Thermo Pro 90 5 Faults, Troubleshooting
508
3 Supply voltage
too high/Operat-
ing voltage too
low
Power supply Check battery
Check electrical connections
4Flame was
detected prior to
combustion
Exhaust temperature sensor
defective
Functional check of exhaust temperature sensor; replace
exhaust temperature sensor if necessary
5 Not available Not available Not available
6 Coolant temper-
ature sensor
defective
Wiring Check wiring for damage, open circuit and short circuit
Coolant temperature sen-
sor defective
Functional check of coolant temperature sensor; replace if
necessary
7 Metering pump
defective
Wiring Check wiring for damage, open circuit and short circuit
Metering pump defective Functional check of metering pump; replace metering
pump if necessary
8 Combustion air
fan defective
Wiring Check wiring for damage, open circuit and short circuit
Combustion air fan is
blocked
Functional check of combustion air fan; replace combus-
tion air fan if necessary
Combustion air fan defec-
tive
Replace combustion air fan
9 Glow plug defec-
tive
Wiring Check wiring for damage, open circuit and short circuit
Glow plug defective Functional check of glow plug; replace glow plug if neces-
sary
10 Overheating Heater overheated Check coolant level, bleed coolant circuit
Check circulation pump for operation
Coolant temperature sen-
sor defective
Check wiring for damage, open circuit and short circuit
Functional check of coolant temperature sensor; replace if
necessary
Overheating protection
defective
Check wiring for damage, open circuit and short circuit
Functional check of overheating protection; replace if nec-
essary
11 Circulation pump
defective
Wiring Check wiring for damage, open circuit and short circuit
Circulation pump defective Replace circulation pump
12 Battery main
switch short cir-
cuit
Wiring Check wiring for damage, open circuit and short circuit
Electronic battery switch
defective
Replace electronic battery switch (S10, see Chap. 7)
13 Output vehicle
fan short circuit
Wiring Check wiring for damage, open circuit and short circuit
Vehicle fan relay Check wiring for damage, open circuit and short circuit
Functional check of vehicle fan relay (K5, see Chap. 7);
replace vehicle fan relay if necessary
14 Overheating pro-
tection defective
Wiring Check wiring for damage, open circuit and short circuit
Overheating protection
sensor defective
Functional check of overheating protection sensor; replace
if necessary
15 Reference resist-
ance not reached
during start
Wiring Check glow plug wiring for damage, open circuit and short
circuit
Glow plug defective Functional check of glow plug; replace glow plug if neces-
sary
Error code
number/
Number of
flashing
pulses
Fault message Possible causes Recommended workshop action
Fig. 503 Error code output by standard timer/switch
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