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 sensor is cold, resistance is high and 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 ECT 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 5 seconds when the intake air temperature (IAT) is greater than 0°C (32°F). |
| or |
| The engine has been operating for greater than 10 minutes when the IAT is less than 0°C (32°F). |
Conditions for Setting the DTC
The Alternative Fuels ECM monitors an ECT sensor signal voltage of greater than 4.8 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 ECT 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 ECT 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 ECT sensor data parameter indicate ECT temperature colder than the specified value? | -34°C (-27°F) | Go to Step 5 | Go to Step 3 | |
Does the ECT sensor data parameter indicate ECT 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 ECT 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 ECT sensor data parameter indicate ECT temperature warmer than the specified value? | 148°C (298°F) | Go to Step 8 | Go to Step 6 | |
Connect the fused jumper between the ECT signal circuit and a known good ground. Does the ECT sensor data parameter indicate ECT temperature warmer than the specified value? | 148°C (298°F) | Go to Step 9 | Go to Step 7 | |
Is ECT signal circuit continuity indicated? | -- | Go to Step 11 | Go to Step 10 | |
8 | Replace the ECT sensor. Refer to Engine Coolant 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 ECT sensor connector and the gasoline Control module. Is the circuit repair complete? | -- | Go to Step 17 | -- |
10 | Repair the open ECT signal circuit between the ECT 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 ECT signal circuit continuity indicated? | -- | Go to Step 14 | Go to Step 13 |
13 | Repair the open ECT signal circuit between the ECT signal circuit splice and the AF ECU. Is the circuit repair complete? | -- | Go to Step 17 | -- |
14 |
Was a terminal repair made? | -- | Go to Step 17 | Go to Step 16 |
15 |
Important: The following Control Module replacement procedures must all be completed before attempting to operate the vehicle.
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. All of the above procedures are located in the gasoline service manual. 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 |
