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 the IAT sensor is cold, resistance is high and 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 with a scan tool. |
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 - Engine Controls. If any additional DTCs were stored proceed to the applicable DTC table in the order stated in Diagnostic System Check - Alternative Fuels (Engine Controls) .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step determines if the failure condition affects the gasoline Control module.
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This step determines if the failure condition is present.
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This step determines if the IAT sensor is the open condition.
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This step determines if the sensor ground circuit is the open condition.
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This step determines if the IAT signal circuit wiring is the open condition.
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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.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Alternative Fuels Engine Controls Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) |
Does the IAT sensor data parameter indicate IAT temperature colder than the specified value? | -34°C (-27°F) | Go to Step 5 | Go to Step 3 | |
Does the IAT sensor data parameter indicate IAT voltage greater than the specified value? | 4.8 V | Go to Step 12 | Go to Step 4 | |
4 | The fault is not present. Refer to Diagnostic Aids. Are any DTCs stored that have not been diagnosed? | -- | Go to Intermittent Conditions | |
If the fuse of the jumper opens, repair the short to voltage on the IAT sensor signal circuit. If a short to voltage condition is observed, inspect the sensor for an open condition after the wiring repair is completed. Does the IAT sensor data parameter indicate IAT temperature warmer than the specified value? | 148°C (298°F) | Go to Step 8 | Go to Step 6 | |
Connect the fused jumper between the IAT signal circuit and a known good ground. Does the IAT sensor data parameter indicate IAT temperature warmer than the specified value? | 148°C (298°F) | Go to Step 9 | Go to Step 7 | |
Is IAT signal circuit continuity indicated? | -- | Go to Step 11 | Go to Step 10 | |
8 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement in the Engine Controls section of the G Van Service Manual. Is the replacement complete? | -- | Go to Step 17 | -- |
9 | Repair the open sensor ground circuit between the IAT sensor connector and the gasoline Control module. Is the circuit repair complete? | -- | Go to Step 17 | -- |
10 | Repair the open IAT signal circuit between the IAT sensor connector and the gasoline Control module. Is the circuit repair complete? | -- | Go to Step 17 | -- |
Was a terminal repair made? | -- | Go to Step 17 | Go to Step 15 | |
12 |
Is IAT signal circuit continuity indicated? | -- | Go to Step 13 | Go to Step 14 |
13 |
Was a terminal repair made? | -- | Go to Step 17 | Go to Step 16 |
14 | Repair the open IAT signal circuit between the IAT signal circuit splice and the Alternative Fuels ECM. Is the circuit repair complete? | -- | Go to Step 17 | -- |
15 |
Important: The following Control Module replacement procedures must all be completed before attempting to operate the vehicle. The following procedures are located in the G Van Service Manual.
Important: In order to perform the variation learn procedure a switch-over to gasoline operation is necessary. Remove the CNG 20-amp fuse in order to perform the switch-over. Is the replacement complete? | -- | Go to Step 17 | -- |
16 |
Is the replacement complete? | -- | Go to Step 17 | -- |
17 |
Did this DTC run and pass? | -- | System OK | Go to Step 2 |
