In this Service Information bulletin, we would like to inform you about a number of basic functions that have been updated in the following engine software release.
Control unit variant:
M 270 with VC7 u10
M 274 with VC8 u8
Driving mode
Run gas reservoir empty:
The gas reservoirs are run empty and automatic switchover to gasoline operation occurs at a fill level of approx. 5.8 %, gas reservoir pressure of 10 bar (depending on the ambient temperature).
The operating mode switchover is indicated in the instrument cluster.
At a gasoline fill level below 7 l, a small quantity of natural gas is additionally injected (mixed-fuel mode) in order to increase the range of gasoline operation. This is stopped at a residual gas quantity of approx. 2 % and the gas shutoff valve is closed so that no vacuum can be created in the gas reservoirs.
The gasoline reserve indicator is displayed at a fill level of approx. 6 l.
After refueling with natural gas
After each gas refueling procedure, the vehicle starts in gasoline mode until the lambda control becomes active. When the vehicle switches back to natural gas operation a few seconds after the engine is started, a gas quality check is performed so that the vehicle always starts properly even with varying gas types (H-gas/L-gas).
The operating mode switchover is indicated in the instrument cluster.
Since the vehicle is usually already at operating temperature when refueling takes place, the switchover to natural gas operation usually takes place before the vehicle has left the filling station. Once the quality of the newly tanked gas has been adapted, the vehicle will always start in natural gas mode until the next refueling procedure.
Following the gas refueling procedure, the vehicle briefly switches over to gasoline operation once reaching operating temperature in order to additionally perform gasoline mixture adaptation and to ensure that the gasoline system is ready for operation. If this procedure is interrupted, adaptation is repeated during the next driving cycle.
The operating mode switchover is indicated in the instrument cluster.
After multiple natural gas refueling procedures
Following multiple natural gas refueling procedures - without fuel consumption in between - a longer phase (several km) in gasoline mode may occur in which mixture adaptation as well as quantity correction of the injection nozzles take place.
The operating mode switchover is indicated in the instrument cluster.
Key-start
A regular engine start is always performed in gasoline mode unless special circumstances prevent this, e.g.:
New refueling procedure
Coolant temperature < -15 °C
ECO start/stop function
ECO start/stop function
Whenever the engine is started from the automatic ECO start/stop function, a number of gasoline injections take place during the engine acceleration phase in order to ensure a faster and more comfortable start. When idle speed is reached or when the vehicle starts off, natural gas operation is already fully active again. The switchover is not noticeable and is not indicated.
The operating mode switchover is not indicated in the instrument cluster.
Cold start at low temperatures
At a coolant temperature below -15 °C, the engine is started in gasoline mode and switches over to natural gas operation after a short distance or warm-up phase.
The operating mode switchover is indicated in the instrument cluster.
As soon as the gas temperature in the rail drops below -30 °C, natural gas operation is prevented and the engine switches over to gasoline operation. If the gas rail temperature reaches > -30 °C and simultaneously a coolant temperature of > 55 °C, the engine switches back to natural gas operation.
The operating mode switchover is indicated in the instrument cluster.
Operation under high load or on uphill stretches
In the case of long natural gas operation with extremely high engine load (e.g. uphill stretches, journeys with trailer), the engine temporarily switches over to gasoline operation in order to prevent the gasoline injection components from exceeding maximum component temperatures.
The operating mode switchover is indicated in the instrument cluster.