BI-Fuel/Alternative Fuels

CIRCUIT DESCRIPTION
The Intake Air Temperature (IAT) sensor is a thermistor. The IAT 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 IAT signal circuit. The gasoline Control Module also supplies a ground circuit to the IAT sensor. When IAT resistance is high (cold sensor), the IAT signal voltage remains near the supplied 5 volts. As the IAT 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 IAT signal circuit voltage in order to determine the temperature of the air entering the engine.

This DTC is used to indicate an IAT signal circuit voltage that is above the normal operating range of the sensor.

CONDITIONS FOR RUNNING THE DTC
^ The engine is operating on alternative fuel.
^ The engine has been operating for greater than 1.5 minutes when the engine start-up temperature is greater than 0°C (32°F).

or

^ The engine has been operating for greater than 10 minutes when the engine start-up temperature is 0°C (32°F) or less.
^ The vehicle speed is less than 1.6 km/h (1 mph) for at least 10 seconds continuously.
^ Calculated air flow is less than 250 grams per second for at least 10 seconds continuously.

CONDITIONS FOR SETTING THE DTC
The Alternative Fuels ECM monitors an IAT sensor signal voltage greater than 4.80 volts for at least 5 seconds continuously.

ACTION TAKEN WHEN THE DTC SETS
^ 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/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

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 1-11:

Steps 12-17:

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 IAT sensor is the open condition.
6. This step determines if the sensor ground circuit is the open condition.
7. This step determines if the IAT signal circuit wiring is the open condition.
11. If the connector terminals pass inspection test the sensor signal circuit for a short to a 5 volt reference circuit. Although an unlikely failure, this condition should be diagnosed before replacing the gasoline Control module.