Fault in detecting coolant temperature function

P83.70-2221-09

1 Burner housing

2 Heat exchanger

3 CAN bus

A6/1 STH radio remote control receiver

N22 AAC pushbutton control module

S46 STH switch

Y23 STH fuel metering pump

A6m1 Circulation pump

A6m2 Combustion air blower

A6n1 STH control module

Functional procedure

1 The heater operates in partial load or full load mode. Combustion is stable.

2 Internal coolant temperature acquisition is continuously monitored by the STH control module (A6n1).

3 The STH control module detects a coolant temperature acquisition malfunction:

 The temperature signal has exceeded the temperature acquisition range.

4 The STH control module initializes a malfunction shutoff in order to protect the heater.

5 The STH fuel metering pump (Y23) is switched off, and combustion is interrupted.

6 The STH control module initializes the STH radio remote control receiver (A6/1) with the "Vehicle blower off" signal.

7 The radio remote control receiver reports the end of heater operation to the AAC pushbutton control module (N22) via the CAN bus (3). The pushbutton control module interrupts the initialization of the vehicle blower.

8 Heater disturbance run-on occurs for approx. 120 s.

9 Heater run-on, and therefore malfunction shutoff, are terminated. The combustion air blower (A6m2) and the recirculation pump (A6m1) are switched off. The green telltale in the STH switch (S46) is extinguished.

 In order to recommission the heater, this must be switched off and on again following the eradication of the trouble source.