D. Symptoms of Some Faults Diagnosable From OP Pattern

D. Symptoms of Some Faults Diagnosable from Operating Pattern

1. Fuse for rear fan motor defective

Starting position: Heater fan switch position 3- 4 and temperature switch "max cold".

Test Step: Set temperature switch to "max heat".

Result: Heater fan off. Cars with control unit part number "...01 ": fan switches to half value. 911 turbo:
Fan speed decreases only on side of the defective rear fan.

Remark: To determine acoustically reduced fan speed, open only the two side air vents. Close all other vents.

Switch back temperature control to "max cold.". Heater fan switches on again.

Fault Rear fan speed "1" seized;
Memory: present Code 43/46 and Rear fan speed "2" seized; (not) present Code 44 (47)


2. Rear Fan Motor or Wiring Plug Defective

Starting position: Heater fan switch position 3- 4 and temperature switch "max. cold".

Test Step: Set temperature switch to "max. heat"

Result: Heater fan off. Cars with control unit part number "...01 ": fan switches to half value. 911 turbo:
fan speed decreases only on side of the defective rear fan. Switch back temperature control to "max. cold". Heater fan switches on again.

Fault Rear fan motor speed "1"
Memory: positive short present Code 43
(46) and Rear fan speed "2"
seized; (not) present Code 44
(47).

3. Rear Fan - Resistor Open Circuit

Starting Position: Heater fan switch position 1, 4, temperature switch "max. cold", all air vents closed, only one center vent open.

Test Step: Set temperature switch to "max heat".

Result: Heater fan off. Rear fan motor speed "2". After 5 seconds, rear fan switches off for 1 second. After an additional 5 seconds, heater fan switches on again.

Fault Rear fan speed "1" seized (not)
Memory: present. Code 43 (46)

4. Rear Fan Motor - NTC Open Circuit

Starting position: Engine cold, fan switch position "1", temperature switch "max. cold".

Result: Rear fan operates in speed "1" only.

Fault Temperature sensor, rear fan
Memory: motor open circuit present Code 15