28 HT 12 Unimog 1.96
8 Operating problems
8.1 General
Operating problems are often the result of incorrect handling of the machine, the use of
unsuitable materials or irregular maintenance.
The following table presents a summary of a range of problems and their probable
causes.
If a problem can only be eliminated through repair, then the responsible Service
Agent must be called in.
8.2 Host vehicle
All defects and faults in the host vehicle must be examined as described in the separate
instruction book for the host vehicle.
During the warranty period, malfunctions must be dealt with by the responsible
SERVICE Agent.
Fault Possible cause Remedy
8.3 Excavator equipment is not workin
1 Unimog power take-off for hydraulic
pump is not working
Determine cause
2 Oil supply to excavator interrupted Check connection
3 Oil supply to hydraulic pump
interrupted
Check lines
4 Main high-pressure relief valve has
failed
Check main high-pressure relief
valve and replace, if necessary
5 Hydraulic pump has failed Have hydraulic pump checked by a
specialist and replace completely, if
necessary
8.4 Unit is working too slowly and system is becoming too hot
1 Main high-pressure relief valve set
too low or faulty
Adjust main high-pressure relief
valves, replace, if necessary
2 Impermissible degree of wear of
hydraulic pump
Replace hydraulic pump
3 Incorrect hydraulic oil Quality of hydraulic oil must
conform to our recommendation
4 Air in hydraulic system Tighten connections with engine off
and system relieved of pressure
8.5 H
draulic c
linders are not functionin
satisfactoril
1 Sleeve sets in hydraulic cylinders
worn
Renew sleeve sets
2 Secondary valves faulty Check secondary valves and
replace if necessary
3 Impermissible degree of leakage of
the control valve
Check control valve, seal and
replace if necessary
8.6 Trouble in the electrical system
1
Lighting does not come on Check cables, connections, etc.
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