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 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 with a scan tool. |
Diagnostic Aids
The most likely cause of this DTC is an improperly operating engine coolant system and thermostat. Go to Thermostat Diagnosis in the Engine Cooling section of the gasoline service manual 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 - 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.
-
Ensure that the engine can reach proper operating temperature in a timely manner before continuing with ECT sensor diagnosis.
-
This step determines if the Alternative Fuels ECM can monitor an open ECT signal circuit - high voltage.
-
This step determines if the Alternative Fuels ECM can monitor a shorted ECT signal circuit - low voltage.
-
This step determines if the ECT sensor is accurately monitoring engine coolant temperature.
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) |
Verify proper cooling system and thermostat operation. Refer to Thermostat Diagnosis in the Engine Cooling section of the G Van Service Manual. Was a cooling system repair made? | -- | Go to Step 11 | Go to Step 3 | |
Additional DTCs may set. Clear DTCs when diagnosis is complete. Does the ECT sensor data parameter indicate ECT voltage greater than the specified value? | 4.8 V | Go to Step 4 | Go to Step 7 | |
Connect a fused jumper between the ECT sensor connector signal and ground circuit terminals. Additional DTCs may set. Clear DTCs when diagnosis is complete. Does the ECT sensor data parameter indicate ECT voltage less than the specified value? | 0.019 V | Go to Step 5 | Go to Step 8 | |
Caution: To avoid being burned, do not remove the radiator cap or surge tank cap while the engine is hot. The cooling system will release scalding fluid and steam under pressure if radiator cap or surge tank cap is removed while the engine and radiator are still hot. Does the ECT sensor data parameter indicate a temperature near the actual engine coolant temperature? | -- | Go to Step 6 | Go to Step 9 | |
6 | The fault is not present. Refer to Diagnostic Aids. Are any DTCs stored that have not been diagnosed? | -- | Go to Intermittent Conditions | |
7 |
Was a wiring or terminal repair made? | -- | Go to Step 11 | Go to Step 10 |
8 |
Was a wiring or terminal repair made? | -- | Go to Step 11 | Go to Step 10 |
9 | 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 11 | -- |
10 |
Is the replacement complete? | -- | Go to Step 11 | -- |
11 |
Did this DTC run and pass? | -- | System OK | Go to Step 2 |
