BI-Fuel/Alternative Fuels

CIRCUIT DESCRIPTION
The Manifold Absolute Pressure (MAP) sensor is a pressure sensor. The gasoline Control Module (VCM/PCM or ECM) supplies about 5 volts on the MAP sensor reference voltage circuit. The gasoline Control Module also supplies a ground circuit to the MAP sensor. When the manifold vacuum is low, the MAP signal voltage rises to near 4.5 volts. As the manifold vacuum increases, the MAP signal voltage drops to around 1 volt. The gasoline Control Module and the Alternative Fuels ECM monitor the MAP signal circuit voltage and determine the vacuum within the intake manifold.

Certain vehicle models will also use the MAP sensor in order to determine the Barometric Pressure (BARO) when the ignition switch is turned ON and the engine is NOT cranked. This BARO reading may also be updated whenever the engine is operated at Wide Open Throttle (WOT).

This DTC is used to indicate a MAP sensor signal voltage that is below the normal operating range of the sensor.

CONDITIONS FOR RUNNING THE DTC
^ The engine is operating on alternative fuel.
^ The engine speed is greater than 500 RPM.
^ DTCs P0121, P0122, or P0123 are not set.
^ The TP angle is less than 4 percent when engine speed is less than 1,200 RPM.

or

The TP angle is greater than 20 percent when engine speed is greater than 1,300 RPM.

CONDITIONS FOR SETTING THE DTC
The Alternative Fuel ECM monitors a MAP sensor signal voltage of less than 0.098 volts for at least 4 seconds continuously.

ACTION TAKEN WHEN THE DTC SETS
^ The Alternative Fuel ECM will switch-over to gasoline fuel operation.
^ The Alternative Fuel ECM will not attempt alternative fuel operation until the next key cycle.
^ A first failure of this DTC will NOT illuminate the MIL and will store as Last Test Failed but not as History.
^ The Alternative Fuels ECM will illuminate the MIL and store the DTC as History after 2 consecutive drive trips that the diagnostic runs and fails.
^ The Alternative Fuels ECM will record operating conditions at the time the DTC sets. This information will be stored as Freeze Frame data.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The Last Test Failed status will clear when the DTC runs and passes.
^ The Alternative Fuels ECM will turn OFF the MIL after 3 consecutive drive trips that the DTC runs and passes.
^ The History status will clear after 40 consecutive WARM-UP cycles with NO failures of ANY DTC.
^ All DTC Information can be cleared using a scan tool.
^ Interruption of Control Module (AF ECM I VCM I PCM or ECM) power or ground MAY clear DTC Information. Clearing DTC Information with this method is in-consistent and should not be performed.

DIAGNOSTIC AIDS

Intermittent Condition
A fault not present indicates the condition that caused the DTC to set is intermittent and not currently present. Refer to the Intermiffent Conditions diagnostic information located in Symptoms - Computers and Control Systems. If any additional DTCs were stored proceed to the applicable DTC table in the order stated in Diagnostic System Check - Alternative Fuels (Computers and Control Systems). Initial Inspection and Diagnostic Overview Intermittent Conditions

TEST DESCRIPTION

Steps 1-9:

Steps 10-14:

The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if the failure condition affects the gasoline Control module.
3. This step determines if the failure condition is present.
5. This step determines if the MAP sensor is the cause of the condition.
6. This step determines if the 5-volt reference circuit is the cause of the condition. 4.8 volts is the minimum output that the gasoline Control Module should supply on the 5-volt reference circuit.