Diagnose
Status September 2003 (EvoBus-Service / AFT)
Page: 71 of 83
4.3
EGM-specific Customer Service routines
Special routines have been realised for simplified handling or troubleshooting on the M 447 hLAG natural-
gas engine which can be carried out with the customer service tool "StarDiagnosis".
4.3.1
Temporarily switch off LMR
The M 447 hLAG is a lean engine. The lambda probe is a lean probe from Bosch with a measuring range
between 0.7 and 1.9. Normally, the lambda controller works in fired operation. A very significant output
variable of the lambda controller is the Lambda correction factor . The lambda correction factor is
monitored by the EGM (Lambda control diagnosis). In the case of a fault, the event: "Mixture formation:
control deviation too great" is detected, the fault code 0775 is stored in the fault memory and the
corresponding engine protection is activated.
The fault code 0775 means that a serious fault is present in the mixture forming system – however, it
does not provide any localising information on possible fault causes.
Possible causes of this fault may be:
•
Fault in mixture formation
-
Mechanical defect of one or several gas injectors (
Æ
gas injector sticks open, gas injector does
not open correctly, leaks on injector block etc.)
-
Failure of ignition on one or several cylinders (
Æ
mixture leaning due to excess oxygen)
-
Faulty signal of boost pressure sensor (
Æ
faulty air mass detection with the consequence of
incorrect gas mass calculation)
-
Faulty signal of gas pressure sensor (
Æ
faulty gas-injection time calculation)
•
Fault in lambda determination
-
Faulty signal of lambda sensor (
Æ
unmetered air in exhaust section, defective probe etc.)
The Customer Service routine: "Temporarily switch off LMR" can help localise the fault source with regard
to mixture formation OR lambda determination. The Customer Service routine "Temporarily switch off
LMR" enables the lambda controller to be switched off for a limited time. The engine then runs controlled
and without power restrictions – the lambda measurement continues to be taken. If the engine runs
properly in controlled operation, then this is a sure sign that the engine malfunction results from faulty
determination of the actual lambda. In the opposite case, the fault must be sought in the mixture
formation system.
Notes:
-
The lambda controller can be switched off and on again with StarDiagnosis.
-
The lambda controller can only be switched off temporarily, i.e. the lambda controller is switched off
for a maximum period of 10 min. or until the ignition is switched off.
