BI-Fuel/Alternative Fuels

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor. The ECT thermistor has high resistance when cold and low resistance when hot. The gasoline Control Module (VCM/PCM or ECM) supplies about 5 volts on the ECT signal circuit. The gasoline Control Module also supplies a ground circuit to the ECT sensor. When the ECT resistance is high (cold sensor), the ECT signal voltage remains near the supplied 5 volts. As the ECT sensor warms and resistance drops, more signal circuit voltage is pulled lower to the sensor ground. The gasoline Control Module and the Alternative Fuels ECM monitor the ECT signal circuit voltage in order to determine the engines temperature.

This DTC is used to indicate an engine coolant temperature that is less than the temperature necessary to enable AF ECU Closed Loop fuel control.

CONDITIONS FOR RUNNING THE DTC
^ The engine is operating on alternative fuel.
^ DTCs P0112, P0113, P0117, or P0118 are not set.
^ This DTC has not tested this ignition cycle.
^ The engine has been operating for greater than 8.5 minutes.
^ The vehicle speed is greater than 8 km/h (5 mph).
^ The desired gas flow is greater than 0.5 grams per second.
^ The Intake Air Temperature (IAT) is greater than -15°C (5°F).
^ The ECT at engine start-up is between -17 to +33°C (1-91°F).

CONDITIONS FOR SETTING THE DTC
The Alternative Fuels ECM monitors an engine coolant temperature that has NOT increased above the start-up temperature by 25°C (77°F).

ACTION TAKEN WHEN THE DTC SETS
^ The Alternative Fuels ECM will illuminate the MIL and store the DTC as History during 1 drive trip in which 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/VCM/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
The most likely cause of this DTC is an improperly operating engine coolant system and thermostat. Go to Thermostat Diagnosis in the Cooling System section of the gasoline service in order to verify proper cooling system and thermostat operation.

Intermittent Condition

A fault not present indicates the condition that caused the DTC to set is intermittent and not currently present. Refer to the Intermittent 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 1-7:

Steps 8-11:

The numbers below refer to the step numbers on the diagnostic table.
2. Ensure that the engine can reach proper operating temperature in a timely manner before continuing with ECT sensor diagnosis.
3. This step determines if the Alternative Fuels ECM can monitor an open ECT signal circuit (high voltage).
4. This step determines if the Alternative Fuels ECM can monitor a shorted ECT signal circuit (low voltage).
5. This step determines if the ECT sensor is accurately monitoring engine coolant temperature.