Webasto Thermo Pro 90 Series Service Installations page 19

Thermo Pro 90
5.6 Troubleshooting (fault symptoms)
Symptom
A Heater does not
respond, no component
running, operation indi-
cator remains off
B Heater will not start,
briefly starts up then
switches immediately to
afterrunning, operating
indicator flashing (fault
code output, See Chap-
ter "5.5 Fault code table
(fault codes, flash
codes)" on page 503.
Possible cause Corrective measures
Operating voltage –
–
Operation indicator Operating indicator control element
(control element or ON/ –
OFF switch) –
Operation indicator, switch:
–
–
DP42 fuel pump
Always operate the fuel pump via the heater. Never connect directly to
12V or 24V supply.
–
–
–
–
Combustion air fan –
–
–
U4840 coolant pump –
–
–
–
Coolant temperature –
sensor –
–
Glow plug See symptom A, glow plug
5 Malfunctions and troubleshooting
Check fuses (F2, F3)
Check power supply: measure supply voltage at heater connector X8,
Pin 12 (see Fig. 1112)
(VG connector, See Chapter "9.8.1 Legend to connector
VG95328R2016PN (if installed)" on page 904.
Measure supply voltage at connector X9, Pin 11
Check continuity at connector X9, Pin 12 to ground
Measure supply voltage at switch S4, Pin A
Check continuity at switch S4, Pin F to ground
ATTENTION
Check fuel line connection at fuel pump DP42
Connect Webasto Thermo Test and evaluate.
Ensure clear passage and seating of the flat spring contacts of the fuel
pump line.
Measure cold resistance of fuel pump DP42 at 25 °, see Section 6.4.5
Setpoints: 4.95 to 5.45 ohm, test current: < 1 mA
Check exhaust system and air intake system (see 'Excess smoke from
heater during start-up phase')
Connect Webasto Thermo Test and evaluate.
• Set speed of 5500 rpm
• Listen for grinding noise and start-up noise.
Start up to the specified speed must be heard.
• The error message "Fan motor stiff" must not be activated
Short-circuit or break. Check fan wiring
Check coolant level
Connect Webasto Thermo Test and evaluate.
Switch on component test via Webasto Thermo Test, touch pump
with your hand, the pump is operating if slight vibration can be felt
Check wiring
Check self-bleeding position, see Section 7.5.2
Check coolant level
Connect Webasto Thermo Test and evaluate.
Check cold resistance of coolant temperature sensor, see Section
6.4.1.
Setpoints (at 25 °C): 990 to 1010 ohm, test current < 1 mA
505