The Alternative Fuels Engine Control Module (ECM) controls alternative fuel engine operation. The ECM monitors various engine and vehicle functions to provide the correct amount of fuel under all operating conditions. This provides excellent driveability and fuel economy while maintaining exhaust emission levels. Refer to Engine Controls Component Views for location views.
In addition to controlling engine operation, the ECM also runs tests (DTCs) on various sensors and outputs. If a DTC detects a problem, the ECM will store the DTC number along with Freeze Frame sensor information retrieved at the time of the problem. The DTC number and any Freeze Frame information can be retrieved from the ECM with a scan tool.
The ECM operates in several Function modes which are defined in the Alternative Fuels ECM Function Parameters table.
Function | Enable Conditions | Function Description | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Deceleration Fuel Cut-Off (DFCO) |
The Alternative Fuels ECM will exit DFCO when MAP is greater than 30-34 kPa depending on BARO | During extended decel operation, the vehicle's exhaust catalyst temperature may exceed maximum limits. In order to cool the exhaust catalyst, the Alternative Fuels ECM will turn OFF the CNG fuel injectors. With fuel flow stopped during the DFCO enable conditions, the catalyst's temperature can be reduced. | ||||||||||||||||||
Deceleration Open Loop |
| During normal decel conditions, the Alternative Fuels ECM will operate the engine in Open Loop mode. If the enable conditions are met for greater than 3 seconds, the Alternative Fuels ECM will transition to the DFCO mode. | ||||||||||||||||||
Speed Limiting | The vehicle speed sensor (VSS) indicates a vehicle speed of 156 km/h (97 mph) or more with an engine speed greater than 2,000 RPM. | The Alternative Fuels ECM limits vehicle speed. The Alternative Fuels ECM will turn OFF the CNG fuel injectors when the enable conditions are met. When vehicle speed indicates 151 km/h (94 mph) or less, the Alternative Fuels ECM will open the CNG fuel Injectos. The engine will operate in Open Loop mode during Speed Limiting. | ||||||||||||||||||
RPM Limiting | Engine speed indicates more than 5,750 RPM in Drive OR Engine speed indicates more than 3,100 RPM in Park/Neutral | The Alternative Fuels ECM limits engine speed. The Alternative Fuels ECM will turn OFF the CNG fuel injectors when the enable conditions are met. When engine speed indicates less than 5,476 RPM in Drive or 3,051 RPM in Park/Neutral, the Alternative Fuels ECM will open the CNG fuel injectors. The engine will operate in Open Loop mode during RPM Limiting. | ||||||||||||||||||
Fuel Switch-Over to Gasoline-KL6 models |
| The Alternative Fuels ECM will switch over to gasoline operation when any ONE of the enable conditions are met. If low FTP values caused the fuel switch over, the Alternative Fuels ECM will not resume alternative fuel operation until the FTP sensor exceeds 1.50 volts (6,890 kPa@21°C [1,000 psi@70°F]). | ||||||||||||||||||
Open Loop mode |
| During Open Loop mode, the Alternative Fuels ECM will disable both Short and Long Term Fuel Trim. Short Term Fuel Trim will be reset. The Alternative Fuels ECM will fuel the engine based upon the Long Term Fuel Trim recorded prior to Open Loop mode. | ||||||||||||||||||
Closed Loop mode |
Both above conditions are complete | The Alternative Fuels ECM will determine the amount of time the engine must continuously operate based upon coolant temperature. The colder the coolant temperature the longer the time delay. The Alternative Fuels ECM will determine the amount of delay time based upon the O2 sensor activity. The more active the O2 sensor the shorter the delay time. | ||||||||||||||||||
Catalyst Over-Temperature (COT) Protection |
Above conditions are present for more than 10 seconds. | During extended open throttle operation the vehicles exhaust catalyst temperature may exceed maximum limits. In order to cool the exhaust catalyst, the Alternative Fuels ECM will operate in open loop. In addition, the Alternative Fuels ECM will lean the fuel mixture from 4.6 to 15 % depending on airflow. When an engine speed of less than 3,600 RPM is obtained the Alternative Fuels ECM will stop COT operation | ||||||||||||||||||
Lock-Off Solenoid operation |
| The Alternative Fuels ECM will open only the high pressure lock-off (HPL) solenoid for 1 second after ignition ON. When an engine speed of 25 RPM or more is obtained and held, the Alternative Fuels ECM will open the HPL and the low pressure lock-off (LPL) solenoid. | ||||||||||||||||||
Gasoline Start strategy-KL6 Models | Every 100 engine starts The Alternative Fuels ECM will return to CNG operation under the following deceleration conditions:
The Alternative Fuels ECM will abort the return to CNG operation if the throttle position has increased more than 6 percent during the 100 ms switch-over period | The Alternative Fuels ECM performs the gasoline start every 100 engine starts to allow the gasoline injectors to operate. This increases injector reliability. Most Alternative Fuels ECM DTCs are inhibited from testing until 5 seconds after a successful return to CNG operation has occurred. The Alternative Fuels ECM CKP sensor circuit performance DTC tests during gasoline operation. |
