AVL DiGas 4000 - Page 120

4-/5-Gas Measuring Instruments Unit AVL 4000
5-24 Service Manual
Primary error symptom Primary cause
(of error)
Secondary cause of
error
Possible tests/
establishing cause
Remedy
NO measurement
value slow
Measurement
without exhaust
gas (i.e. fresh air)
over long period
Exhaust gas
measurement over
long period with not
very much oxygen
Carry out
measurements with
different NO concen-
trations or replace
NO sensor
NO measurement
value high and/or
fluctuating
significantly
Sulphurous exhaust gas,
internal sulphur adsorber filter is full
Replace NO sensor
Leak in exhaust
pipe
O
2
measurement
value too high?
(only applies to 4-
stroke engines and
lambda setpoint
≤ 1)
Lambda value >
setpoint (generally
applies)
CO + CO
2
-
measurement value
less than 15 % by
vol.?
If less than 14 %,
probably a leak in
exhaust pipe or
probe (for 4-stroke
only, lambda
≤ 1)
Repair leak in
exhaust
Caution: some
engines add fresh air
externally to the
exhaust! In such
cases, the criterion
does not apply.
Leak in probe or
probe hose
O
2
measurement
value too high?
Carry out leak test Repair leak
Lambda measurement
value incorrect
Hose disconnected
after O
2
sensor
Exhaust gas is
mixed with air due
to pulsations
At least 10 cm hose
is necessary after O
2
sensor (465)
Connect hose to
outlet