5 Faults, Troubleshooting Thermo Pro 90
505
10 Combustion air
fan
Combustion air fan sluggish.
Conduct component test on function of fan motor
with Webasto Thermo Test PC Diagnosis.
– Specify a set-point
speed of 6,000 rpm
– Listen for rubbing and
friction noises.
In addition, start-up
must be audible up to
the specified speed
– No "Sluggish fan start"
fault message may be
output
11 U4846 circula-
tion pump
Check pump for leaks
12 Fuel
connection
Observe fuel fill level and fuel removal from tank
Check integration in vehicle fuel system
Check fuel lines for leaks, kinking and clogging,
especially in the area of the intake-side line connec-
tors
Disconnect the fuel line from the heater, hold the
hose in a catch container and operate the metering
pump with the Webasto Thermo Test PC Diagnosis
for 180 s at 9 Hz. When doing so, watch whether
the fuel is pumped bubble-free
If fuel sprays out of the line when the line is sepa-
rated from the heater, the fuel pipe of the burner
unit is probably clogged. If this is the case, the burner
unit must be replaced.
13 Coolant circuit Check the integration in the vehicle coolant circuit in
accordance with the general installation instructions
Check whether coolant circuit is correctly bled
Check circulation in coolant circuit
14 Coolant circuit Eliminate kinks and rubbing spots
Check leaks on heater, water connection piece, cir-
culation pump and hoses and eliminate
15 Exhaust system
and air intake
system
Check whether intake pipe and exhaust pipe are
routed in accordance with general installation
instructions
Check to make sure lines are not clogged
Eliminate existing leaks on intake pipe and exhaust
pipe (no CO
2
in intake air)
The exhaust pipe outlet may not be routed under the
intake pipe inlet
16 Exhaust system
and air intake
system
Check whether sufficient distance is present to pas-
senger compartment fresh-air intake of vehicle
No exhaust gas may be
sucked in through the com-
bustion air pipe
Error point Component Recommended workshop action Parameter
Fig. 502 Overview of functional test of heater and its components
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