The alternative fuels engine control module (AF ECM) controls alternative fuel engine operation. The control module 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 Alternative Fuels ECM also runs tests (DTCs) on various sensors and outputs. If a DTC detects a problem, the Alternative Fuels ECM will store the DTC number along with sensor information retrieved at the time of the problem (Freeze Frame). The DTC number and any Freeze Frame information can be retrieved from the Alternative Fuels ECM using a scan tool.
The Alternative Fuels 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 31 kPa | 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 close the low pressure lock-off (LPL) solenoid. 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 30 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 3,000 RPM. | The AF ECU limits vehicle speed. The Alternative Fuels ECM will close the low pressure lock-off when the enable conditions are met. When vehicle speed indicates 151 km/h (94 mph) or less, the Alternative Fuels ECM will open the MCV. The engine will operate in Open Loop mode during Speed Limiting. | ||||||||||
RPM Limiting | Engine speed indicates more than 5,500 RPM | The Alternative Fuels ECM limits engine speed. The Alternative Fuels ECM will close the low pressure lock-off when the enable conditions are met. When engine speed indicates 5,475 RPM or less, the Alternative Fuels ECM will open the low pressure lock-off. The engine will operate in Open Loop mode during RPM Limiting. | ||||||||||
Fuel Switch-Over to Gasoline |
| The Alternative Fuels ECM will switch-over to gasoline operation when any ONE of the enable conditions are met. If low FPS voltage caused the fuel switch-over, the Alternative Fuels ECM will not resume alternative fuel operation until the FPS voltage 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. | ||||||||||
Lock-Off Solenoid operation |
| The Alternative Fuels ECM will open only the high pressure lock-off (HPL) solenoids for 1 second after ignition ON. After engine speed of 25 RPM or more is obtained and held, the Alternative Fuels ECM will open the HPLs and the low pressure lock-off (LPL) solenoid. | ||||||||||
Gasoline Start strategy | Every 100 engine starts or when the Engine Coolant Temperature is -12°C (10°F) or less. The Alternative Fuels ECM will switch-over to Alternative Fuel operation under the following deceleration conditions:
The AF ECU will abort the switch-over if the throttle position has increased more than 6 percent during the 500 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. In addition to the gasoline start, the gasoline fuel injectors are pulsed 4 times during EVERY engine start. The Alternative Fuels ECM performs the cold weather gasoline start to aid in startability. Most Alternative Fuels ECM DTCs are inhibited from testing until 5 seconds after a successful switch-over to alternative fuel operation has occurred. The Alternative Fuels ECM CKP sensor circuit performance DTC tests during gasoline operation. |
Additional Description Information
Refer to Powertrain Control Module Description in Engine Controls in the G Van Service Manual for further information that may apply to this vehicle.
