH or heater booster control module (A6n1) continuously monitors internal coolant temperature acquisition.

4 The STH or heater booster control module (A6n1) recognizes a malfunction in coolant temperature sensing:
- The temperature signal has exceeded the temperature detection range.

5 In order to protect the STH or heater booster heater, the STH or heater booster control module (A6n1) initializes heater malfunction delayed switch-off with subsequent malfunction shutoff for approx. 120 s:
- the STH or heater booster fuel metering pump (Y23) is switched off.

and

- the control and operating module (N18, N22 or N22/7) is actuated via the CAN Class B (CAN B) with the "blower OFF" signal.

6 The control and operating module (N18, N22 or N22/7) switches the ventilation blower off and switches from stationary heating mode to normal operating mode.

7 Malfunction delayed switch-off has finished:
- The combustion air blower (A6m2) and the recirculation pump (A6m1) are switched off.
- The green or red indicator lamp in the STH switch (N72s12 or S46) is extinguished.
Malfunction shutoff is present.

NOTE: In order to restart, the STH heater or heater booster must be switched off and on again at the STH switch (N72s12 or S46) after the malfunction has been remedied.